e3db7691e9
NFS: Fix race in nfs_release_page()
invalidate_inode_pages2() may find the dirty bit has been set on a page
owing to the fact that the page may still be mapped after it was locked.
Only after the call to unmap_mapping_range() are we sure that the page
can no longer be dirtied.
In order to fix this, NFS has hooked the releasepage() method and tries
to write the page out between the call to unmap_mapping_range() and the
call to remove_mapping(). This, however leads to deadlocks in the page
reclaim code, where the page may be locked without holding a reference
to the inode or dentry.
Fix is to add a new address_space_operation, launder_page(), which will
attempt to write out a dirty page without releasing the page lock.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Also, the bare SetPageDirty() can skew all sort of accounting leading to
other nasties.
[akpm@osdl.org: cleanup]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
528 lines
21 KiB
Plaintext
528 lines
21 KiB
Plaintext
The text below describes the locking rules for VFS-related methods.
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It is (believed to be) up-to-date. *Please*, if you change anything in
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prototypes or locking protocols - update this file. And update the relevant
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instances in the tree, don't leave that to maintainers of filesystems/devices/
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etc. At the very least, put the list of dubious cases in the end of this file.
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Don't turn it into log - maintainers of out-of-the-tree code are supposed to
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be able to use diff(1).
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Thing currently missing here: socket operations. Alexey?
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--------------------------- dentry_operations --------------------------
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prototypes:
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int (*d_revalidate)(struct dentry *, int);
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int (*d_hash) (struct dentry *, struct qstr *);
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int (*d_compare) (struct dentry *, struct qstr *, struct qstr *);
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int (*d_delete)(struct dentry *);
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void (*d_release)(struct dentry *);
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void (*d_iput)(struct dentry *, struct inode *);
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locking rules:
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none have BKL
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dcache_lock rename_lock ->d_lock may block
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d_revalidate: no no no yes
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d_hash no no no yes
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d_compare: no yes no no
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d_delete: yes no yes no
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d_release: no no no yes
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d_iput: no no no yes
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--------------------------- inode_operations ---------------------------
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prototypes:
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int (*create) (struct inode *,struct dentry *,int, struct nameidata *);
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struct dentry * (*lookup) (struct inode *,struct dentry *, struct nameid
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ata *);
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int (*link) (struct dentry *,struct inode *,struct dentry *);
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int (*unlink) (struct inode *,struct dentry *);
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int (*symlink) (struct inode *,struct dentry *,const char *);
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int (*mkdir) (struct inode *,struct dentry *,int);
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int (*rmdir) (struct inode *,struct dentry *);
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int (*mknod) (struct inode *,struct dentry *,int,dev_t);
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int (*rename) (struct inode *, struct dentry *,
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struct inode *, struct dentry *);
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int (*readlink) (struct dentry *, char __user *,int);
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int (*follow_link) (struct dentry *, struct nameidata *);
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void (*truncate) (struct inode *);
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int (*permission) (struct inode *, int, struct nameidata *);
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int (*setattr) (struct dentry *, struct iattr *);
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int (*getattr) (struct vfsmount *, struct dentry *, struct kstat *);
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int (*setxattr) (struct dentry *, const char *,const void *,size_t,int);
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ssize_t (*getxattr) (struct dentry *, const char *, void *, size_t);
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ssize_t (*listxattr) (struct dentry *, char *, size_t);
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int (*removexattr) (struct dentry *, const char *);
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locking rules:
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all may block, none have BKL
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i_sem(inode)
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lookup: yes
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create: yes
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link: yes (both)
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mknod: yes
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symlink: yes
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mkdir: yes
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unlink: yes (both)
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rmdir: yes (both) (see below)
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rename: yes (all) (see below)
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readlink: no
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follow_link: no
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truncate: yes (see below)
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setattr: yes
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permission: no
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getattr: no
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setxattr: yes
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getxattr: no
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listxattr: no
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removexattr: yes
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Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_sem on
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victim.
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cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem.
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->truncate() is never called directly - it's a callback, not a
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method. It's called by vmtruncate() - library function normally used by
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->setattr(). Locking information above applies to that call (i.e. is
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inherited from ->setattr() - vmtruncate() is used when ATTR_SIZE had been
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passed).
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See Documentation/filesystems/directory-locking for more detailed discussion
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of the locking scheme for directory operations.
