From: Jan Kara <jack@suse.cz>
To: Ted Tso <tytso@mit.edu>
Cc: <linux-ext4@vger.kernel.org>, Jan Kara <jack@suse.cz>,
syzbot+30774a6acf6a2cf6d535@syzkaller.appspotmail.com
Subject: [PATCH 1/2] ext4: Annotate data race in start_this_handle()
Date: Tue, 6 Apr 2021 18:17:59 +0200 [thread overview]
Message-ID: <20210406161804.20150-1-jack@suse.cz> (raw)
In-Reply-To: <20210406161605.2504-1-jack@suse.cz>
Access to journal->j_running_transaction is not protected by appropriate
lock and thus is racy. We are well aware of that and the code handles
the race properly. Just add a comment and data_race() annotation.
Reported-by: syzbot+30774a6acf6a2cf6d535@syzkaller.appspotmail.com
Signed-off-by: Jan Kara <jack@suse.cz>
---
fs/jbd2/transaction.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 9396666b7314..398d1d9209e2 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -349,7 +349,12 @@ static int start_this_handle(journal_t *journal, handle_t *handle,
}
alloc_transaction:
- if (!journal->j_running_transaction) {
+ /*
+ * This check is racy but it is just an optimization of allocating new
+ * transaction early if there are high chances we'll need it. If we
+ * guess wrong, we'll retry or free unused transaction.
+ */
+ if (!data_race(journal->j_running_transaction)) {
/*
* If __GFP_FS is not present, then we may be being called from
* inside the fs writeback layer, so we MUST NOT fail.
--
2.26.2
next prev parent reply other threads:[~2021-04-06 16:18 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-06 16:17 [PATCH 0/2] ext4: Annotate two harmless KCSAN data races Jan Kara
2021-04-06 16:17 ` Jan Kara [this message]
2021-04-10 1:24 ` [PATCH 1/2] ext4: Annotate data race in start_this_handle() Theodore Ts'o
2021-04-06 16:18 ` [PATCH 2/2] ext4: Annotate data race in jbd2_journal_dirty_metadata() Jan Kara
2021-04-10 1:24 ` Theodore Ts'o
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