[PATCH AUTOSEL 5.0 005/317] gfs2: fix race between gfs2_freeze_func and unmount

Sasha Levin
2019-05-22T19:59:07Z

From: Abhi Das <adas@redhat.com>

[ Upstream commit 8f91821990fd6f170a5dca79697a441181a41b16 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/gfs2/incore.h | 1 +
fs/gfs2/super.c | 8 +++++---
2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index e10e0b0a7cd58..e1a33d2881213 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 ca71163ff7cfd..360206704a14c 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);
}

/**
--
2.20.1