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--------------------------- super_operations ---------------------------
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prototypes:
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struct inode *(*alloc_inode)(struct super_block *sb);
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void (*destroy_inode)(struct inode *);
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void (*read_inode) (struct inode *);
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void (*dirty_inode) (struct inode *);
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int (*write_inode) (struct inode *, int);
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void (*put_inode) (struct inode *);
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void (*drop_inode) (struct inode *);
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void (*delete_inode) (struct inode *);
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void (*put_super) (struct super_block *);
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void (*write_super) (struct super_block *);
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int (*sync_fs)(struct super_block *sb, int wait);
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void (*write_super_lockfs) (struct super_block *);
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void (*unlockfs) (struct super_block *);
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int (*statfs) (struct dentry *, struct kstatfs *);
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int (*remount_fs) (struct super_block *, int *, char *);
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void (*clear_inode) (struct inode *);
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void (*umount_begin) (struct super_block *);
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int (*show_options)(struct seq_file *, struct vfsmount *);
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ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
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ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
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locking rules:
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All may block.
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BKL s_lock s_umount
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alloc_inode: no no no
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destroy_inode: no
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read_inode: no (see below)
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dirty_inode: no (must not sleep)
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write_inode: no
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put_inode: no
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drop_inode: no !!!inode_lock!!!
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delete_inode: no
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put_super: yes yes no
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write_super: no yes read
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sync_fs: no no read
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write_super_lockfs: ?
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unlockfs: ?
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statfs: no no no
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remount_fs: yes yes maybe (see below)
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clear_inode: no
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umount_begin: yes no no
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show_options: no (vfsmount->sem)
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quota_read: no no no (see below)
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quota_write: no no no (see below)
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->read_inode() is not a method - it's a callback used in iget().
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->remount_fs() will have the s_umount lock if it's already mounted.
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When called from get_sb_single, it does NOT have the s_umount lock.
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->quota_read() and ->quota_write() functions are both guaranteed to
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be the only ones operating on the quota file by the quota code (via
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dqio_sem) (unless an admin really wants to screw up something and
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writes to quota files with quotas on). For other details about locking
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see also dquot_operations section.
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--------------------------- file_system_type ---------------------------
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prototypes:
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int (*get_sb) (struct file_system_type *, int,
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const char *, void *, struct vfsmount *);
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void (*kill_sb) (struct super_block *);
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locking rules:
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may block BKL
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get_sb yes yes
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kill_sb yes yes
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->get_sb() returns error or 0 with locked superblock attached to the vfsmount
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(exclusive on ->s_umount).
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->kill_sb() takes a write-locked superblock, does all shutdown work on it,
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unlocks and drops the reference.
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--------------------------- address_space_operations --------------------------
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prototypes:
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int (*writepage)(struct page *page, struct writeback_control *wbc);
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int (*readpage)(struct file *, struct page *);
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int (*sync_page)(struct page *);
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int (*writepages)(struct address_space *, struct writeback_control *);
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int (*set_page_dirty)(struct page *page);
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int (*readpages)(struct file *filp, struct address_space *mapping,
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struct list_head *pages, unsigned nr_pages);
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int (*prepare_write)(struct file *, struct page *, unsigned, unsigned);
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int (*commit_write)(struct file *, struct page *, unsigned, unsigned);
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sector_t (*bmap)(struct address_space *, sector_t);
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int (*invalidatepage) (struct page *, unsigned long);
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int (*releasepage) (struct page *, int);
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int (*direct_IO)(int, struct kiocb *, const struct iovec *iov,
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loff_t offset, unsigned long nr_segs);
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int (*launder_page) (struct page *);
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locking rules:
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All except set_page_dirty may block
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BKL PageLocked(page)
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writepage: no yes, unlocks (see below)
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readpage: no yes, unlocks
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sync_page: no maybe
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writepages: no
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set_page_dirty no no
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readpages: no
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prepare_write: no yes
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commit_write: no yes
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bmap: yes
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invalidatepage: no yes
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releasepage: no yes
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direct_IO: no
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launder_page: no yes
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->prepare_write(), ->commit_write(), ->sync_page() and ->readpage()
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may be called from the request handler (/dev/loop).
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->readpage() unlocks the page, either synchronously or via I/O
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completion.
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->readpages() populates the pagecache with the passed pages and starts
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I/O against them. They come unlocked upon I/O completion.
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->writepage() is used for two purposes: for "memory cleansing" and for
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"sync". These are quite different operations and the behaviour may differ
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depending upon the mode.
