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[91.43.71.234]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43970d3ff6dsm36540108f8f.25.2026.02.25.07.38.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 25 Feb 2026 07:38:35 -0800 (PST) Message-ID: <1f1bbab1-b67c-4a5d-a88b-2c9b9f0970a2@googlemail.com> Date: Wed, 25 Feb 2026 16:38:34 +0100 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Betterbird (Windows) Subject: Re: [PATCH 6.19 000/781] 6.19.4-rc1 review To: Greg Kroah-Hartman , stable@vger.kernel.org Cc: patches@lists.linux.dev, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, linux@roeck-us.net, shuah@kernel.org, patches@kernelci.org, lkft-triage@lists.linaro.org, pavel@nabladev.com, jonathanh@nvidia.com, f.fainelli@gmail.com, sudipm.mukherjee@gmail.com, rwarsow@gmx.de, conor@kernel.org, hargar@microsoft.com, broonie@kernel.org, achill@achill.org, sr@sladewatkins.com References: <20260225012359.695468795@linuxfoundation.org> Content-Language: de-DE From: Peter Schneider In-Reply-To: <20260225012359.695468795@linuxfoundation.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-DKIM: signer='googlemail.com' status='pass' reason='' DKIMCheck: Server passes DKIM test, 0 Spam score X-Spam-Score: 0.4 (/) X-Spam-Report: Spam detection software, running on the system "witcher.mxrouting.net", has performed the tests listed below against this email. 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See https://www.spamhaus.org/returnc/pub/ [172.232.135.74 listed in zen.spamhaus.org] 1.5 HEADER_FROM_DIFFERENT_DOMAINS From and EnvelopeFrom 2nd level mail domains are different -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature 0.0 URIBL_ZEN_BLOCKED_OPENDNS ADMINISTRATOR NOTICE: The query to zen.spamhaus.org was blocked due to usage of an open resolver. See https://www.spamhaus.org/returnc/pub/ [URIs: peters-netzplatz.de] 0.0 FREEMAIL_FORGED_FROMDOMAIN 2nd level domains in From and EnvelopeFrom freemail headers are different -1.0 MAILING_LIST_MULTI Multiple indicators imply a widely-seen list manager SpamTally: Final spam score: 4 Am 25.02.2026 um 02:11 schrieb Greg Kroah-Hartman: > This is the start of the stable review cycle for the 6.19.4 release. > There are 781 patches in this series, all will be posted as a response > to this one. If anyone has any issues with these being applied, please > let me know. Builds, boots and works on my 2-socket Ivy Bridge Xeon E5-2697 v2 server. No dmesg oddities or regressions found. Tested-by: Peter Schneider Beste Grüße, Peter Schneider -- Climb the mountain not to plant your flag, but to embrace the challenge, enjoy the air and behold the view. 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See https://www.spamhaus.org/returnc/pub/ [URIs: harvard.edu] -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature -1.0 MAILING_LIST_MULTI Multiple indicators imply a widely-seen list manager SpamTally: Final spam score: 4 On Wed, Feb 25, 2026 at 10:31:54AM +0800, Jimmy Hu (xWF) wrote: > On Tue, Feb 24, 2026 at 11:47 PM Alan Stern wrote: > > > > On Tue, Feb 24, 2026 at 04:39:55PM +0800, Jimmy Hu wrote: > > > Commit b81ac4395bbe ("usb: gadget: uvc: allow for application to cleanly > > > shutdown") introduced two stages of synchronization waits totaling 1500ms > > > in uvc_function_unbind() to prevent several types of kernel panics. > > > However, this timing-based approach is insufficient during power > > > management (PM) transitions. > > > > > > When the PM subsystem starts freezing user space processes, the > > > wait_event_interruptible_timeout() is aborted early, which allows the > > > unbind thread to proceed and nullify the gadget pointer > > > (cdev->gadget = NULL): > > > > > > [ 814.123447][ T947] configfs-gadget.g1 gadget.0: uvc: uvc_function_unbind() > > > [ 814.178583][ T3173] PM: suspend entry (deep) > > > [ 814.192487][ T3173] Freezing user space processes > > > [ 814.197668][ T947] configfs-gadget.g1 gadget.0: uvc: uvc_function_unbind no clean disconnect, wait for release > > > > > > When the PM subsystem resumes or aborts the suspend and tasks are > > > restarted, the V4L2 release path is executed and attempts to access the > > > already nullified gadget pointer, triggering a kernel panic: > > > > > > [ 814.292597][ C0] PM: pm_system_irq_wakeup: 479 triggered dhdpcie_host_wake > > > [ 814.386727][ T3173] Restarting tasks ... > > > [ 814.403522][ T4558] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000030 > > > [ 814.404021][ T4558] pc : usb_gadget_deactivate+0x14/0xf4 > > > [ 814.404031][ T4558] lr : usb_function_deactivate+0x54/0x94 > > > [ 814.404078][ T4558] Call trace: > > > [ 814.404080][ T4558] usb_gadget_deactivate+0x14/0xf4 > > > [ 814.404083][ T4558] usb_function_deactivate+0x54/0x94 > > > [ 814.404087][ T4558] uvc_function_disconnect+0x1c/0x5c > > > [ 814.404092][ T4558] uvc_v4l2_release+0x44/0xac > > > [ 814.404095][ T4558] v4l2_release+0xcc/0x130 > > > > > > The fix introduces a 'func_unbinding' flag in struct uvc_device to protect > > > critical sections: > > > 1. In uvc_function_disconnect(), it prevents accessing the