From patchwork Sat Mar 8 17:47:38 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ignacio Encinas X-Patchwork-Id: 14007600 Received: from out-184.mta0.migadu.com (out-184.mta0.migadu.com [91.218.175.184]) (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 95F68AD4B for ; Sat, 8 Mar 2025 17:47:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.184 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741456077; cv=none; b=GSWLhdFqRXLt4g+JEL2Hzhx8KDOAVTljJtQZEb+ndfVWQP2o3Sdz74YV3o/6UqGW0xYHrrprOXqZmwl5cvw7ndYLD57NHIAdYThH1g1gFJaiRmrSSPr7amP/kE9vHJgESHcqyGjBH3o4AiSs4tiqv22W4BSCzjOsGsH0E2XdOTc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741456077; c=relaxed/simple; bh=p6InFRndnQU8EQckgN3pPyd05sWUsTAd05gohqs9UvY=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:To:Cc; b=jX5OmMlWPVtDUCId4Bxdcw5wRWqC6FZ/N0W4jKJM01faZCsO95qOiQpP2hjUHBL8GSWR4WMaJekRcn2qZ5iLMjAE4LmxQg0oSmw+1xAJTI5gw1IrKCXuARtAh2vQU2DVdA/qmwdQL6ESYO+5CNDARfJEEbJsmnPGmo4KLuC1Ytw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=iencinas.com; spf=pass smtp.mailfrom=iencinas.com; dkim=pass (2048-bit key) header.d=iencinas.com header.i=@iencinas.com header.b=O9hBrwsU; arc=none smtp.client-ip=91.218.175.184 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=iencinas.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=iencinas.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=iencinas.com header.i=@iencinas.com header.b="O9hBrwsU" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=iencinas.com; s=key1; t=1741456072; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=iH+nG+xkzMrLIyIs8nUbB7bGFwyHx+ZLku2SBIZQKbo=; b=O9hBrwsUnzHE6nP8M7rR4LwDxH1racbMlTbDUxI6kt28RSBISHSGjPuqHN37y1AL9R5XmB KOkUSNNUTpalDqEGN3U7KJmovY0GMKzAJjOfnV4Whz/s+gAfEtlgykMaJCMyFw5k1VBPyh z6Ip+bhfw1m3qzFP7qw50PQrsCmyQ+5u4R80qdViQNzdfrLFE5vW/OEquCyzBb62MPNveJ FqHqNBIBwdZVBfEVuXMDr3oUKg9KCbggJ+rKvxsh1aA543ai7EY4R3hgKnqvKjAJT45/8l f7+rPrObKiw+ri8IP8BWRSu56arZgDZ8D9Xrwuf4uGM63B0dQKAr3rHPhn08Kg== From: Ignacio Encinas Date: Sat, 08 Mar 2025 18:47:38 +0100 Subject: [PATCH] 9p/trans_fd: mark concurrent read and writes to p9_conn->err Precedence: bulk X-Mailing-List: v9fs@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20250308-p9_conn_err_benign_data_race-v1-1-729e57d5832b@iencinas.com> X-B4-Tracking: v=1; b=H4sIALmCzGcC/x3MTQrCMBAG0KuUWRuIkWLqVUSG/HxtZzMtExGh9 O4Gl2/zDmowQaPHcJDhI0027bheBipr0gVOajcFH0Z/89HtE5dNlWHGGSqLck3vxJYKXLiPcUb MGdVTL3bDLN9//3yd5w/NHJ9gbgAAAA== X-Change-ID: 20250308-p9_conn_err_benign_data_race-2758fe8bbed0 To: linux-kernel-mentees@lists.linux.dev, skhan@linuxfoundation.org, Eric Van Hensbergen , Latchesar Ionkov , Dominique Martinet , Christian Schoenebeck Cc: Sishuai Gong , Marco Elver , v9fs@lists.linux.dev, linux-kernel@vger.kernel.org, syzbot+d69a7cc8c683c2cb7506@syzkaller.appspotmail.com, syzbot+483d6c9b9231ea7e1851@syzkaller.appspotmail.com, Ignacio Encinas X-Migadu-Flow: FLOW_OUT Writes for the error value of a connection are spinlock-protected inside p9_conn_cancel, but lockless reads are present elsewhere to avoid performing unnecessary work after an error has been met. Mark the write and lockless reads to make KCSAN happy. Mark the write as exclusive following the recommendation in "Lock-Protected Writes with Lockless Reads" in tools/memory-model/Documentation/access-marking.txt while we are at it. Reported-by: syzbot+d69a7cc8c683c2cb7506@syzkaller.appspotmail.com Reported-by: syzbot+483d6c9b9231ea7e1851@syzkaller.appspotmail.com Signed-off-by: Ignacio Encinas --- Hello! I noticed these syzbot reports that seem to repeat periodically and figured I should send a patch. The read-paths look very similar to the one changed here [1]. Perhaps it would make sense to make them the same? [1] https://lore.kernel.org/all/ZTZtHdqifXlWG8nN@codewreck.org/ --- net/9p/trans_fd.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) --- base-commit: 2a520073e74fbb956b5564818fc5529dcc7e9f0e change-id: 20250308-p9_conn_err_benign_data_race-2758fe8bbed0 Best regards, diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c index 196060dc6138af10e99ad04a76ee36a11f770c65..5458e6530084cabeb01d13e9b9a4b1b8f338e494 100644 --- a/net/9p/trans_fd.c +++ b/net/9p/trans_fd.c @@ -196,7 +196,8 @@ static void p9_conn_cancel(struct p9_conn *m, int err) return; } - m->err = err; + WRITE_ONCE(m->err, err); + ASSERT_EXCLUSIVE_WRITER(m->err); list_for_each_entry_safe(req, rtmp, &m->req_list, req_list) { list_move(&req->req_list, &cancel_list); @@ -283,7 +284,7 @@ static void p9_read_work(struct work_struct *work) m = container_of(work, struct p9_conn, rq); - if (m->err < 0) + if (READ_ONCE(m->err) < 0) return; p9_debug(P9_DEBUG_TRANS, "start mux %p pos %zd\n", m, m->rc.offset); @@ -450,7 +451,7 @@ static void p9_write_work(struct work_struct *work) m = container_of(work, struct p9_conn, wq); - if (m->err < 0) { + if (READ_ONCE(m->err) < 0) { clear_bit(Wworksched, &m->wsched); return; } @@ -622,7 +623,7 @@ static void p9_poll_mux(struct p9_conn *m) __poll_t n; int err = -ECONNRESET; - if (m->err < 0) + if (READ_ONCE(m->err) < 0) return; n = p9_fd_poll(m->client, NULL, &err); @@ -673,7 +674,7 @@ static int p9_fd_request(struct p9_client *client, struct p9_req_t *req) spin_lock(&m->req_lock); - if (m->err < 0) { + if (READ_ONCE(m->err) < 0) { spin_unlock(&m->req_lock); return m->err; }