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If writepage is called for sync (wbc->sync_mode != WBC_SYNC_NONE) then
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it *must* start I/O against the page, even if that would involve
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blocking on in-progress I/O.
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If writepage is called for memory cleansing (sync_mode ==
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WBC_SYNC_NONE) then its role is to get as much writeout underway as
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possible. So writepage should try to avoid blocking against
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currently-in-progress I/O.
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If the filesystem is not called for "sync" and it determines that it
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would need to block against in-progress I/O to be able to start new I/O
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against the page the filesystem should redirty the page with
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redirty_page_for_writepage(), then unlock the page and return zero.
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This may also be done to avoid internal deadlocks, but rarely.
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If the filesytem is called for sync then it must wait on any
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in-progress I/O and then start new I/O.
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The filesystem should unlock the page synchronously, before returning to the
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caller, unless ->writepage() returns special WRITEPAGE_ACTIVATE
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value. WRITEPAGE_ACTIVATE means that page cannot really be written out
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currently, and VM should stop calling ->writepage() on this page for some
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time. VM does this by moving page to the head of the active list, hence the
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name.
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Unless the filesystem is going to redirty_page_for_writepage(), unlock the page
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and return zero, writepage *must* run set_page_writeback() against the page,
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followed by unlocking it. Once set_page_writeback() has been run against the
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page, write I/O can be submitted and the write I/O completion handler must run
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end_page_writeback() once the I/O is complete. If no I/O is submitted, the
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filesystem must run end_page_writeback() against the page before returning from
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writepage.
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That is: after 2.5.12, pages which are under writeout are *not* locked. Note,
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if the filesystem needs the page to be locked during writeout, that is ok, too,
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the page is allowed to be unlocked at any point in time between the calls to
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set_page_writeback() and end_page_writeback().
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Note, failure to run either redirty_page_for_writepage() or the combination of
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set_page_writeback()/end_page_writeback() on a page submitted to writepage
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will leave the page itself marked clean but it will be tagged as dirty in the
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radix tree. This incoherency can lead to all sorts of hard-to-debug problems
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in the filesystem like having dirty inodes at umount and losing written data.
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->sync_page() locking rules are not well-defined - usually it is called
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with lock on page, but that is not guaranteed. Considering the currently
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existing instances of this method ->sync_page() itself doesn't look
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well-defined...
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->writepages() is used for periodic writeback and for syscall-initiated
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sync operations. The address_space should start I/O against at least
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*nr_to_write pages. *nr_to_write must be decremented for each page which is
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written. The address_space implementation may write more (or less) pages
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than *nr_to_write asks for, but it should try to be reasonably close. If
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nr_to_write is NULL, all dirty pages must be written.
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writepages should _only_ write pages which are present on
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mapping->io_pages.
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->set_page_dirty() is called from various places in the kernel
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when the target page is marked as needing writeback. It may be called
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under spinlock (it cannot block) and is sometimes called with the page
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not locked.
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->bmap() is currently used by legacy ioctl() (FIBMAP) provided by some
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filesystems and by the swapper. The latter will eventually go away. All
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instances do not actually need the BKL. Please, keep it that way and don't
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breed new callers.
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->invalidatepage() is called when the filesystem must attempt to drop
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some or all of the buffers from the page when it is being truncated. It
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returns zero on success. If ->invalidatepage is zero, the kernel uses
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block_invalidatepage() instead.
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->releasepage() is called when the kernel is about to try to drop the
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buffers from the page in preparation for freeing it. It returns zero to
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indicate that the buffers are (or may be) freeable. If ->releasepage is zero,
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the kernel assumes that the fs has no private interest in the buffers.
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->launder_page() may be called prior to releasing a page if
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it is still found to be dirty. It returns zero if the page was successfully
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cleaned, or an error value if not. Note that in order to prevent the page
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getting mapped back in and redirtied, it needs to be kept locked
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across the entire operation.
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Note: currently almost all instances of address_space methods are
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using BKL for internal serialization and that's one of the worst sources
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of contention. Normally they are calling library functions (in fs/buffer.c)
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and pass foo_get_block() as a callback (on local block-based filesystems,
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indeed). BKL is not needed for library stuff and is usually taken by
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foo_get_block(). It's an overkill, since block bitmaps can be protected by
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internal fs locking and real critical areas are much smaller than the areas
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filesystems protect now.
