From patchwork Thu Mar 13 18:08:19 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ignacio Encinas X-Patchwork-Id: 14015730 Received: from out-170.mta1.migadu.com (out-170.mta1.migadu.com [95.215.58.170]) (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 A68471E9B26 for ; Thu, 13 Mar 2025 18:08:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.170 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741889325; cv=none; b=AhZDfJnnERaw0IpbPyjpU2wbrxvyGkJ5/YiPHsT1hkADdC4pFZ53RvMzw0p6eaCoYUxlPrUSKmWasXpOqMn59Ezdgvj5QfYEtqj7YyeroUZRJ2P0v6Ih/BW49Z/5yUq1iHaWBXpx+/WmCq+OLsJBbF5nzz+tBJ6DEx3dU0MdDPc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741889325; c=relaxed/simple; bh=MXtePF6repqds/x6JPCzOwKs4bPaXnVnBSNXtX5OfIc=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:To:Cc; b=MfWcvEHXrH9z2WQSduShKi48TT7ZLxqXFvBTmDkg8nzp/01/2e8DHHekNCb4FZs70uzBWaBPXDCvfYM/2zMNSsJigRlEUCXLoKIrgC0Mv9LhA+kKgJBJkxqR/BzgGtue1xT9kYYeEKp246tZw0xYVpfbfx9Tx8o3to2Ppm4Hqvg= 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=Ao39xEo/; arc=none smtp.client-ip=95.215.58.170 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="Ao39xEo/" 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=1741889320; 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=oWH7hszwO9I5RYZpht/nXn68Y2cBdPRRedslDcO5mD8=; b=Ao39xEo/pSp/j5tAL4U5bRkiqX/8hAJD2h5Q3TQYeoM2KfRkAZOXysg68TccSm87i+b8UV kiREpjW7qU6Qz5NKsUVUQSnyPRUNScPmTvRmGLrA0zOQMJD51uK13Ub6Bq8SXcopsvd1VE 7p3Zn+BdFU4Rjarkxrw6vR2AaFmrOwPBr8UlVsv32H+n6YPJ04zzwb7xuKMCLJB9l4PWdZ yBjQeWsgIXA8Fjn6KqCNIcpPA+5z0Y4LVRZ40AMGel90Z5xTXaDVtGl8rqS+TEXPS+AHHF K4lghj57TDh/oo+B50iD8d9RL/q4sqoc1cB84Av2UH7VZRWeFsP3gjRg8Pw/UA== From: Ignacio Encinas Date: Thu, 13 Mar 2025 19:08:19 +0100 Subject: [PATCH v2] 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: <20250313-p9_conn_err_benign_data_race-v2-1-0bb9f45f6bb2@iencinas.com> X-B4-Tracking: v=1; b=H4sIABIf02cC/43NTQqDMBCG4atI1k2JkWDsqvcoEvIz6iw6KRORF vHuTT1Bl8+3eL9dFGCEIm7NLhg2LJipQl8aERdPM0hM1UIrbVSnrHwNLmYiB8wuAOFMLvnVO/Y RpO6NncCGAEmJmngxTPg+84+xesGyZv6cb1v7W/8Mb61sZa8HMH0yttPhjkARyZdrzE8xHsfxB eL3bFzLAAAA 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 --- Changes in v2: Drop unnecessary READ_ONCE in p9_fd_request (that I added in v1) -@@ net/9p/trans_fd.c: 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; - } - Link to v1: https://lore.kernel.org/r/20250308-p9_conn_err_benign_data_race-v1-1-729e57d5832b@iencinas.com --- net/9p/trans_fd.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 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..758eaeddf32b480e0a88914da66f923f7021e608 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);