From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f201.google.com (mail-pg1-f201.google.com [209.85.215.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 63F3540DFCC for ; Thu, 7 May 2026 05:51:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778133102; cv=none; b=p52iBQAZJH71hYVW7nvZ3wGgmjXKn4NFC9XR0qI0HLEatf1gMBMtb16cMvV8AOPy+DrJvuXaB/R3Qbwy+q8FxmGmKst/ChPzxIXqZLFspEDCzdkGVk375t+7uwXwHhfsNOSKn0jR0sUIeLSThWl+iSfyPxqHG/9zRHYHvYBXrR0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778133102; c=relaxed/simple; bh=jspcJ+XGVtmcJoLA2b6dVBoyp7lmH5gwX62B+Q0P7Ig=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=nzASfzZ2zSNuCz/tWmXbhDxDB7Zcvgits5H0oCzaBAB3M2i41eelaE/EGDaOX0CN/A5u5BIy14PY5i9LINulos9DSf4S8KITic5YkZwyfDRqhCF5+rQW9wBDZvUPLIwjnLKHFjaDJtagCXlybuBFHfc32R7r+G5X7Notvg/CLTk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--joonwonkang.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=IV2xAIQX; arc=none smtp.client-ip=209.85.215.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--joonwonkang.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="IV2xAIQX" Received: by mail-pg1-f201.google.com with SMTP id 41be03b00d2f7-c798fc1a426so305249a12.2 for ; Wed, 06 May 2026 22:51:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1778133101; x=1778737901; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=MYuyuGpque6//gGJu9ipQm1QDza51zuHMLqXnZVgYuA=; b=IV2xAIQXEwbVcrLP69/o8tKAYXAXrlsLiNkjmDlX0Q+PRAJhCYvFv2i8kOGneA7H+J Kh4BdujkBEXd9DDFSIxQ3rLAnE9qYkOUN+AkO6EwQoh+v2J8gRpJL8PvbxtNX0tlfGW4 Bch0DpJ81U4A99MM07xN6g3s9K59RoL42g/WobM7GCB049nIhUN1c2OSdhnVBjTHHCxA xc66EF9VkFeF2ztjbIB7EuCuMFf2q0RpsdvUaMnx1TzBFqy2o00rtHkI5RKwSUp0b96i jpWIq7jGb6T3Mne77JX7gOjdln6gHf8bWZNMPub0hewvKNnA918+7S4uU/dVPmikIZaJ McMw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1778133101; x=1778737901; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=MYuyuGpque6//gGJu9ipQm1QDza51zuHMLqXnZVgYuA=; b=iymzj+eXyfz0lD6Jph5Qsfk14Gjb/D3u1OgROUkRF0SplpGjMhycv4MbGPgDkNtgZQ k8l4S3eqWt4LFxTv0ZdqR95A564hx5mTVlFkjkwjq9+p0guo3DM5e7pnIc21aDhSFchG tiqzjXrZnTz9BhIsW2LDxzM7uVCdko9KdbNElzTYqXeHNytwLLiwuSfxa+EFVEvlKZOc SORejcMt9Z8AsIIgk8iaPBzHNmSk7X0ud1FvrUsw7Pb3vaKquuM6omndDAeAxblT9BA3 hBlcDoAcRfOku2kuw1SfK1MF68rj5XJBDQf5Av+e/vjlDRNyFDjsEH2ELmzL2J5arXJP yfOw== X-Forwarded-Encrypted: i=1; AFNElJ/OyRWr7YsDLNHNblsdnbX++/C++5gUNCBWT+n/Scs4jBXIhDYmHVtzXLv5fouNg++CegJwZpqqx7S7DCs=@vger.kernel.org X-Gm-Message-State: AOJu0Yzys48XwA585mLiEcxrF1LW5ZEmFmBvyOoB1QNRuHg8ByboVfE2 Ol83L7OEPWvMcLClp/dX805TrakEf59T7X2bD2itpYaWjNHOO7LiLR6akg8ckBcd90YvhgjqINj xh7huUFnZbU387Fjwtwg0o4vgsg== X-Received: from pgbbj25.prod.google.com ([2002:a05:6a02:199:b0:c7b:b2bd:6cb]) (user=joonwonkang job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:94c7:b0:39c:14b3:6234 with SMTP id adf61e73a8af0-3aa5a86e53dmr6933824637.15.1778133100373; Wed, 06 May 2026 22:51:40 -0700 (PDT) Date: Thu, 7 May 2026 05:51:17 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.54.0.545.g6539524ca2-goog Message-ID: <20260507055117.2466957-1-joonwonkang@google.com> Subject: [PATCH 6.12.y] mailbox: Fix NULL message support in mbox_send_message() From: Joonwon Kang To: stable@vger.kernel.org, jassisinghbrar@gmail.com Cc: thierry.reding@gmail.com, jonathanh@nvidia.com, linux-kernel@vger.kernel.org, linux-tegra@vger.kernel.org, joonwonkang@google.com, Douglas Anderson Content-Type: text/plain; charset="UTF-8" From: Jassi Brar commit c58e9456e30c ("mailbox: Fix NULL message support in mbox_send_message()") upstream. The active_req field serves double duty as both the "is a TX in flight" flag (NULL means idle) and the storage for the in-flight message pointer. When a client sends NULL via mbox_send_message(), active_req is set to NULL, which the framework misinterprets as "no active request". This breaks the TX state machine by: - tx_tick() short-circuits on (!mssg), skipping the tx_done callback and the tx_complete completion - txdone_hrtimer() skips the channel entirely since active_req is NULL, so poll-based TX-done detection never fires. Fix this by introducing a MBOX_NO_MSG sentinel value that means "no active request," freeing NULL to be valid message data. The sentinel is defined in the subsystem-internal mailbox.h so that controller drivers within drivers/mailbox/ can reference it, but it is not exposed to clients outside the subsystem. Fifteen in-tree callers send NULL (doorbell-style IPCs on Qualcomm, Tegra, TI, Xilinx, i.MX, SCMI, and