[XFS] fix NULL pointer dereference in xfs_log_force_umount

xfs_log_force_umount may be called very early during log recovery where

If we fail a buffer read in xlog_recover_do_inode_trans we abort the mount.
But at that point log recovery has started delayed writeback of inode
buffers.   As part of the aborted mount we try to flush out all delwri
buffers, but at that point we have already freed the superblock, and set
mp->m_sb_bp to NULL, and xfs_log_force_umount which gets called after
the inode buffer writeback trips over it.

Make xfs_log_force_umount a little more careful when accessing mp->m_sb_bp
to avoid this.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Eric Sandeen <sandeen@sandeen.net>
Signed-off-by: Niv Sardi <xaiki@sgi.com>

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 4bf44aef644c5d1cfdf84faa68e0d5e673de7707..8a5b05536a28c6118367e2fb1d7284836b198308 100644 (file)
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -3569,7 +3569,8 @@ xfs_log_force_umount(
        if (!log ||
            log->l_flags & XLOG_ACTIVE_RECOVERY) {
                mp->m_flags |= XFS_MOUNT_FS_SHUTDOWN;
-               XFS_BUF_DONE(mp->m_sb_bp);
+               if (mp->m_sb_bp)
+                       XFS_BUF_DONE(mp->m_sb_bp);
                return 0;
        }
 
@@ -3590,7 +3591,9 @@ xfs_log_force_umount(
        spin_lock(&log->l_icloglock);
        spin_lock(&log->l_grant_lock);
        mp->m_flags |= XFS_MOUNT_FS_SHUTDOWN;
-       XFS_BUF_DONE(mp->m_sb_bp);
+       if (mp->m_sb_bp)
+               XFS_BUF_DONE(mp->m_sb_bp);
+
        /*
         * This flag is sort of redundant because of the mount flag, but
         * it's good to maintain the separation between the log and the rest