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ANDROID: scs: fix recursive spinlock in scs_check_usage

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Use cmpxchg instead of a spinlock in scs_check_usage() to avoid
deadlocks.

Bug: 157781894
Change-Id: I1701ccaf25fdbd34ce4798c6f93e220b1565fb34
(cherry picked from commit e929fb3f34326c669bff7863da32c90730fa7d72)
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
This commit is contained in:
Sami Tolvanen 2020-06-01 12:20:04 -07:00 committed by Will Deacon
parent f829d7f05b
commit e467b8c7db
1 changed files with 18 additions and 23 deletions
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41
kernel/scs.c
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@ -185,36 +185,31 @@ int scs_prepare(struct task_struct *tsk, int node)
}
#ifdef CONFIG_DEBUG_STACK_USAGE
static inline unsigned long scs_used(struct task_struct *tsk)
{
unsigned long *p = __scs_base(tsk);
unsigned long *end = scs_magic(p);
unsigned long s = (unsigned long)p;
while (p < end && READ_ONCE_NOCHECK(*p))
p++;
return (unsigned long)p - s;
}
static void scs_check_usage(struct task_struct *tsk)
{
static DEFINE_SPINLOCK(lock);
static unsigned long highest;
unsigned long used = scs_used(tsk);
if (used <= highest)
return;
unsigned long *p = __scs_base(tsk);
unsigned long *end = scs_magic(p);
unsigned long prev, curr = highest, used = 0;
spin_lock(&lock);
if (used > highest) {
pr_info("%s (%d): highest shadow stack usage: %lu bytes\n",
tsk->comm, task_pid_nr(tsk), used);
highest = used;
for (; p < end; ++p) {
if (!READ_ONCE_NOCHECK(*p))
break;
used += sizeof(*p);
}
spin_unlock(&lock);
while (used > curr) {
prev = cmpxchg_relaxed(&highest, curr, used);
if (prev == curr) {
pr_info("%s (%d): highest shadow stack usage: %lu bytes\n",
tsk->comm, task_pid_nr(tsk), used);
break;
}
curr = prev;
}
}
#else
static inline void scs_check_usage(struct task_struct *tsk)