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    Subject[PATCH AUTOSEL 5.4 100/330] nfsd: Fix a soft lockup race in nfsd_file_mark_find_or_create()
    Date
    From: Trond Myklebust <trondmy@gmail.com>

    [ Upstream commit 90d2f1da832fd23290ef0c0d964d97501e5e8553 ]

    If nfsd_file_mark_find_or_create() keeps winning the race for the
    nfsd_file_fsnotify_group->mark_mutex against nfsd_file_mark_put()
    then it can soft lock up, since fsnotify_add_inode_mark() ends
    up always finding an existing entry.

    Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
    Signed-off-by: J. Bruce Fields <bfields@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/nfsd/filecache.c | 8 ++++++--
    1 file changed, 6 insertions(+), 2 deletions(-)

    diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
    index 3007b8945d388..51c08ae79063c 100644
    --- a/fs/nfsd/filecache.c
    +++ b/fs/nfsd/filecache.c
    @@ -133,9 +133,13 @@ nfsd_file_mark_find_or_create(struct nfsd_file *nf)
    struct nfsd_file_mark,
    nfm_mark));
    mutex_unlock(&nfsd_file_fsnotify_group->mark_mutex);
    - fsnotify_put_mark(mark);
    - if (likely(nfm))
    + if (nfm) {
    + fsnotify_put_mark(mark);
    break;
    + }
    + /* Avoid soft lockup race with nfsd_file_mark_put() */
    + fsnotify_destroy_mark(mark, nfsd_file_fsnotify_group);
    + fsnotify_put_mark(mark);
    } else
    mutex_unlock(&nfsd_file_fsnotify_group->mark_mutex);

    --
    2.25.1
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