• NeilBrown's avatar
    NFS: avoid deadlocks with loop-back mounted NFS filesystems. · 95905446
    NeilBrown authored
    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: default avatarNeilBrown <neilb@suse.de>
    Acked-by: default avatarJeff Layton <jlayton@primarydata.com>
    Signed-off-by: default avatarTrond Myklebust <trond.myklebust@primarydata.com>
    95905446
write.c 50.8 KB