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Tue, 10 Mar 2026 07:43:27 +0000 From: "Ionut Nechita (Wind River)" To: linux-pci@vger.kernel.org, bhelgaas@google.com Cc: helgaas@kernel.org, sebott@linux.ibm.com, schnelle@linux.ibm.com, bblock@linux.ibm.com, alifm@linux.ibm.com, julianr@linux.ibm.com, dtatulea@nvidia.com, mani@kernel.org, lukas@wunner.de, kbusch@kernel.org, ionut_n2001@yahoo.com, sunlightlinux@gmail.com, linux-kernel@vger.kernel.org, stable@vger.kernel.org, intel-xe@lists.freedesktop.org, matthew.brost@intel.com, michal.wajdeczko@intel.com, piotr.piorkowski@intel.com, Ionut Nechita Subject: [PATCH v9 1/1] PCI/IOV: Make pci_lock_rescan_remove() reentrant and protect sriov_add_vfs/sriov_del_vfs Date: Tue, 10 Mar 2026 09:43:03 +0200 Message-ID: <20260310074303.17480-2-ionut.nechita@windriver.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260310074303.17480-1-ionut.nechita@windriver.com> References: <20260310074303.17480-1-ionut.nechita@windriver.com> Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: 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adultscore=0 clxscore=1015 bulkscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2602130000 definitions=main-2603100064 Content-Type: text/plain; charset="utf-8" From: Ionut Nechita After reverting commit 05703271c3cd ("PCI/IOV: Add PCI rescan-remove locking when enabling/disabling SR-IOV") and moving the lock to sriov_numvfs_store(), the path through driver .remove() (e.g. rmmod, or manual unbind) that calls pci_disable_sriov() directly remains unprotected against concurrent hotplug events. This affects any SR-IOV capable driver that calls pci_disable_sriov() from its .remove() callback (i40e, ice, mlx5, bnxt, etc.). On s390, platform-generated hot-unplug events for VFs can race with sriov_del_vfs() when a PF driver is being unloaded. The platform event handler takes pci_rescan_remove_lock, but sriov_del_vfs() does not, leading to double removal and list corruption. We cannot use a plain mutex_lock() here because sriov_del_vfs() may also be called from paths that already hold pci_rescan_remove_lock (e.g. remove_store -> pci_stop_and_remove_bus_device_locked, or sriov_numvfs_store with the lock taken by the previous patch). Using mutex_lock() in those cases would deadlock. Make pci_lock_rescan_remove() itself reentrant using mutex_get_owner() and a reentrant depth counter, as suggested by Lukas Wunner and Benjamin Block, since these recursive locking scenarios exist elsewhere in the PCI subsystem: - If the lock is already held by the current task (checked via mutex_get_owner()): increments the reentrant counter and returns without re-acquiring, avoiding deadlock. - If the lock is held by another task: blocks until the lock is released, providing complete serialization. - If the lock is not held: acquires the mutex normally. pci_unlock_rescan_remove() decrements the reentrant counter if it is non-zero, otherwise releases the mutex. This approach keeps the API unchanged: callers simply pair lock/unlock calls without needing to track any return value or use separate reentrant variants. Add pci_lock_rescan_remove()/pci_unlock_rescan_remove() calls to sriov_add_vfs() and sriov_del_vfs() to protect VF addition and removal against concurrent hotplug events. Remove the rescan/remove locking from sriov_numvfs_store() that was introduced by commit a5338e365c45 ("PCI/IOV: Fix race between SR-IOV enable/disable and hotplug"), since the locking is now handled directly in sriov_add_vfs() and sriov_del_vfs() where it is actually needed, reducing the lock scope. Fixes: 18f9e9d150fc ("PCI/IOV: Factor out sriov_add_vfs()") Fixes: 05703271c3cd ("PCI/IOV: Add PCI rescan-remove locking when enabling/= disabling SR-IOV") Fixes: a5338e365c45 ("PCI/IOV: Fix race between SR-IOV enable/disable and h= otplug") Cc: stable@vger.kernel.org Suggested-by: Lukas Wunner Suggested-by: Benjamin Block Reviewed-by: Benjamin Block Tested-by: Benjamin Block Reviewed-by: Niklas Schnelle Tested-by: Niklas Schnelle # s390 Signed-off-by: Ionut Nechita Signed-off-by: Ionut Nechita --- drivers/pci/iov.c | 9 +++++---- drivers/pci/probe.c | 11 +++++++++-- 2 files changed, 14 insertions(+), 6 deletions(-) diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c index 91ac4e37ecb9c..7ed902539051e 100644 --- a/drivers/pci/iov.c +++ b/drivers/pci/iov.c @@ -495,9 +495,7 @@ static ssize_t sriov_numvfs_store(struct device *dev, =20 if (num_vfs =3D=3D 0) { /* disable VFs */ - pci_lock_rescan_remove(); ret =3D pdev->driver->sriov_configure(pdev, 0); - pci_unlock_rescan_remove(); goto exit; } =20 @@ -509,9 +507,7 @@ static ssize_t sriov_numvfs_store(struct device *dev, goto exit; } =20 - pci_lock_rescan_remove(); ret =3D pdev->driver->sriov_configure(pdev, num_vfs); - pci_unlock_rescan_remove(); if (ret < 0) goto exit; =20 @@ -633,15 +629,18 @@ static int sriov_add_vfs(struct pci_dev *dev, u16 num= _vfs) if (dev->no_vf_scan) return 0; =20 + pci_lock_rescan_remove(); for (i =3D 0; i < num_vfs; i++) { rc =3D pci_iov_add_virtfn(dev, i); if (rc) goto failed; } + pci_unlock_rescan_remove(); return 0; failed: while (i--) pci_iov_remove_virtfn(dev, i); + pci_unlock_rescan_remove(); =20 return rc; } @@ -766,8 +765,10 @@ static void sriov_del_vfs(struct pci_dev *dev) struct pci_sriov *iov =3D dev->sriov; int i; =20 + pci_lock_rescan_remove(); for (i =3D 0; i < iov->num_VFs; i++) pci_iov_remove_virtfn(dev, i); + pci_unlock_rescan_remove(); } =20 static void sriov_disable(struct pci_dev *dev) diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c index bccc7a4bdd794..ce4d351b5aa21 100644 --- a/drivers/pci/probe.c +++ b/drivers/pci/probe.c @@ -3509,16 +3509,23 @@ EXPORT_SYMBOL_GPL(pci_rescan_bus); * routines should always be executed under this mutex. */ DEFINE_MUTEX(pci_rescan_remove_lock); +static size_t pci_rescan_remove_reentrant_count; =20 void pci_lock_rescan_remove(void) { - mutex_lock(&pci_rescan_remove_lock); + if (mutex_get_owner(&pci_rescan_remove_lock) =3D=3D (unsigned long)curren= t) + pci_rescan_remove_reentrant_count++; + else + mutex_lock(&pci_rescan_remove_lock); } EXPORT_SYMBOL_GPL(pci_lock_rescan_remove); =20 void pci_unlock_rescan_remove(void) { - mutex_unlock(&pci_rescan_remove_lock); + if (pci_rescan_remove_reentrant_count > 0) + pci_rescan_remove_reentrant_count--; + else + mutex_unlock(&pci_rescan_remove_lock); } EXPORT_SYMBOL_GPL(pci_unlock_rescan_remove); =20 --=20 2.53.0