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    Subject[14/63] mm: swap: unlock swapfile inode mutex before closing file on bad swapfiles
    2.6.38-stable review patch.  If anyone has any objections, please let us know.

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

    From: Mel Gorman <mgorman@suse.de>

    commit 52c50567d8ab0a0a87f12cceaa4194967854f0bd upstream.

    If an administrator tries to swapon a file backed by NFS, the inode mutex is
    taken (as it is for any swapfile) but later identified to be a bad swapfile
    due to the lack of bmap and tries to cleanup. During cleanup, an attempt is
    made to close the file but with inode->i_mutex still held. Closing an NFS
    file syncs it which tries to acquire the inode mutex leading to deadlock. If
    lockdep is enabled the following appears on the console;

    =============================================
    [ INFO: possible recursive locking detected ]
    2.6.38-rc8-autobuild #1
    ---------------------------------------------
    swapon/2192 is trying to acquire lock:
    (&sb->s_type->i_mutex_key#13){+.+.+.}, at: vfs_fsync_range+0x47/0x7c

    but task is already holding lock:
    (&sb->s_type->i_mutex_key#13){+.+.+.}, at: sys_swapon+0x28d/0xae7

    other info that might help us debug this:
    1 lock held by swapon/2192:
    #0: (&sb->s_type->i_mutex_key#13){+.+.+.}, at: sys_swapon+0x28d/0xae7

    stack backtrace:
    Pid: 2192, comm: swapon Not tainted 2.6.38-rc8-autobuild #1
    Call Trace:
    __lock_acquire+0x2eb/0x1623
    find_get_pages_tag+0x14a/0x174
    pagevec_lookup_tag+0x25/0x2e
    vfs_fsync_range+0x47/0x7c
    lock_acquire+0xd3/0x100
    vfs_fsync_range+0x47/0x7c
    nfs_flush_one+0x0/0xdf [nfs]
    mutex_lock_nested+0x40/0x2b1
    vfs_fsync_range+0x47/0x7c
    vfs_fsync_range+0x47/0x7c
    vfs_fsync+0x1c/0x1e
    nfs_file_flush+0x64/0x69 [nfs]
    filp_close+0x43/0x72
    sys_swapon+0xa39/0xae7
    sysret_check+0x2e/0x69
    system_call_fastpath+0x16/0x1b

    This patch releases the mutex if its held before calling filep_close()
    so swapon fails as expected without deadlock when the swapfile is backed
    by NFS. If accepted for 2.6.39, it should also be considered a -stable
    candidate for 2.6.38 and 2.6.37.

    Signed-off-by: Mel Gorman <mgorman@suse.de>
    Acked-by: Hugh Dickins <hughd@google.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    mm/swapfile.c | 7 ++++++-
    1 file changed, 6 insertions(+), 1 deletion(-)

    --- a/mm/swapfile.c
    +++ b/mm/swapfile.c
    @@ -2149,8 +2149,13 @@ bad_swap_2:
    p->flags = 0;
    spin_unlock(&swap_lock);
    vfree(swap_map);
    - if (swap_file)
    + if (swap_file) {
    + if (did_down) {
    + mutex_unlock(&inode->i_mutex);
    + did_down = 0;
    + }
    filp_close(swap_file, NULL);
    + }
    out:
    if (page && !IS_ERR(page)) {
    kunmap(page);



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