PCC platforms). All were audited for regression: - Most already work around the bug via knows_txdone=true with a manual mbox_client_txdone() call, making the framework's tracking irrelevant. These are unaffected. - Poll-based callers (Xilinx zynqmp/r5) are strictly better off: the poll timer now correctly detects NULL-active channels instead of silently skipping them. - irq-qcom-mpm.c was a pre-existing bug -- the only Qualcomm caller that omitted the knows_txdone + mbox_client_txdone() pattern. Fixed in a companion commit ("irqchip/qcom-mpm: Fix missing mailbox TX done acknowledgment"). - No caller sets both a tx_done callback and sends NULL, nor combines tx_block=true with NULL sends, so the newly reachable callback/completion paths are never exercised. Also update tegra-hsp's flush callback, which directly inspects active_req to wait for the channel to drain: the old "!= NULL" check becomes "!= MBOX_NO_MSG", otherwise flush spins until timeout since the sentinel is non-NULL. The only tradeoff is that 'MBOX_NO_MSG' can not be used as a message by clients. Reported-by: Joonwon Kang Reviewed-by: Douglas Anderson Signed-off-by: Jassi Brar Signed-off-by: Joonwon Kang --- drivers/mailbox/mailbox.c | 15 ++++++++------- drivers/mailbox/tegra-hsp.c | 2 +- include/linux/mailbox_controller.h | 3 +++ 3 files changed, 12 insertions(+), 8 deletions(-) diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c index d3d26a2c9895..aee552a2fbc7 100644 --- a/drivers/mailbox/mailbox.c +++ b/drivers/mailbox/mailbox.c @@ -60,7 +60,7 @@ static void msg_submit(struct mbox_chan *chan) spin_lock_irqsave(&chan->lock, flags); - if (!chan->msg_count || chan->active_req) + if (!chan->msg_count || chan->active_req != MBOX_NO_MSG) goto exit; count = chan->msg_count; @@ -98,13 +98,13 @@ static void tx_tick(struct mbox_chan *chan, int r) spin_lock_irqsave(&chan->lock, flags); mssg = chan->active_req; - chan->active_req = NULL; + chan->active_req = MBOX_NO_MSG; spin_unlock_irqrestore(&chan->lock, flags); /* Submit next message */ msg_submit(chan); - if (!mssg) + if (mssg == MBOX_NO_MSG) return; /* Notify the client */ @@ -126,7 +126,7 @@ static enum hrtimer_restart txdone_hrtimer(struct hrtimer *hrtimer) for (i = 0; i < mbox->num_chans; i++) { struct mbox_chan *chan = &mbox->chans[i]; - if (chan->active_req && chan->cl) { + if (chan->active_req != MBOX_NO_MSG && chan->cl) { txdone = chan->mbox->ops->last_tx_done(chan); if (txdone) tx_tick(chan, 0); @@ -258,7 +258,7 @@ int mbox_send_message(struct mbox_chan *chan, void *mssg) { int t; - if (!chan || !chan->cl) + if (!chan || !chan->cl || mssg == MBOX_NO_MSG) return -EINVAL; t = add_to_rbuf(chan, mssg); @@ -332,7 +332,7 @@ static int __mbox_bind_client(struct mbox_chan *chan, struct mbox_client *cl) spin_lock_irqsave(&chan->lock, flags); chan->msg_free = 0; chan->msg_count = 0; - chan->active_req = NULL; + chan->active_req = MBOX_NO_MSG; chan->cl = cl; init_completion(&chan->tx_complete); @@ -485,7 +485,7 @@ void mbox_free_channel(struct mbox_chan *chan) /* The queued TX requests are simply aborted, no callbacks are made */ spin_lock_irqsave(&chan->lock, flags); chan->cl = NULL; - chan->active_req = NULL; + chan->active_req = MBOX_NO_MSG; if (chan->txdone_method == TXDONE_BY_ACK) chan->txdone_method = TXDONE_BY_POLL; @@ -545,6 +545,7 @@ int mbox_controller_register(struct mbox_controller *mbox) chan->cl = NULL; chan->mbox = mbox; + chan->active_req = MBOX_NO_MSG; chan->txdone_method = txdone; spin_lock_init(&chan->lock); } diff --git a/drivers/mailbox/tegra-hsp.c b/drivers/mailbox/tegra-hsp.c index 19ef56cbcfd3..7a422d563948 100644 --- a/drivers/mailbox/tegra-hsp.c +++ b/drivers/mailbox/tegra-hsp.c @@ -487,7 +487,7 @@ static int tegra_hsp_mailbox_flush(struct mbox_chan *chan, mbox_chan_txdone(chan, 0); /* Wait until channel is empty */ - if (chan->active_req != NULL) + if (chan->active_req != MBOX_NO_MSG) continue; return 0; diff --git a/include/linux/mailbox_controller.h b/include/linux/mailbox_controller.h index 6fee33cb52f5..fa5020262dda 100644 --- a/include/linux/mailbox_controller.h +++ b/include/linux/mailbox_controller.h @@ -11,6 +11,9 @@ struct mbox_chan; +/* Sentinel value distinguishing "no active request" from "NULL message data" */ +#define MBOX_NO_MSG ((void *)-1) + /** * struct mbox_chan_ops - methods to control mailbox channels * @send_data: The API asks the MBOX controller driver, in atomic -- 2.54.0.545.g6539524ca2-goog