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    Subject[PATCH 5.4 051/232] gfs2: Dont demote a glock until its revokes are written
    Date
    From: Bob Peterson <rpeterso@redhat.com>

    [ Upstream commit df5db5f9ee112e76b5202fbc331f990a0fc316d6 ]

    Before this patch, run_queue would demote glocks based on whether
    there are any more holders. But if the glock has pending revokes that
    haven't been written to the media, giving up the glock might end in
    file system corruption if the revokes never get written due to
    io errors, node crashes and fences, etc. In that case, another node
    will replay the metadata blocks associated with the glock, but
    because the revoke was never written, it could replay that block
    even though the glock had since been granted to another node who
    might have made changes.

    This patch changes the logic in run_queue so that it never demotes
    a glock until its count of pending revokes reaches zero.

    Signed-off-by: Bob Peterson <rpeterso@redhat.com>
    Reviewed-by: Andreas Gruenbacher <agruenba@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/gfs2/glock.c | 3 +++
    1 file changed, 3 insertions(+)

    diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
    index 0290a22ebccf5..21820a5b388fd 100644
    --- a/fs/gfs2/glock.c
    +++ b/fs/gfs2/glock.c
    @@ -639,6 +639,9 @@ __acquires(&gl->gl_lockref.lock)
    goto out_unlock;
    if (nonblock)
    goto out_sched;
    + smp_mb();
    + if (atomic_read(&gl->gl_revokes) != 0)
    + goto out_sched;
    set_bit(GLF_DEMOTE_IN_PROGRESS, &gl->gl_flags);
    GLOCK_BUG_ON(gl, gl->gl_demote_state == LM_ST_EXCLUSIVE);
    gl->gl_target = gl->gl_demote_state;
    --
    2.20.1


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