The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y git checkout FETCH_HEAD git cherry-pick -x 4b1815a52d7eb03b3e0e6742c6728bc16a4b2d1d # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025062009-passover-legibly-3a57@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 4b1815a52d7eb03b3e0e6742c6728bc16a4b2d1d Mon Sep 17 00:00:00 2001 From: Niklas Schnelle schnelle@linux.ibm.com Date: Thu, 22 May 2025 14:13:14 +0200 Subject: [PATCH] s390/pci: Allow re-add of a reserved but not yet removed device

The architecture assumes that PCI functions can be removed synchronously as PCI events are processed. This however clashes with the reference counting of struct pci_dev which allows device drivers to hold on to a struct pci_dev reference even as the underlying device is removed. To bridge this gap commit 2a671f77ee49 ("s390/pci: fix use after free of zpci_dev") keeps the struct zpci_dev in ZPCI_FN_STATE_RESERVED state until common code releases the struct pci_dev. Only when all references are dropped, the struct zpci_dev can be removed and freed.

Later commit a46044a92add ("s390/pci: fix zpci_zdev_put() on reserve") moved the deletion of the struct zpci_dev from the zpci_list in zpci_release_device() to the point where the device is reserved. This was done to prevent handling events for a device that is already being removed, e.g. when the platform generates both PCI event codes 0x304 and 0x308. In retrospect, deletion from the zpci_list in the release function without holding the zpci_list_lock was also racy.

A side effect of this handling is that if the underlying device re-appears while the struct zpci_dev is in the ZPCI_FN_STATE_RESERVED state, the new and old instances of the struct zpci_dev and/or struct pci_dev may clash. For example when trying to create the IOMMU sysfs files for the new instance. In this case, re-adding the new instance is aborted. The old instance is removed, and the device will remain absent until the platform issues another event.

Fix this by allowing the struct zpci_dev to be brought back up right until it is finally removed. To this end also keep the struct zpci_dev in the zpci_list until it is finally released when all references have been dropped.

Deletion from the zpci_list from within the release function is made safe by using kref_put_lock() with the zpci_list_lock. This ensures that the releasing code holds the last reference.

Cc: stable@vger.kernel.org Fixes: a46044a92add ("s390/pci: fix zpci_zdev_put() on reserve") Reviewed-by: Gerd Bayer gbayer@linux.ibm.com Tested-by: Gerd Bayer gbayer@linux.ibm.com Signed-off-by: Niklas Schnelle schnelle@linux.ibm.com Signed-off-by: Heiko Carstens hca@linux.ibm.com

diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c index 9fcc6d3180f2..4602abd0c6f1 100644 --- a/arch/s390/pci/pci.c +++ b/arch/s390/pci/pci.c @@ -70,6 +70,13 @@ EXPORT_SYMBOL_GPL(zpci_aipb); struct airq_iv *zpci_aif_sbv; EXPORT_SYMBOL_GPL(zpci_aif_sbv);

+void zpci_zdev_put(struct zpci_dev *zdev) +{ + if (!zdev) + return; + kref_put_lock(&zdev->kref, zpci_release_device, &zpci_list_lock); +} + struct zpci_dev *get_zdev_by_fid(u32 fid) { struct zpci_dev *tmp, *zdev = NULL; @@ -925,21 +932,20 @@ int zpci_deconfigure_device(struct zpci_dev *zdev) * @zdev: the zpci_dev that was reserved * * Handle the case that a given zPCI function was reserved by another system. - * After a call to this function the zpci_dev can not be found via - * get_zdev_by_fid() anymore but may still be accessible via existing - * references though it will not be functional anymore. */ void zpci_device_reserved(struct zpci_dev *zdev) { - /* - * Remove device from zpci_list as it is going away. This also - * makes sure we ignore subsequent zPCI events for this device. - */ - spin_lock(&zpci_list_lock); - list_del(&zdev->entry); - spin_unlock(&zpci_list_lock); + lockdep_assert_held(&zdev->state_lock); + /* We may declare the device reserved multiple times */ + if (zdev->state == ZPCI_FN_STATE_RESERVED) + return; zdev->state = ZPCI_FN_STATE_RESERVED; zpci_dbg(3, "rsv fid:%x\n", zdev->fid); + /* + * The underlying device is gone. Allow the zdev to be freed + * as soon as all other references are gone by accounting for + * the removal as a dropped reference. + */ zpci_zdev_put(zdev); }

