From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 A768624467B; Tue, 22 Jul 2025 14:12:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753193563; cv=none; b=VWMnJeb/jRbikQus26mc3S3CoVe8n73EJ6uzpcFJUcOfQDrgM5o4gRPiixqCcf4Xvwhx7xeYZX0Jd1uklEjKQhHfzc5k1g0K/kiug8omQyu78/R4R4c16wzp4xHH8qZl9QmY4g/l21XW09YCkZXEhWyIWUgjTigynVbzP3WmwAE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753193563; c=relaxed/simple; bh=BYyAEZ2qB1uXZZGFtaCnoSYFfsaS+UyVDbJTb5LTT8g=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=SGFq2oqnhyie0f6ZxKca4tEiVf34nDSVp91KsEnVfzhmV0ibdjynEAJPNkFsgNujSR+v35CzMIvuZ6Xel9103TTBJHUm8Z8k5tsNuZ3qZsMzHartJ1gfZ4TMElCUOFzmiirkvtiUf0ojQjBMtFCHTSKu/xDqhS5VDVHwuci+3JY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=kAEvKp5h; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="kAEvKp5h" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2CDFBC4CEEB; Tue, 22 Jul 2025 14:12:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1753193563; bh=BYyAEZ2qB1uXZZGFtaCnoSYFfsaS+UyVDbJTb5LTT8g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kAEvKp5h9l73fQ4vG7qfH+b67Z+CKQLo2Hv5Qq+fzokHVk8jEEpxPHcFPcihRtLOJ PoITSa96x7XdoIbs+QUn+y6mlXruCc1tYvwrQ5uqexcisdes5SYGabO915SjCj8I4p RZf5Gi2XXuOmvDagHGTAhcDi4Zsw+9GurIQbW2TA= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Changhui Zhong , Ming Lei , Jens Axboe , Sasha Levin Subject: [PATCH 6.15 130/187] loop: use kiocb helpers to fix lockdep warning Date: Tue, 22 Jul 2025 15:45:00 +0200 Message-ID: <20250722134350.583988545@linuxfoundation.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250722134345.761035548@linuxfoundation.org> References: <20250722134345.761035548@linuxfoundation.org> User-Agent: quilt/0.68 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 6.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ming Lei [ Upstream commit c4706c5058a7bd7d7c20f3b24a8f523ecad44e83 ] The lockdep tool can report a circular lock dependency warning in the loop driver's AIO read/write path: ``` [ 6540.587728] kworker/u96:5/72779 is trying to acquire lock: [ 6540.593856] ff110001b5968440 (sb_writers#9){.+.+}-{0:0}, at: loop_process_work+0x11a/0xf70 [loop] [ 6540.603786] [ 6540.603786] but task is already holding lock: [ 6540.610291] ff110001b5968440 (sb_writers#9){.+.+}-{0:0}, at: loop_process_work+0x11a/0xf70 [loop] [ 6540.620210] [ 6540.620210] other info that might help us debug this: [ 6540.627499] Possible unsafe locking scenario: [ 6540.627499] [ 6540.634110] CPU0 [ 6540.636841] ---- [ 6540.639574] lock(sb_writers#9); [ 6540.643281] lock(sb_writers#9); [ 6540.646988] [ 6540.646988] *** DEADLOCK *** ``` This patch fixes the issue by using the AIO-specific helpers `kiocb_start_write()` and `kiocb_end_write()`. These functions are designed to be used with a `kiocb` and manage write sequencing correctly for asynchronous I/O without introducing the problematic lock dependency. The `kiocb` is already part of the `loop_cmd` struct, so this change also simplifies the completion function `lo_rw_aio_do_completion()` by using the `iocb` from the `cmd` struct directly, instead of retrieving the loop device from the request queue. Fixes: 39d86db34e41 ("loop: add file_start_write() and file_end_write()") Cc: Changhui Zhong Signed-off-by: Ming Lei Link: https://lore.kernel.org/r/20250716114808.3159657-1-ming.lei@redhat.com Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin --- drivers/block/loop.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index f8d136684109a..3999056877572 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -308,14 +308,13 @@ static void lo_complete_rq(struct request *rq) static void lo_rw_aio_do_completion(struct loop_cmd *cmd) { struct request *rq = blk_mq_rq_from_pdu(cmd); - struct loop_device *lo = rq->q->queuedata; if (!atomic_dec_and_test(&cmd->ref)) return; kfree(cmd->bvec); cmd->bvec = NULL; if (req_op(rq) == REQ_OP_WRITE) - file_end_write(lo->lo_backing_file); + kiocb_end_write(&cmd->iocb); if (likely(!blk_should_fake_timeout(rq->q))) blk_mq_complete_request(rq); } @@ -391,7 +390,7 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, } if (rw == ITER_SOURCE) { - file_start_write(lo->lo_backing_file); + kiocb_start_write(&cmd->iocb); ret = file->f_op->write_iter(&cmd->iocb, &iter); } else ret = file->f_op->read_iter(&cmd->iocb, &iter); -- 2.39.5