From d2224e7afbf2a6556f4f8f25bc0e96d99ec4d2bd Mon Sep 17 00:00:00 2001 From: Jeff Layton Date: Sun, 6 Mar 2011 17:14:13 +0000 Subject: [PATCH] nfs: close NFSv4 COMMIT vs. CLOSE race I've been adding in more artificial delays in the NFSv4 commit and close codepaths to uncover races. The kernel I'm testing has the patch to close the race in __rpc_wait_for_completion_task that's in Trond's cthon2011 branch. The reproducer I've been using does this in a loop: mkdir("DIR"); fd = open("DIR/FILE", O_WRONLY|O_CREAT|O_EXCL, 0644); write(fd, "abcdefg", 7); close(fd); unlink("DIR/FILE"); rmdir("DIR"); The above reproducer shouldn't result in any silly-renaming. However, when I add a "msleep(100)" just after the nfs_commit_clear_lock call in nfs_commit_release, I can almost always force one to occur. If I can force it to occur with that, then it can happen without that delay given the right timing. nfs_commit_inode waits for the NFS_INO_COMMIT bit to clear when called with FLUSH_SYNC set. nfs_commit_rpcsetup on the other hand does not wait for the task to complete before putting its reference to it, so the last reference get put in rpc_release task and gets queued to a workqueue. In this situation, the last open context reference may be put by the COMMIT release instead of the close() syscall. The close() syscall returns too quickly and the unlink runs while the d_count is still high since the COMMIT release hasn't put its dentry reference yet. Fix this by having rpc_commit_rpcsetup wait for the RPC call to complete before putting the task reference when FLUSH_SYNC is set. With this, the last reference is put by the process that's initiating the FLUSH_SYNC commit and the race is closed. Signed-off-by: Jeff Layton Signed-off-by: Trond Myklebust --- fs/nfs/write.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/nfs/write.c b/fs/nfs/write.c index c8278f4046cb..42b92d7a9cc4 100644 --- a/fs/nfs/write.c +++ b/fs/nfs/write.c @@ -1292,6 +1292,8 @@ static int nfs_commit_rpcsetup(struct list_head *head, task = rpc_run_task(&task_setup_data); if (IS_ERR(task)) return PTR_ERR(task); + if (how & FLUSH_SYNC) + rpc_wait_for_completion_task(task); rpc_put_task(task); return 0; } -- 2.30.2