From 9590544694becc64f4874963dbfc4b4d391024b7 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Wed, 24 Sep 2014 11:28:32 +1000 Subject: NFS: avoid deadlocks with loop-back mounted NFS filesystems. Support for loop-back mounted NFS filesystems is useful when NFS is used to access shared storage in a high-availability cluster. If the node running the NFS server fails, some other node can mount the filesystem and start providing NFS service. If that node already had the filesystem NFS mounted, it will now have it loop-back mounted. nfsd can suffer a deadlock when allocating memory and entering direct reclaim. While direct reclaim does not write to the NFS filesystem it can send and wait for a COMMIT through nfs_release_page(). This patch modifies nfs_release_page() to wait a limited time for the commit to complete - one second. If the commit doesn't complete in this time, nfs_release_page() will fail. This means it might now fail in some cases where it wouldn't before. These cases are only when 'gfp' includes '__GFP_WAIT'. nfs_release_page() is only called by try_to_release_page(), and that can only be called on an NFS page with required 'gfp' flags from - page_cache_pipe_buf_steal() in splice.c - shrink_page_list() in vmscan.c - invalidate_inode_pages2_range() in truncate.c The first two handle failure quite safely. The last is only called after ->launder_page() has been called, and that will have waited for the commit to finish already. So aborting if the commit takes longer than 1 second is perfectly safe. Signed-off-by: NeilBrown Acked-by: Jeff Layton Signed-off-by: Trond Myklebust --- fs/nfs/write.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'fs/nfs/write.c') diff --git a/fs/nfs/write.c b/fs/nfs/write.c index a623b00530c3..c063a4e70354 100644 --- a/fs/nfs/write.c +++ b/fs/nfs/write.c @@ -705,6 +705,8 @@ static void nfs_inode_remove_request(struct nfs_page *req) if (likely(!PageSwapCache(head->wb_page))) { set_page_private(head->wb_page, 0); ClearPagePrivate(head->wb_page); + smp_mb__after_atomic(); + wake_up_page(head->wb_page, PG_private); clear_bit(PG_MAPPED, &head->wb_flags); } nfsi->npages--; -- cgit v1.2.3