Fault-injection capability for kmalloc (FAILSLAB) #7

pmenzel · 2025-09-11T07:05:45Z

For those ignorant like me:

Linux has fault injection infrastructure. An Amazon developer actually used it for testing their patch:

#!/bin/bash -ex

FAILSLAB_PATH=/sys/kernel/debug/failslab/
DEVICE=0000:00:05.0
START_ADDR=$(grep " igc_led_setup" /proc/kallsyms \
        | awk '{printf("0x%s", $1)}')
END_ADDR=$(printf "0x%x" $((START_ADDR + 0x100)))

echo $START_ADDR > $FAILSLAB_PATH/require-start
echo $END_ADDR > $FAILSLAB_PATH/require-end
echo 1 > $FAILSLAB_PATH/times
echo 100 > $FAILSLAB_PATH/probability
echo N > $FAILSLAB_PATH/ignore-gfp-wait

echo $DEVICE > /sys/bus/pci/drivers/igc/bind

The MarIuX Linux kernel does not have this infrastructure enabled, but it’s easy to build it yourself.

The text was updated successfully, but these errors were encountered:

When s_start() fails to allocate memory for set_event_iter, it returns NULL before acquiring event_mutex. However, the corresponding s_stop() function always tries to unlock the mutex, causing a lock imbalance warning: WARNING: bad unlock balance detected! 6.17.0-rc7-00175-g2b2e0c04f78c #7 Not tainted ------------------------------------- syz.0.85611/376514 is trying to release lock (event_mutex) at: [<ffffffff8dafc7a4>] traverse.part.0.constprop.0+0x2c4/0x650 fs/seq_file.c:131 but there are no more locks to release! The issue was introduced by commit b355247 ("tracing: Cache ':mod:' events for modules not loaded yet") which added the kzalloc() allocation before the mutex lock, creating a path where s_start() could return without locking the mutex while s_stop() would still try to unlock it. Fix this by unconditionally acquiring the mutex immediately after allocation, regardless of whether the allocation succeeded. Cc: stable@vger.kernel.org Link: https://lore.kernel.org/20250929113238.3722055-1-sashal@kernel.org Fixes: b355247 ("tracing: Cache ":mod:" events for modules not loaded yet") Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Before disabling SR-IOV via config space accesses to the parent PF, sriov_disable() first removes the PCI devices representing the VFs. Since commit 9d16947 ("PCI: Add global pci_lock_rescan_remove()") such removal operations are serialized against concurrent remove and rescan using the pci_rescan_remove_lock. No such locking was ever added in sriov_disable() however. In particular when commit 18f9e9d ("PCI/IOV: Factor out sriov_add_vfs()") factored out the PCI device removal into sriov_del_vfs() there was still no locking around the pci_iov_remove_virtfn() calls. On s390 the lack of serialization in sriov_disable() may cause double remove and list corruption with the below (amended) trace being observed: PSW: 0704c00180000000 0000000c914e4b38 (klist_put+56) GPRS: 000003800313fb48 0000000000000000 0000000100000001 0000000000000001 00000000f9b520a8 0000000000000000 0000000000002fbd 00000000f4cc9480 0000000000000001 0000000000000000 0000000000000000 0000000180692828 00000000818e8000 000003800313fe2c 000003800313fb20 000003800313fad8 #0 [3800313fb20] device_del at c9158ad5c #1 [3800313fb88] pci_remove_bus_device at c915105ba #2 [3800313fbd0] pci_iov_remove_virtfn at c9152f198 #3 [3800313fc28] zpci_iov_remove_virtfn at c90fb67c0 #4 [3800313fc60] zpci_bus_remove_device at c90fb6104 #5 [3800313fca0] __zpci_event_availability at c90fb3dca #6 [3800313fd08] chsc_process_sei_nt0 at c918fe4a2 #7 [3800313fd60] crw_collect_info at c91905822 #8 [3800313fe10] kthread at c90feb390 #9 [3800313fe68] __ret_from_fork at c90f6aa64 #10 [3800313fe98] ret_from_fork at c9194f3f2. This is because in addition to sriov_disable() removing the VFs, the platform also generates hot-unplug events for the VFs. This being the reverse operation to the hotplug events generated by sriov_enable() and handled via pdev->no_vf_scan. And while the event processing takes pci_rescan_remove_lock and checks whether the struct pci_dev still exists, the lack of synchronization makes this checking racy. Other races may also be possible of course though given that this lack of locking persisted so long observable races seem very rare. Even on s390 the list corruption was only observed with certain devices since the platform events are only triggered by config accesses after the removal, so as long as the removal finished synchronously they would not race. Either way the locking is missing so fix this by adding it to the sriov_del_vfs() helper. Just like PCI rescan-remove, locking is also missing in sriov_add_vfs() including for the error case where pci_stop_and_remove_bus_device() is called without the PCI rescan-remove lock being held. Even in the non-error case, adding new PCI devices and buses should be serialized via the PCI rescan-remove lock. Add the necessary locking. Fixes: 18f9e9d ("PCI/IOV: Factor out sriov_add_vfs()") Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Reviewed-by: Benjamin Block <bblock@linux.ibm.com> Reviewed-by: Farhan Ali <alifm@linux.ibm.com> Reviewed-by: Julian Ruess <julianr@linux.ibm.com> Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20250826-pci_fix_sriov_disable-v1-1-2d0bc938f2a3@linux.ibm.com

pmenzel closed this as completed Sep 11, 2025

Fault-injection capability for kmalloc (FAILSLAB) #7

Fault-injection capability for kmalloc (FAILSLAB) #7

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pmenzel commented Sep 11, 2025