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 36AB23FD12E for ; Mon, 15 Jun 2026 15:21:31 +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=1781536892; cv=none; b=qk93tfMlX+OkcWLqNM1m4vqvIDePW7CYPLnhfIYaF3P1I0h2NMol94ARqjw7YGa8Hqyc4hF/ZmtpmipZsIG35+Utf/Ljaz89tzyGcS2+9mycbbGngix7cxV49AKWunzoweOHNzyZCWK2DLBkru/aMbvOe1lVitVgM1l34UHe9UA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781536892; c=relaxed/simple; bh=K/XYJLofJ1w5vHoV5Gk+HlOI6cb4DoIdVW+WqVKgfCs=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=WNzCGhWz1/o6mmwCrdj4wiTVYuNrOqXP3fwB8x/aMv0qNoDYOoTHDoD17pXfydGmQS6GXWCx8+MKV3CeXZA2r84lCidJpKXyycp50ppWiSu/tVtQW1hIqz0tHvMtSDAb441tmVLXaj22UuMsCZFZYrvHOiNjJXpgUJvPzs2bo20= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Ag9e623f; 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="Ag9e623f" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 415031F000E9; Mon, 15 Jun 2026 15:21:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1781536891; bh=F6hC0NaV/r/Fk1KRrBolEwfnbbO6frbhmWSln22rSpg=; h=Subject:To:Cc:From:Date; b=Ag9e623ftlhGMwZlEIDHZL2kcjDnUWkrmYFULFQ8OYnQdIybi45y01fOZ7Tuq2CnX 0/yCFXyKzdljo31zidXGvpQfXCezz0Vz/fDgsQhgJWgu/orvYRePVZzMW1mRU43usg JE/khj5Rtb6oYyOCwccVHlBCgGQK0JMLhVBSeY+4= Subject: FAILED: patch "[PATCH] firmware: samsung: acpm: Fix infinite loop on sequence number" failed to apply to 7.0-stable tree To: tudor.ambarus@linaro.org,krzk@kernel.org Cc: From: Date: Mon, 15 Jun 2026 16:49:42 +0200 Message-ID: <2026061542-daintily-knickers-a496@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 7.0-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-7.0.y git checkout FETCH_HEAD git cherry-pick -x 7fe40c32a33905302341797b5d12c541729dd08d # git commit -s git send-email --to '' --in-reply-to '2026061542-daintily-knickers-a496@gregkh' --subject-prefix 'PATCH 7.0.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 7fe40c32a33905302341797b5d12c541729dd08d Mon Sep 17 00:00:00 2001 From: Tudor Ambarus Date: Tue, 5 May 2026 13:13:04 +0000 Subject: [PATCH] firmware: samsung: acpm: Fix infinite loop on sequence number exhaustion Sashiko identified a possible infinite loop [1]. ACPM IPC sequence numbers are tracked via a 64-bit bitmap. Previously, acpm_prepare_xfer() used a do...while loop to search for a free sequence number. If all 63 available sequence numbers are leaked due to transient hardware timeouts or mailbox failures, the bitmap becomes full. The next call to acpm_prepare_xfer() would enter an infinite loop. Fix this by utilizing the kernel's optimized bitmap search functions (find_next_zero_bit / find_first_zero_bit). If the pool is completely exhausted, log the failure and return -EBUSY to allow the kernel to fail gracefully instead of hanging. Furthermore, drop the allocation loop entirely. Because acpm_prepare_xfer() is strictly called under the 'tx_lock' mutex, sequence number allocations are perfectly serialized. If find_next_zero_bit() locates a free bit, a single test_and_set_bit_lock() is mathematically guaranteed to succeed. To enforce this locking invariant, wrap the allocation in a WARN_ON_ONCE. If the atomic set fails, it indicates the driver's mutex serialization is fundamentally broken. The