nullified > > > cdev->gadget pointer. > > > 2. In uvc_v4l2_release(), it ensures uvcg_free_buffers() is skipped > > > if unbind is already in progress, avoiding races with concurrent > > > bind operations or use-after-free on the video queue memory. > > > > Sorry if the answer to this question is obvious to anybody familiar with > > the driver... > > > > The patch adds a flag that can be accessed by two different tasks > > (disconnect and release). Is there any synchronization to prevent these > > tasks from racing and accessing the new flag concurrently? > > > > Alan Stern > > Hi Alan, > > Thanks for pointing that out. You're right, the boolean flag lacks > proper synchronization for concurrent access. > I will submit a V2 patch using atomic bit operations to ensure memory > visibility and atomicity across tasks. The changes will include: > * Replacing 'bool func_unbinding' with 'unsigned long flags' in struct > uvc_device. > * Using clear_bit() in uvc_function_bind() to reset the state. > * Using set_bit() in uvc_function_unbind() to mark the unbinding phase. > * Using test_bit() in uvc_function_disconnect() and uvc_v4l2_disable() > for safe checks. > > Does this approach look reasonable to you? No, because data races are more complicated than just concurrent non-atomic accesses. There's also the issue of ordering. Here's what I mean... You want to change the bind routine to do something like: cdev->gadget = ... set_bit(&uvc->flags, 0); // Driver is bound and unbind to do something like: clear_bit(&uvc->flags, 0); // Driver is unbound cdev->gadget = NULL; You'll also change disconnect and disable like this: if (test_bit(&uvc->flags, 0)) { ... use cdev->gadget ... } The problem is that modern CPUs can execute instructions out of order and can speculate loads. When the CPU runs the bind routine, there's nothing to prevent it from doing the set_bit() before assigning cdev->gadget. Similarly, when the CPU runs the unbind routine, there's nothing to prevent it from setting cdev->gadget to NULL before doing the clear_bit(). More subtly, when the CPU runs the disconnect or disable routines, there's nothing to prevent it from speculatively reading cdev->gadget (and getting a NULL result) before doing the test_bit() (and getting 1). To prevent these problems, you would need to use memory barriers. For example, you could put smb_wmb() between the two statements in bind and unbind, and smp_rmb() in disconnect and disable before cdev->gadget gets used. (For a lot more information about these memory barriers and other ordering issues, see tools/memory-model/Documentation/explanation.txt.) A simpler approach, if it won't cause any problems, is to ensure synchronization by protecting all these different pieces of code with a mutex. Then they would never execute concurrently. Alan Stern From - Wed Feb 25 16:03:30 2026 X-Mozilla-Status: 0001 X-Mozilla-Status2: 00000000 Return-Path: Delivered-To: hi@josie.lol Received: from witcher.mxrouting.net by witcher.mxrouting.net with LMTP id yNGlKU0dn2k0hxEAYBR5ng (envelope-from ) for ; Wed, 25 Feb 2026 16:03:25 +0000 Return-path: Envelope-to: hi@josie.lol Delivery-date: Wed, 25 Feb 2026 16:03:25 +0000 Received: from sea.lore.kernel.org ([172.234.253.10]) by witcher.mxrouting.net with esmtps (TLS1.3) tls TLS_AES_256_GCM_SHA384 (Exim 4.98) (envelope-from ) id 1vvHMB-00000004uUR-0Xdg for hi@josie.lol; Wed, 25 Feb 2026 16:03:25 +0000 Received: from smtp.subspace.kernel.org (conduit.subspace.kernel.org [100.90.174.1]) by sea.lore.kernel.org (Postfix) with ESMTP id 688D831C2172 for ; Wed, 25 Feb 2026 15:52:50 +0000 (UTC) Received: from localhost.localdomain (localhost.localdomain [127.0.0.1]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 606473D6661; Wed, 25 Feb 2026 15:52:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="zHAGfpMt" X-Original-To: stable@vger.kernel.org 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 1C04D3D330A; Wed, 25 Feb 2026 15:52:00 +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=1772034721; cv=none; b=FXOvEB9FEBDlhtIe2INWDyABK5Wctphls+xZoyOe6l0qHjWw0LAhYIJFN+Sn/khqbA96+aBrWu560HYmyL660Xgqy3etz/FrKpQ0KRt1pKb7XJ1QuSTX9Uuub8o3deZMPdUUBapDjo6GnNK27zCg0drZYg10HiCT2jxN7KKKbOU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772034721; c=relaxed/simple; bh=1rdQ82+haPKF5dBdYw3pwl0TISsvnjieMrrWIGRyRaA=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version:Content-Type; b=pU+TUz4gypQ3fOOZ0H9Q3kojE7x9N7KBh1FHLspJDjhTuTKKEmI/IbM5M/EI/ZJuccamo2jVaAOoF76X/YFknlN5gpe/PoXGLXtLRH+5Xdqe7tiINZJi02vf+XGCQdb76ouOCmaZ5T/EfxEBermdzgNi3jg6dLLI8mIscxxMwFE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=zHAGfpMt; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4A913C116D0; Wed, 25 Feb 2026 15:52:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1772034720; bh=1rdQ82+haPKF5dBdYw3pwl0TISsvnjieMrrWIGRyRaA=; h=From:To:Cc:Subject:Date:From; b=zHAGfpMtfdoqAYfb3hdXTVjJLBKevcakcD3gxc4H5vhXdZ8McppzgP5DR+tBkSP58 YhTuxqmqmS7zOgd/z79vfz2ylB1Ex6ssl3Y6rhqyNfs/Q9+LCUv3iJIsRqyt3uI68d 7ZFcdR0uAbi7X19wGN+QsXFjW83wDckQm9kX+jiA= From: Greg Kroah-Hartman To: stable@vger.kernel.org