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----------------------- file_lock_operations ------------------------------
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prototypes:
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void (*fl_insert)(struct file_lock *); /* lock insertion callback */
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void (*fl_remove)(struct file_lock *); /* lock removal callback */
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void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
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void (*fl_release_private)(struct file_lock *);
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locking rules:
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BKL may block
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fl_insert: yes no
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fl_remove: yes no
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fl_copy_lock: yes no
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fl_release_private: yes yes
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----------------------- lock_manager_operations ---------------------------
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prototypes:
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int (*fl_compare_owner)(struct file_lock *, struct file_lock *);
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void (*fl_notify)(struct file_lock *); /* unblock callback */
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void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
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void (*fl_release_private)(struct file_lock *);
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void (*fl_break)(struct file_lock *); /* break_lease callback */
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locking rules:
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BKL may block
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fl_compare_owner: yes no
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fl_notify: yes no
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fl_copy_lock: yes no
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fl_release_private: yes yes
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fl_break: yes no
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Currently only NFSD and NLM provide instances of this class. None of the
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them block. If you have out-of-tree instances - please, show up. Locking
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in that area will change.
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--------------------------- buffer_head -----------------------------------
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prototypes:
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void (*b_end_io)(struct buffer_head *bh, int uptodate);
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locking rules:
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called from interrupts. In other words, extreme care is needed here.
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bh is locked, but that's all warranties we have here. Currently only RAID1,
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highmem, fs/buffer.c, and fs/ntfs/aops.c are providing these. Block devices
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call this method upon the IO completion.
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--------------------------- block_device_operations -----------------------
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prototypes:
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int (*open) (struct inode *, struct file *);
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int (*release) (struct inode *, struct file *);
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int (*ioctl) (struct inode *, struct file *, unsigned, unsigned long);
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int (*media_changed) (struct gendisk *);
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int (*revalidate_disk) (struct gendisk *);
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locking rules:
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BKL bd_sem
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open: yes yes
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release: yes yes
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ioctl: yes no
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media_changed: no no
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revalidate_disk: no no
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The last two are called only from check_disk_change().
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--------------------------- file_operations -------------------------------
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prototypes:
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loff_t (*llseek) (struct file *, loff_t, int);
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ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
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ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
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ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
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ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
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int (*readdir) (struct file *, void *, filldir_t);
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unsigned int (*poll) (struct file *, struct poll_table_struct *);
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int (*ioctl) (struct inode *, struct file *, unsigned int,
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unsigned long);
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long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
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long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
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int (*mmap) (struct file *, struct vm_area_struct *);
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int (*open) (struct inode *, struct file *);
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int (*flush) (struct file *);
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int (*release) (struct inode *, struct file *);
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int (*fsync) (struct file *, struct dentry *, int datasync);
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int (*aio_fsync) (struct kiocb *, int datasync);
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int (*fasync) (int, struct file *, int);
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int (*lock) (struct file *, int, struct file_lock *);
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ssize_t (*readv) (struct file *, const struct iovec *, unsigned long,
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loff_t *);
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ssize_t (*writev) (struct file *, const struct iovec *, unsigned long,
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loff_t *);
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ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t,
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void __user *);
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ssize_t (*sendpage) (struct file *, struct page *, int, size_t,
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loff_t *, int);
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unsigned long (*get_unmapped_area)(struct file *, unsigned long,
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unsigned long, unsigned long, unsigned long);
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int (*check_flags)(int);
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int (*dir_notify)(struct file *, unsigned long);
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};
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locking rules:
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All except ->poll() may block.
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BKL
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llseek: no (see below)
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read: no
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aio_read: no
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write: no
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aio_write: no
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readdir: no
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poll: no
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ioctl: yes (see below)
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unlocked_ioctl: no (see below)
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compat_ioctl: no
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mmap: no
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open: maybe (see below)
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flush: no
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release: no
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fsync: no (see below)
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aio_fsync: no
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fasync: yes (see below)
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lock: yes
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readv: no
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writev: no
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sendfile: no
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sendpage: no
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get_unmapped_area: no
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check_flags: no
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dir_notify: no
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->llseek() locking has moved from llseek to the individual llseek
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implementations. If your fs is not using generic_file_llseek, you
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need to acquire and release the appropriate locks in your ->llseek().
