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    Subject[PATCH 4.4 059/108] nfs/pnfs: fix nfs_direct_req ref leak when i/o falls back to the mds
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Scott Mayhew <smayhew@redhat.com>

    commit ba4a76f703ab7eb72941fdaac848502073d6e9ee upstream.

    Currently when falling back to doing I/O through the MDS (via
    pnfs_{read|write}_through_mds), the client frees the nfs_pgio_header
    without releasing the reference taken on the dreq
    via pnfs_generic_pg_{read|write}pages -> nfs_pgheader_init ->
    nfs_direct_pgio_init. It then takes another reference on the dreq via
    nfs_generic_pg_pgios -> nfs_pgheader_init -> nfs_direct_pgio_init and
    as a result the requester will become stuck in inode_dio_wait. Once
    that happens, other processes accessing the inode will become stuck as
    well.

    Ensure that pnfs_read_through_mds() and pnfs_write_through_mds() clean
    up correctly by calling hdr->completion_ops->completion() instead of
    calling hdr->release() directly.

    This can be reproduced (sometimes) by performing "storage failover
    takeover" commands on NetApp filer while doing direct I/O from a client.

    This can also be reproduced using SystemTap to simulate a failure while
    doing direct I/O from a client (from Dave Wysochanski
    <dwysocha@redhat.com>):

    stap -v -g -e 'probe module("nfs_layout_nfsv41_files").function("nfs4_fl_prepare_ds").return { $return=NULL; exit(); }'

    Suggested-by: Trond Myklebust <trond.myklebust@primarydata.com>
    Signed-off-by: Scott Mayhew <smayhew@redhat.com>
    Fixes: 1ca018d28d ("pNFS: Fix a memory leak when attempted pnfs fails")
    Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/nfs/pnfs.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/fs/nfs/pnfs.c
    +++ b/fs/nfs/pnfs.c
    @@ -1943,7 +1943,7 @@ pnfs_write_through_mds(struct nfs_pageio
    nfs_pageio_reset_write_mds(desc);
    mirror->pg_recoalesce = 1;
    }
    - hdr->release(hdr);
    + hdr->completion_ops->completion(hdr);
    }

    static enum pnfs_try_status
    @@ -2058,7 +2058,7 @@ pnfs_read_through_mds(struct nfs_pageio_
    nfs_pageio_reset_read_mds(desc);
    mirror->pg_recoalesce = 1;
    }
    - hdr->release(hdr);
    + hdr->completion_ops->completion(hdr);
    }

    /*

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