gfs2: fix race between gfs2_freeze_func and unmount

As part of the freeze operation, gfs2_freeze_func() is left blocking
on a request to hold the sd_freeze_gl in SH. This glock is held in EX
by the gfs2_freeze() code.

A subsequent call to gfs2_unfreeze() releases the EXclusively held
sd_freeze_gl, which allows gfs2_freeze_func() to acquire it in SH and
resume its operation.

gfs2_unfreeze(), however, doesn't wait for gfs2_freeze_func() to complete.
If a umount is issued right after unfreeze, it could result in an
inconsistent filesystem because some journal data (statfs update) isn't
written out.

Refer to commit 24972557b12c for a more detailed explanation of how
freeze/unfreeze work.

This patch causes gfs2_unfreeze() to wait for gfs2_freeze_func() to
complete before returning to the user.

Signed-off-by: Abhi Das <adas@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

2 files changed, 6 insertions, 3 deletions

diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 78c8e761b321..b15755068593 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -621,6 +621,7 @@ enum {
         SDF_SKIP_DLM_UNLOCK     = 8,
         SDF_FORCE_AIL_FLUSH     = 9,
         SDF_AIL1_IO_ERROR       = 10,
+        SDF_FS_FROZEN           = 11,
 };
 
 enum gfs2_freeze_state {
diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index 6d89d0ecec2a..5b148cf03293 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -973,8 +973,7 @@ void gfs2_freeze_func(struct work_struct *work)
         if (error) {
                 printk(KERN_INFO "GFS2: couldn't get freeze lock : %d\n", error);
                 gfs2_assert_withdraw(sdp, 0);
-        }
-        else {
+        } else {
                 atomic_set(&sdp->sd_freeze_state, SFS_UNFROZEN);
                 error = thaw_super(sb);
                 if (error) {
@@ -987,6 +986,8 @@ void gfs2_freeze_func(struct work_struct *work)
                 gfs2_glock_dq_uninit(&freeze_gh);
         }
         deactivate_super(sb);
+        clear_bit_unlock(SDF_FS_FROZEN, &sdp->sd_flags);
+        wake_up_bit(&sdp->sd_flags, SDF_FS_FROZEN);
         return;
 }
 
@@ -1029,6 +1030,7 @@ static int gfs2_freeze(struct super_block *sb)
                 msleep(1000);
         }
         error = 0;
+        set_bit(SDF_FS_FROZEN, &sdp->sd_flags);
 out:
         mutex_unlock(&sdp->sd_freeze_mutex);
         return error;
@@ -1053,7 +1055,7 @@ static int gfs2_unfreeze(struct super_block *sb)
 
         gfs2_glock_dq_uninit(&sdp->sd_freeze_gh);
         mutex_unlock(&sdp->sd_freeze_mutex);
-        return 0;
+        return wait_on_bit(&sdp->sd_flags, SDF_FS_FROZEN, TASK_INTERRUPTIBLE);
 }
 
 /**