linux-kernel - [PATCH 5.1 049/405] gfs2: fix race between gfs2_freeze

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Message-Id: <20190530030543.313272702@linuxfoundation.org>
Date:   Wed, 29 May 2019 20:00:47 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Abhi Das <adas@...hat.com>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.1 049/405] gfs2: fix race between gfs2_freeze_func and unmount

[ 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@...hat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.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 cdf07b408f54c..539e8dc5a3f6c 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