From: NeilBrown Date: Thu, 13 Jun 2013 02:53:42 +0000 (+1000) Subject: sunrpc/cache: remove races with queuing an upcall. X-Git-Tag: v3.11-rc1~32^2~7 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f9e1aedc6c79f18bb56caa3735b94217c4ec1e0c;p=pandora-kernel.git sunrpc/cache: remove races with queuing an upcall. We currently queue an upcall after setting CACHE_PENDING, and dequeue after clearing CACHE_PENDING. So a request should only be present when CACHE_PENDING is set. However we don't combine the test and the enqueue/dequeue in a protected region, so it is possible (if unlikely) for a race to result in a request being queued without CACHE_PENDING set, or a request to be absent despite CACHE_PENDING. So: include a test for CACHE_PENDING inside the regions of enqueue and dequeue where queue_lock is held, and abort the operation if the value is not as expected. Also remove the early 'return' from cache_dequeue() to ensure that it always removes all entries: As there is no locking between setting CACHE_PENDING and calling sunrpc_cache_pipe_upcall it is not inconceivable for some other thread to clear CACHE_PENDING and then someone else to set it and call sunrpc_cache_pipe_upcall, both before the original threads completed the call. With this, it perfectly safe and correct to: - call cache_dequeue() if and only if we have just cleared CACHE_PENDING - call sunrpc_cache_pipe_upcall() (via cache_make_upcall) if and only if we have just set CACHE_PENDING. Reported-by: Bodo Stroesser Signed-off-by: NeilBrown Signed-off-by: Bodo Stroesser Signed-off-by: J. Bruce Fields --- Reading git-diff-tree failed