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Sat, 29 Aug 2026 20:14:11 -0700 (PDT) From: Pierre-David Belanger To: Shixiong Ou Cc: Pierre-David Belanger , Shixiong Ou , Mathias Nyman , Greg Kroah-Hartman , Niklas Neronin , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, regressions@lists.linux.dev Subject: Re: [PATCH] usb: xhci: fix maximum event ring segments calculation Date: Sat, 29 Aug 2026 23:12:32 -0400 Message-ID: <20260830031233.1810986-2-pierredavidbelanger@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260828105926.930033-1-oushixiong1025@163.com> References: <20260828105926.930033-1-oushixiong1025@163.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit I ran into this independently on x86_64 under QEMU and had a regression report half written when I found your patch. Same one line, same reasoning. Confirmed against vanilla mainline 08dbfad3f504, with v7.2 built from the same config for comparison: v7.2 (8d3ae59288f1) USB keyboard enumerates 08dbfad3f504 xhci_hcd does not probe 08dbfad3f504 + this patch USB keyboard enumerates again The failure on 08dbfad3f504: xhci_hcd 0000:00:04.0: xHCI Host Controller xhci_hcd 0000:00:04.0: new USB bus registered, assigned bus number 1 xhci_hcd 0000:00:04.0: Failed to allocate interrupter erst xhci_hcd 0000:00:04.0: can't setup: -12 xhci_hcd 0000:00:04.0: USB bus 1 deregistered xhci_hcd 0000:00:04.0: init 0000:00:04.0 fail, -12 xhci_hcd 0000:00:04.0: probe with driver xhci_hcd failed with error -12 Reproduced with: qemu-system-x86_64 -enable-kvm -m 512 -display none -serial stdio \ -kernel bzImage -initrd initrd \ -device qemu-xhci -device usb-kbd Both -device qemu-xhci and -device nec-usb-xhci are affected. Reading HCSPARAMS2 from inside the guest gives 0x0000000f, so ERST Max really is 0 and max_segs comes out as 0 with the current code. I did not see the page allocator WARNING you hit (my .config is a minimal tinyconfig-derived one), but the probe failure and the -12 are identical, and this patch fixes it. Tested-by: Pierre-David Belanger Thanks for the quick fix. Pierre-David