@@ -948,6 +954,12 @@ void zpci_release_device(struct kref *kref) struct zpci_dev *zdev = container_of(kref, struct zpci_dev, kref);

WARN_ON(zdev->state != ZPCI_FN_STATE_RESERVED); + /* + * We already hold zpci_list_lock thanks to kref_put_lock(). + * This makes sure no new reference can be taken from the list. + */ + list_del(&zdev->entry); + spin_unlock(&zpci_list_lock);

if (zdev->has_hp_slot) zpci_exit_slot(zdev); diff --git a/arch/s390/pci/pci_bus.h b/arch/s390/pci/pci_bus.h index e86a9419d233..ae3d7a9159bd 100644 --- a/arch/s390/pci/pci_bus.h +++ b/arch/s390/pci/pci_bus.h @@ -21,11 +21,8 @@ int zpci_bus_scan_device(struct zpci_dev *zdev); void zpci_bus_remove_device(struct zpci_dev *zdev, bool set_error);

void zpci_release_device(struct kref *kref); -static inline void zpci_zdev_put(struct zpci_dev *zdev) -{ - if (zdev) - kref_put(&zdev->kref, zpci_release_device); -} + +void zpci_zdev_put(struct zpci_dev *zdev);

static inline void zpci_zdev_get(struct zpci_dev *zdev) { diff --git a/arch/s390/pci/pci_event.c b/arch/s390/pci/pci_event.c index 7bd7721c1239..2fbee3887d13 100644 --- a/arch/s390/pci/pci_event.c +++ b/arch/s390/pci/pci_event.c @@ -335,6 +335,22 @@ static void zpci_event_hard_deconfigured(struct zpci_dev *zdev, u32 fh) zdev->state = ZPCI_FN_STATE_STANDBY; }

+static void zpci_event_reappear(struct zpci_dev *zdev) +{ + lockdep_assert_held(&zdev->state_lock); + /* + * The zdev is in the reserved state. This means that it was presumed to + * go away but there are still undropped references. Now, the platform + * announced its availability again. Bring back the lingering zdev + * to standby. This is safe because we hold a temporary reference + * now so that it won't go away. Account for the re-appearance of the + * underlying device by incrementing the reference count. + */ + zdev->state = ZPCI_FN_STATE_STANDBY; + zpci_zdev_get(zdev); + zpci_dbg(1, "rea fid:%x, fh:%x\n", zdev->fid, zdev->fh); +} + static void __zpci_event_availability(struct zpci_ccdf_avail *ccdf) { struct zpci_dev *zdev = get_zdev_by_fid(ccdf->fid); @@ -358,8 +374,10 @@ static void __zpci_event_availability(struct zpci_ccdf_avail *ccdf) break; } } else { + if (zdev->state == ZPCI_FN_STATE_RESERVED) + zpci_event_reappear(zdev); /* the configuration request may be stale */ - if (zdev->state != ZPCI_FN_STATE_STANDBY) + else if (zdev->state != ZPCI_FN_STATE_STANDBY) break; zdev->state = ZPCI_FN_STATE_CONFIGURED; } @@ -375,6 +393,8 @@ static void __zpci_event_availability(struct zpci_ccdf_avail *ccdf) break; } } else { + if (zdev->state == ZPCI_FN_STATE_RESERVED) + zpci_event_reappear(zdev); zpci_update_fh(zdev, ccdf->fh); } break;