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For many filesystems, it is probably safe to acquire the inode
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semaphore. Note some filesystems (i.e. remote ones) provide no
|
|
protection for i_size so you will need to use the BKL.
|
|
|
|
->open() locking is in-transit: big lock partially moved into the methods.
|
|
The only exception is ->open() in the instances of file_operations that never
|
|
end up in ->i_fop/->proc_fops, i.e. ones that belong to character devices
|
|
(chrdev_open() takes lock before replacing ->f_op and calling the secondary
|
|
method. As soon as we fix the handling of module reference counters all
|
|
instances of ->open() will be called without the BKL.
|
|
|
|
Note: ext2_release() was *the* source of contention on fs-intensive
|
|
loads and dropping BKL on ->release() helps to get rid of that (we still
|
|
grab BKL for cases when we close a file that had been opened r/w, but that
|
|
can and should be done using the internal locking with smaller critical areas).
|
|
Current worst offender is ext2_get_block()...
|
|
|
|
->fasync() is a mess. This area needs a big cleanup and that will probably
|
|
affect locking.
|
|
|
|
->readdir() and ->ioctl() on directories must be changed. Ideally we would
|
|
move ->readdir() to inode_operations and use a separate method for directory
|
|
->ioctl() or kill the latter completely. One of the problems is that for
|
|
anything that resembles union-mount we won't have a struct file for all
|
|
components. And there are other reasons why the current interface is a mess...
|
|
|
|
->ioctl() on regular files is superceded by the ->unlocked_ioctl() that
|
|
doesn't take the BKL.
|
|
|
|
->read on directories probably must go away - we should just enforce -EISDIR
|
|
in sys_read() and friends.
|
|
|
|
->fsync() has i_sem on inode.
|
|
|
|
--------------------------- dquot_operations -------------------------------
|
|
prototypes:
|
|
int (*initialize) (struct inode *, int);
|
|
int (*drop) (struct inode *);
|
|
int (*alloc_space) (struct inode *, qsize_t, int);
|
|
int (*alloc_inode) (const struct inode *, unsigned long);
|
|
int (*free_space) (struct inode *, qsize_t);
|
|
int (*free_inode) (const struct inode *, unsigned long);
|
|
int (*transfer) (struct inode *, struct iattr *);
|
|
int (*write_dquot) (struct dquot *);
|
|
int (*acquire_dquot) (struct dquot *);
|
|
int (*release_dquot) (struct dquot *);
|
|
int (*mark_dirty) (struct dquot *);
|
|
int (*write_info) (struct super_block *, int);
|
|
|
|
These operations are intended to be more or less wrapping functions that ensure
|
|
a proper locking wrt the filesystem and call the generic quota operations.
|
|
|
|
What filesystem should expect from the generic quota functions:
|
|
|
|
FS recursion Held locks when called
|
|
initialize: yes maybe dqonoff_sem
|
|
drop: yes -
|
|
alloc_space: ->mark_dirty() -
|
|
alloc_inode: ->mark_dirty() -
|
|
free_space: ->mark_dirty() -
|
|
free_inode: ->mark_dirty() -
|
|
transfer: yes -
|
|
write_dquot: yes dqonoff_sem or dqptr_sem
|
|
acquire_dquot: yes dqonoff_sem or dqptr_sem
|
|
release_dquot: yes dqonoff_sem or dqptr_sem
|
|
mark_dirty: no -
|
|
write_info: yes dqonoff_sem
|
|
|
|
FS recursion means calling ->quota_read() and ->quota_write() from superblock
|
|
operations.
|
|
|
|
->alloc_space(), ->alloc_inode(), ->free_space(), ->free_inode() are called
|
|
only directly by the filesystem and do not call any fs functions only
|
|
the ->mark_dirty() operation.
|
|
|
|
More details about quota locking can be found in fs/dquot.c.
|
|
|
|
--------------------------- vm_operations_struct -----------------------------
|
|
prototypes:
|
|
void (*open)(struct vm_area_struct*);
|
|
void (*close)(struct vm_area_struct*);
|
|
struct page *(*nopage)(struct vm_area_struct*, unsigned long, int *);
|
|
|
|
locking rules:
|
|
BKL mmap_sem
|
|
open: no yes
|
|
close: no yes
|
|
nopage: no yes
|
|
|
|
================================================================================
|
|
Dubious stuff
|
|
|
|
(if you break something or notice that it is broken and do not fix it yourself
|
|
- at least put it here)
|
|
|
|
ipc/shm.c::shm_delete() - may need BKL.
|
|
->read() and ->write() in many drivers are (probably) missing BKL.
|
|
drivers/sgi/char/graphics.c::sgi_graphics_nopage() - may need BKL.
|