From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 44B1C46D0B7; Tue, 21 Jul 2026 18:16:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784657795; cv=none; b=lFAMCsGum/+l6ooQm256m1KMmtEZppuF65xWzHSr8SBtdZ+NVIyke3r0Pg7hbaj/Bu5lU6HXO/eG9VK3x4w8S4KvJwvS2+ApRY3eV/8CaZJe4RS2xCvVCC+JyMGfwKasNyomhpYrXt0/9k0T3V52NY4l/rvbAci5+hcfITYCnEM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784657795; c=relaxed/simple; bh=GAuUQsrvSBg/TM5BFy4NCWYiAEugEet2KQ0EJnCKPn4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ebFNqoLqy4AvZKbzoCqJCC5jYKd9+JPKF5KnLD5IWr3hn0dpajOWn4G31k0Km4hdn4KnVRA3SXsh5zeH0OpCjD7K9BbYAkHzQnJOa3YOaVl4iJcZDwZlTUBekUilzqnMBJBk1bvtusPqvmLQbUBtcIjYFUvqA+6Ng5o6RYeEDrs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=PfA7aKgV; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="PfA7aKgV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A9DA61F000E9; Tue, 21 Jul 2026 18:16:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784657794; bh=4UvgnMLkZCOEAeqXxiDr06M/UHrBkksjGPnQwKK3FqY=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=PfA7aKgVVCGn6ln/zXgC3ByR3mQ09hTCn+mfnCBT/tDoUg6OcsnN8PVRf2hzOgduR 7smyxsPwKcwuAkIifzQ35j4lTM3UcZupJ4y2FbJ63dzPJkZgx9zK8Th9d+NQK9tiV4 N4GykSx2T/5YMjVC4GR5KYmIYs+FvrgODL96eUSk= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Chen Cheng , Yu Kuai , Sasha Levin Subject: [PATCH 6.18 0900/1611] md/raid5: avoid R5_Overlap races while breaking stripe batches Date: Tue, 21 Jul 2026 17:16:56 +0200 Message-ID: <20260721152535.634317186@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260721152514.750365251@linuxfoundation.org> References: <20260721152514.750365251@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Chen Cheng [ Upstream commit 55b77337bdd088c77461588e5ec094421b89911b ] KCSAN report a race in break_stripe_batch_list() vs. raid5_make_request() on sh->dev[i].flags (plain word write vs. atomic bit op).. and .. one possible scenario is: CPU1 CPU2 break_stripe_batch_list(sh1) -> handle sh2 -> lock(sh2) -> sh2->batch_head = NULL -> unlock(sh2) -> test_and_clear_bit(R5_Overlap, sh2->dev[i].flags) -> wake_up_bit(sh2->dev[i].flags) raid5_make_request() -> add_all_stripe_bios(sh2) -> lock(sh2) -> stripe_bio_overlaps(sh2) returns true batch_head is NULL, so new bio overlap exist bio on sh2 -> true -> set_bit(R5_Overlap, sh2->dev[i].flags) -> unlock(sh2) -> wait_on_bit(sh2->dev[i].flags) -> sh2->dev[i].flags = sh1->dev[i].flags & ~R5_Overlap No wait_up_bit(), CPU2 could be wait_on_bit() forever... Fix by : - Expand the protect zone. - Use batch_head's device flag's snaphot when no held head_sh->stripe_lock. - Move sh/head_sh->batch_head = NULL to the end of protected zone , and , any concurrent add_all_stripe_bios() grabs sh->stripe_lock now either: - see batch_head != null, and , is rejected by stripe_bio_overlaps() under the lock (no R5_Overlap wait ) , or , - sees batch_head == NULL, only after dev[i].flags has already been set and the prior R5_Overlap waiters worken. KCSAN report: ================================================ BUG: KCSAN: data-race in break_stripe_batch_list / raid5_make_request write (marked) to 0xffff8e89c8117548 of 8 bytes by task 4042 on cpu 0: raid5_make_request+0xea0/0x2930 md_handle_request+0x4a2/0xa40 md_submit_bio+0x109/0x1a0 __submit_bio+0x2ec/0x390 submit_bio_noacct_nocheck+0x457/0x710 submit_bio_noacct+0x2a7/0xc20 submit_bio+0x56/0x250 blkdev_direct_IO+0x54c/0xda0 blkdev_write_iter+0x38f/0x570 aio_write+0x22b/0x490 io_submit_one+0xa51/0xf70 __x64_sys_io_submit+0xf7/0x220 x64_sys_call+0x1907/0x1c60 do_syscall_64+0x130/0x570 entry_SYSCALL_64_after_hwframe+0x76/0x7e read to 0xffff8e89c8117548 of 8 bytes by task 4010 on cpu 5: break_stripe_batch_list+0x249/0x480 handle_stripe_clean_event+0x720/0x9b0 handle_stripe+0x32fb/0x4500 handle_active_stripes.isra.0+0x6e0/0xa50 raid5d+0x7e0/0xba0 md_thread+0x15a/0x2d0 kthread+0x1e3/0x220 ret_from_fork+0x37a/0x410 ret_from_fork_asm+0x1a/0x30 value changed: 0x0000000000000019 -> 0x0000000000000099 --> R5_Overlap Fixes: fb642b92c267 ("md/raid5: duplicate some more handle_stripe_clean_event code in break_stripe_batch_list") Signed-off-by: Chen Cheng Link: https://patch.msgid.link/20260619041013.1207148-1-chencheng@fnnas.com Signed-off-by: Yu Kuai Signed-off-by: Sasha Levin --- drivers/md/raid5.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index e4cbf5fcec8e7a..b19d870e417194 100644 --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -4886,14 +4886,14 @@ static void break_stripe_batch_list(struct stripe_head *head_sh, sh->check_state = head_sh->check_state; sh->reconstruct_state = head_sh->reconstruct_state; spin_lock_irq(&sh->stripe_lock); - sh->batch_head = NULL; - spin_unlock_irq(&sh->stripe_lock); for (i = 0; i < sh->disks; i++) { if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags)) wake_up_bit(&sh->dev[i].flags, R5_Overlap); - sh->dev[i].flags = head_sh->dev[i].flags & + sh->dev[i].flags = READ_ONCE(head_sh->dev[i].flags) & (~((1 << R5_WriteError) | (1 << R5_Overlap))); } + sh->batch_head = NULL; + spin_unlock_irq(&sh->stripe_lock); state = READ_ONCE(sh->state); if (handle_flags == 0 || (state & handle_flags)) @@ -4901,11 +4901,11 @@ static void break_stripe_batch_list(struct stripe_head *head_sh, raid5_release_stripe(sh); } spin_lock_irq(&head_sh->stripe_lock); - head_sh->batch_head = NULL; - spin_unlock_irq(&head_sh->stripe_lock); for (i = 0; i < head_sh->disks; i++) if (test_and_clear_bit(R5_Overlap, &head_sh->dev[i].flags)) wake_up_bit(&head_sh->dev[i].flags, R5_Overlap); + head_sh->batch_head = NULL; + spin_unlock_irq(&head_sh->stripe_lock); state = READ_ONCE(head_sh->state); if (state & handle_flags) -- 2.53.0