The RDMACTXT_F_LAST_CTXT bit was getting set incorrectly
when the last chunk in the read-list spanned multiple pages. This
resulted in a kernel panic when the wrong context was used to
build the RPC iovec page list.
RDMA_READ is used to fetch RPC data from the client for
NFS_WRITE requests. A scatter-gather is used to map the
advertised client side buffer to the server-side iovec and
associated page list.
WR contexts are used to convey which scatter-gather entries are
handled by each WR. When the write data is large, a single RPC may
require multiple RDMA_READ requests so the contexts for a single RPC
are chained together in a linked list. The last context in this list
is marked with a bit RDMACTXT_F_LAST_CTXT so that when this WR completes,
the CQ handler code can enqueue the RPC for processing.
The code in rdma_read_xdr was setting this bit on the last two
contexts on this list when the last read-list chunk spanned multiple
pages. This caused the svc_rdma_recvfrom logic to incorrectly build
the RPC and caused the kernel to crash because the second-to-last
context doesn't contain the iovec page list.
Modified the condition that sets this bit so that it correctly detects
the last context for the RPC.
Signed-off-by: Tom Tucker <tom@opengridcomputing.com>
Tested-by: Roland Dreier <rolandd@cisco.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The iWARP protocol limits RDMA read requests to a single scatter
entry. NFS/RDMA has code in rdma_read_max_sge() that is supposed to
limit the sge_count for RDMA read requests to 1, but the code to do
that is inside an #ifdef RDMA_TRANSPORT_IWARP block. In the mainline
kernel at least, RDMA_TRANSPORT_IWARP is an enum and not a
preprocessor #define, so the #ifdef'ed code is never compiled.
In my test of a kernel build with -j8 on an NFS/RDMA mount, this
problem eventually leads to trouble starting with:
svcrdma: Error posting send = -22
svcrdma : RDMA_READ error = -22
and things go downhill from there.
The trivial fix is to delete the #ifdef guard. The check seems to be
a remnant of when the NFS/RDMA code was not merged and needed to
compile against multiple kernel versions, although I don't think it
ever worked as intended. In any case now that the code is upstream
there's no need to test whether the RDMA_TRANSPORT_IWARP constant is
defined or not.
Without this patch, my kernel build on an NFS/RDMA mount using NetEffect
adapters quickly and 100% reproducibly failed with an error like:
ld: final link failed: Software caused connection abort
With the patch applied I was able to complete a kernel build on the
same setup.
(Tom Tucker says this is "actually an _ancient_ remnant when it had to
compile against iWARP vs. non-iWARP enabled OFA trees.")
Signed-off-by: Roland Dreier <rolandd@cisco.com>
Acked-by: Tom Tucker <tom@opengridcomputing.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This file implements the RDMA transport recvfrom function. The function
dequeues work reqeust completion contexts from an I/O list that it shares
with the I/O tasklet in svc_rdma_transport.c. For ONCRPC RDMA, an RPC may
not be complete when it is received. Instead, the RDMA header that precedes
the RPC message informs the transport where to get the RPC data from on
the client and where to place it in the RPC message before it is delivered
to the server. The svc_rdma_recvfrom function therefore, parses this RDMA
header and issues any necessary RDMA operations to fetch the remainder of
the RPC from the client.
Special handling is required when the request involves an RDMA_READ.
In this case, recvfrom submits the RDMA_READ requests to the underlying
transport driver and then returns 0. When the transport
completes the last RDMA_READ for the request, it enqueues it on a
read completion queue and enqueues the transport. The recvfrom code
favors this queue over the regular DTO queue when satisfying reads.
Signed-off-by: Tom Tucker <tom@opengridcomputing.com>
Acked-by: Neil Brown <neilb@suse.de>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
