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Wed, 20 Aug 2025 13:53:25 -0700 (PDT) Date: Wed, 20 Aug 2025 16:53:22 -0400 From: Alan Stern To: Sebastian Andrzej Siewior Cc: Yunseong Kim , linux-usb@vger.kernel.org, gregkh@linuxfoundation.org, Andrey Konovalov , Shuah Khan , Thomas Gleixner , Clark Williams , Steven Rostedt , linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller@googlegroups.com Subject: Re: [BUG] usbip: vhci: Sleeping function called from invalid context in vhci_urb_enqueue on PREEMPT_RT Message-ID: References: <28544110-3021-43da-b32e-9785c81a42c1@kzalloc.com> <1088432b-b433-4bab-a927-69e55d9eb433@rowland.harvard.edu> <2bf33071-e05e-4b89-b149-30b90888606f@rowland.harvard.edu> <20250819110457.I46wiKTe@linutronix.de> <49ee1b8a-d47a-42df-aa64-d0d62798c45b@rowland.harvard.edu> <20250819145700.sIWRW7Oe@linutronix.de> <20250820162621.UiUQUcp1@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250820162621.UiUQUcp1@linutronix.de> On Wed, Aug 20, 2025 at 06:26:21PM +0200, Sebastian Andrzej Siewior wrote: > The problem is usually that nobody knows why exactly interrupts are > disabled an what purpose it serves. Often the reasons is no longer there > but the code still does it. Indeed, that seems to be the problem in several places here. > > More to the point, out of all the possible reasons why $SOMETHING might > > be invoked with disabled interrupts, which of these reasons remain valid > > in RT builds and which don't? > > None (in most cases) because interrupt handler are threaded. So > interrupts are never truly disabled. > Adding the macros as you suggest would gain probably three users: > - inode > - dummy_hcd > - vhci-hcd > > Instead I would: > - vhci I would suggest to remove the disabling and move its completion > to BH. Agreed. But it's up to the maintainer. > - dummy_hcd I would suggest to either do the thing you called silly or > audit the gadgets and remove it. Auditing is the best approach. It would be a lot of work, though. Also, it's worth noting that other UDC drivers do use the spin_lock_irqsave(); ... spin_unlock(); usb_gadget_giveback_request(); spin_lock(); ... spin_unlock_irqrestore(); scheme, so using it in dummy_hcd would be reasonable. > - inode I would suggest to keep it as-is and audit it properly later > once someone intends to use it. It would also give the opportunity to > clean up the commented locking statement. I don't know if anyone is using AIO with gadgetfs any more. I've never seen any applications for it other than to test the implementation. Alan Stern