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author | Christophe Saout <christophe@saout.de> | 2006-11-05 17:42:48 (GMT) |
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committer | Trond Myklebust <Trond.Myklebust@netapp.com> | 2006-12-06 15:46:24 (GMT) |
commit | cc4dc59e5580d6c0de1685a25b74d32175f43434 (patch) | |
tree | 61de2e40ba38b93027124d691308fc4405ef35d2 /fs/nfs | |
parent | ec0bf39a471bf6fcd01def2bd677128cea940b73 (diff) | |
download | linux-cc4dc59e5580d6c0de1685a25b74d32175f43434.tar.xz |
Subject: Re: [PATCH] Fix SUNRPC wakeup/execute race condition
The sunrpc scheduler contains a race condition that can let an RPC
task end up being neither running nor on any wait queue. The race takes
place between rpc_make_runnable (called from rpc_wake_up_task) and
__rpc_execute under the following condition:
First __rpc_execute calls tk_action which puts the task on some wait
queue. The task is dequeued by another process before __rpc_execute
continues its execution. While executing rpc_make_runnable exactly after
setting the task `running' bit and before clearing the `queued' bit
__rpc_execute picks up execution, clears `running' and subsequently
both functions fall through, both under the false assumption somebody
else took the job.
Swapping rpc_test_and_set_running with rpc_clear_queued in
rpc_make_runnable fixes that hole. This introduces another possible
race condition that can be handled by checking for `queued' after
setting the `running' bit.
Bug noticed on a 4-way x86_64 system under XEN with an NFSv4 server
on the same physical machine, apparently one of the few ways to hit
this race condition at all.
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Christophe Saout <christophe@saout.de>
Signed-off-by: Trond Myklebust <trond.myklebust@fys.uio.no>
Diffstat (limited to 'fs/nfs')
0 files changed, 0 insertions, 0 deletions