linux-ext4 - [PATCH 6/6] jbd2: make the whole kjournald2 kthread NOFS safe

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Message-Id: <20170206140718.16222-7-mhocko@kernel.org>
Date:   Mon,  6 Feb 2017 15:07:18 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        <linux-fsdevel@...r.kernel.org>
Cc:     <linux-mm@...ck.org>, Dave Chinner <david@...morbit.com>,
        djwong@...nel.org, "Theodore Ts'o" <tytso@....edu>,
        Chris Mason <clm@...com>, David Sterba <dsterba@...e.cz>,
        Jan Kara <jack@...e.cz>, ceph-devel@...r.kernel.org,
        cluster-devel@...hat.com, linux-nfs@...r.kernel.org,
        logfs@...fs.org, linux-xfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-mtd@...ts.infradead.org, reiserfs-devel@...r.kernel.org,
        linux-ntfs-dev@...ts.sourceforge.net,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-afs@...ts.infradead.org, LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>
Subject: [PATCH 6/6] jbd2: make the whole kjournald2 kthread NOFS safe

From: Michal Hocko <mhocko@...e.com>

kjournald2 is central to the transaction commit processing. As such any
potential allocation from this kernel thread has to be GFP_NOFS. Make
sure to mark the whole kernel thread GFP_NOFS by the memalloc_nofs_save.

Suggested-by: Jan Kara <jack@...e.cz>
Reviewed-by: Jan Kara <jack@...e.cz>
Signed-off-by: Michal Hocko <mhocko@...e.com>
---
 fs/jbd2/journal.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 704139625fbe..662531a70ce1 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -206,6 +206,13 @@ static int kjournald2(void *arg)
 	wake_up(&journal->j_wait_done_commit);
 
 	/*
+	 * Make sure that no allocations from this kernel thread will ever recurse
+	 * to the fs layer because we are responsible for the transaction commit
+	 * and any fs involvement might get stuck waiting for the trasn. commit.
+	 */
+	memalloc_nofs_save();
+
+	/*
 	 * And now, wait forever for commit wakeup events.
 	 */
 	write_lock(&journal->j_state_lock);
-- 
2.11.0