warning generates a stack trace for debugging, while returning -EIO immediately aborts the transfer to prevent silent payload corruption. Cc: stable@vger.kernel.org Fixes: a88927b534ba ("firmware: add Exynos ACPM protocol driver") Closes: https://sashiko.dev/#/patchset/20260420-acpm-tmu-v3-0-3dc8e93f0b26%40linaro.org [1] Signed-off-by: Tudor Ambarus Link: https://patch.msgid.link/20260505-acpm-fixes-sashiko-reports-v5-7-43b5ee7f1674@linaro.org Signed-off-by: Krzysztof Kozlowski diff --git a/drivers/firmware/samsung/exynos-acpm.c b/drivers/firmware/samsung/exynos-acpm.c index 3fa9fe283be4..19db3674a28f 100644 --- a/drivers/firmware/samsung/exynos-acpm.c +++ b/drivers/firmware/samsung/exynos-acpm.c @@ -12,6 +12,7 @@ #include #include #include +#include #include #include #include @@ -390,34 +391,48 @@ static int acpm_wait_for_queue_slots(struct acpm_chan *achan, u32 next_tx_front) * TX queue. * @achan: ACPM channel info. * @xfer: reference to the transfer being prepared. + * + * Return: 0 on success, -errno otherwise. */ -static void acpm_prepare_xfer(struct acpm_chan *achan, - const struct acpm_xfer *xfer) +static int acpm_prepare_xfer(struct acpm_chan *achan, + const struct acpm_xfer *xfer) { struct acpm_rx_data *rx_data; u32 *txd = (u32 *)xfer->txd; + unsigned long size = ACPM_SEQNUM_MAX - 1; + unsigned long bit = achan->seqnum; + + bit = find_next_zero_bit(achan->bitmap_seqnum, size, bit); + if (bit >= size) { + bit = find_first_zero_bit(achan->bitmap_seqnum, size); + if (bit >= size) { + dev_err_ratelimited(achan->acpm->dev, + "ACPM sequence number pool exhausted\n"); + return -EBUSY; + } + } /* - * Prevent chan->seqnum from being re-used. - * test_and_set_bit_lock() provides formal LKMM Acquire semantics. - * It pairs with the RX thread's clear_bit_unlock() to ensure the CPU - * does not speculatively execute the rx_data buffer wipe (memset) - * before the sequence number is safely claimed. + * Execute the atomic set to formally claim the bit and establish + * LKMM Acquire semantics against the RX thread's clear_bit_unlock(). + * A loop is unnecessary because allocations are strictly serialized + * by tx_lock. */ - do { - if (++achan->seqnum == ACPM_SEQNUM_MAX) - achan->seqnum = 1; - /* Flag the index based on seqnum. (seqnum: 1~63, bitmap: 0~62) */ - } while (test_and_set_bit_lock(achan->seqnum - 1, achan->bitmap_seqnum)); + if (WARN_ON_ONCE(test_and_set_bit_lock(bit, achan->bitmap_seqnum))) + return -EIO; + /* Flag the index based on seqnum. (seqnum: 1~63, bitmap: 0~62) */ + achan->seqnum = bit + 1; txd[0] |= FIELD_PREP(ACPM_PROTOCOL_SEQNUM, achan->seqnum); /* Clear data for upcoming responses */ - rx_data = &achan->rx_data[achan->seqnum - 1]; + rx_data = &achan->rx_data[bit]; rx_data->completed = false; memset(rx_data->cmd, 0, sizeof(*rx_data->cmd) * rx_data->n_cmd); /* zero means no response expected */ rx_data->rxcnt = xfer->rxcnt; + + return 0; } /** @@ -477,7 +492,9 @@ int acpm_do_xfer(struct acpm_handle *handle, const struct acpm_xfer *xfer) if (ret) return ret; - acpm_prepare_xfer(achan, xfer); + ret = acpm_prepare_xfer(achan, xfer); + if (ret) + return ret; /* Write TX command. */ __iowrite32_copy(achan->tx.base + achan->mlen * tx_front,