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 F31AE288CB7; Fri, 6 Jun 2025 15:44:36 +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=1749224677; cv=none; b=k59api/5joUWKiWrVI/M6OEOdWO8dkGvog4rCo4BCzw8s6DkF2bbXO5keXHznvoxq14wx8pQCCkorvWa1ZoDy59EBO9Ft2tdb5F1loNsAXsTtghRPN5eqpoe/8rlWXiRSoUqY6j3q96JIVxwv+tjXLYIqZQ+szx0xqNFvSUgHP8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749224677; c=relaxed/simple; bh=4hZWSSBiBmXgCZRjHUQHX6vSbzo+EvjVtjI/uIdFtzg=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=nW1vS6bHMnTWys2YOrB8ecQigEclYimuNTa7rwpUPz7hYZ8SHsaSwzftaaozYT24j2m61Z1W9YGg74XDHNl4CCACfPeTk5WSK1Xg6LA/imu3fC/BgBafSCc94zRB/i3t483EuVsgTPOQFxl/ivstd8KzQVFPjDfd+si+5bq/8Yc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pGqFH4ZL; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="pGqFH4ZL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 12CD5C4CEF0; Fri, 6 Jun 2025 15:44:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1749224676; bh=4hZWSSBiBmXgCZRjHUQHX6vSbzo+EvjVtjI/uIdFtzg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=pGqFH4ZLFN96FnGqa80FLFze15Fnb7Lv+LiHilorHz0kgobniy+su4n/3P/fnfoU8 myTeLm+6UK4RzQUUGCcKB1aWt0OkjKehTEqc70YAzeMJp1QPYNBxZQo0JPuV1irRH2 exMdKfPqik7bpsRFrodUQWxwQWZdqSiCCDbW34Uc0XtREMMcjQDSeDulw5Vt6h6XMh rGVGdsY2j1U+JA5sQn9xBhod0Mqk2W8dh2MA2/e3igJfctJLqkJrBYiTl0P0f8s0BV BrDN6IEwyjemnkUGd206BJf0/0HVVAijXSV/QZJvDN98iouFQLFplqMXSn2q/SyRme xILYqNGzOCjUw== From: Sasha Levin To: patches@lists.linux.dev, stable@vger.kernel.org Cc: Peng Fan , Jassi Brar , Sasha Levin , linux-kernel@vger.kernel.org Subject: [PATCH AUTOSEL 5.4 2/3] mailbox: Not protect module_put with spin_lock_irqsave Date: Fri, 6 Jun 2025 11:44:31 -0400 Message-Id: <20250606154433.548697-2-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250606154433.548697-1-sashal@kernel.org> References: <20250606154433.548697-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 5.4.294 Content-Transfer-Encoding: 8bit From: Peng Fan [ Upstream commit dddbd233e67e792bb0a3f9694a4707e6be29b2c6 ] &chan->lock is not supposed to protect 'chan->mbox'. And in __mbox_bind_client, try_module_get is also not protected by &chan->lock. So move module_put out of the lock protected region. Signed-off-by: Peng Fan Signed-off-by: Jassi Brar Signed-off-by: Sasha Levin --- **YES** This commit should be backported to stable kernel trees. **Analysis:** 1. **Clear Bug Fix**: The commit fixes an improper use of `module_put()` under a spinlock in `mbox_free_channel()`. Looking at the current code in `/home/sasha/linux/drivers/mailbox/mailbox.c:489`, `module_put()` is called while holding `&chan->lock` with `spin_lock_irqsave()`. 2. **Locking Inconsistency**: The commit message correctly identifies that `&chan->lock` is not supposed to protect `chan->mbox`. In `__mbox_bind_client()` (line 324), `try_module_get(chan->mbox->dev->driver->owner)` is called **outside** the spinlock protection, making the current `module_put()` placement inconsistent. 3. **Minimal Risk Change**: The fix is extremely simple and low-risk - it just moves one line (`module_put()`) outside the spinlock region. This maintains the same operation order but fixes the locking issue. 4. **No Side Effects**: Moving `module_put()` outside the lock doesn't change the functionality or introduce new race conditions. The `module_put()` implementation uses `atomic_dec_if_positive()`, so it's safe to call without additional locking. 5. **Follows Stable Rules**: This commit: - Fixes a real locking issue that could potentially cause problems - Is small and contained (single line move) - Has minimal regression risk - Doesn't introduce new features or architectural changes 6. **Similar Pattern**: Looking at similar commits in the historical references, commits that fix locking issues (like Similar Commit #5 which fixed a locking bug in mailbox-test) were marked as YES for backporting. The commit addresses a legitimate kernel locking violation where `module_put()` should not be called under a spinlock, making it a suitable candidate for stable tree backporting. drivers/mailbox/mailbox.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c index 6f54501dc7762..cb31ad917b352 100644 --- a/drivers/mailbox/mailbox.c +++ b/drivers/mailbox/mailbox.c @@ -459,8 +459,8 @@ void mbox_free_channel(struct mbox_chan *chan) if (chan->txdone_method == TXDONE_BY_ACK) chan->txdone_method = TXDONE_BY_POLL; - module_put(chan->mbox->dev->driver->owner); spin_unlock_irqrestore(&chan->lock, flags); + module_put(chan->mbox->dev->driver->owner); } EXPORT_SYMBOL_GPL(mbox_free_channel); -- 2.39.5