[PATCH 5.18 0822/1095] jbd2: fix outstanding credits assert in jbd2_journal_commit_transaction()

Greg Kroah-Hartman
2022-08-15T22:30:00Z

From: Zhang Yi <yi.zhang@huawei.com>

[ Upstream commit a89573ce4ad32f19f43ec669771726817e185be0 ]

We catch an assert problem in jbd2_journal_commit_transaction() when
doing fsstress and request falut injection tests. The problem is
happened in a race condition between jbd2_journal_commit_transaction()
and ext4_end_io_end(). Firstly, ext4_writepages() writeback dirty pages
and start reserved handle, and then the journal was aborted due to some
previous metadata IO error, jbd2_journal_abort() start to commit current
running transaction, the committing procedure could be raced by
ext4_end_io_end() and lead to subtract j_reserved_credits twice from
commit_transaction->t_outstanding_credits, finally the
t_outstanding_credits is mistakenly smaller than t_nr_buffers and
trigger assert.

kjournald2 kworker

jbd2_journal_commit_transaction()
write_unlock(&journal->j_state_lock);
atomic_sub(j_reserved_credits, t_outstanding_credits); //sub once

jbd2_journal_start_reserved()
start_this_handle() //detect aborted journal
jbd2_journal_free_reserved() //get running transaction
read_lock(&journal->j_state_lock)
__jbd2_journal_unreserve_handle()
atomic_sub(j_reserved_credits, t_outstanding_credits);
//sub again
read_unlock(&journal->j_state_lock);

journal->j_running_transaction = NULL;
J_ASSERT(t_nr_buffers <= t_outstanding_credits) //bomb!!!

Fix this issue by using journal->j_state_lock to protect the subtraction
in jbd2_journal_commit_transaction().

Fixes: 96f1e0974575 ("jbd2: avoid long hold times of j_state_lock while committing a transaction")
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220611130426.2013258-1-yi.zhang@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/jbd2/commit.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index ac7f067b7bdd..f306b52b8e0b 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -551,13 +551,13 @@ void jbd2_journal_commit_transaction(journal_t *journal)
*/
jbd2_journal_switch_revoke_table(journal);

+ write_lock(&journal->j_state_lock);
/*
* Reserved credits cannot be claimed anymore, free them
*/
atomic_sub(atomic_read(&journal->j_reserved_credits),
&commit_transaction->t_outstanding_credits);

- write_lock(&journal->j_state_lock);
trace_jbd2_commit_flushing(journal, commit_transaction);
stats.run.rs_flushing = jiffies;
stats.run.rs_locked = jbd2_time_diff(stats.run.rs_locked,
--
2.35.1