This is a note to let you know that I've just added the patch titled ACPI: NFIT: fix a potential deadlock during NFIT teardown to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: acpi-nfit-fix-a-potential-deadlock-during-nfit-teard.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 19b48781fb117670ada334c5b6851b7170b1cf17 Author: Vishal Verma <vishal.l.verma@xxxxxxxxx> Date: Wed Jan 25 11:34:18 2023 -0700 ACPI: NFIT: fix a potential deadlock during NFIT teardown [ Upstream commit fb6df4366f86dd252bfa3049edffa52d17e7b895 ] Lockdep reports that acpi_nfit_shutdown() may deadlock against an opportune acpi_nfit_scrub(). acpi_nfit_scrub () is run from inside a 'work' and therefore has already acquired workqueue-internal locks. It also acquiires acpi_desc->init_mutex. acpi_nfit_shutdown() first acquires init_mutex, and was subsequently attempting to cancel any pending workqueue items. This reversed locking order causes a potential deadlock: ====================================================== WARNING: possible circular locking dependency detected 6.2.0-rc3 #116 Tainted: G O N ------------------------------------------------------ libndctl/1958 is trying to acquire lock: ffff888129b461c0 ((work_completion)(&(&acpi_desc->dwork)->work)){+.+.}-{0:0}, at: __flush_work+0x43/0x450 but task is already holding lock: ffff888129b460e8 (&acpi_desc->init_mutex){+.+.}-{3:3}, at: acpi_nfit_shutdown+0x87/0xd0 [nfit] which lock already depends on the new lock. ... Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&acpi_desc->init_mutex); lock((work_completion)(&(&acpi_desc->dwork)->work)); lock(&acpi_desc->init_mutex); lock((work_completion)(&(&acpi_desc->dwork)->work)); *** DEADLOCK *** Since the workqueue manipulation is protected by its own internal locking, the cancellation of pending work doesn't need to be done under acpi_desc->init_mutex. Move cancel_delayed_work_sync() outside the init_mutex to fix the deadlock. Any work that starts after acpi_nfit_shutdown() drops the lock will see ARS_CANCEL, and the cancel_delayed_work_sync() will safely flush it out. Reported-by: Dan Williams <dan.j.williams@xxxxxxxxx> Signed-off-by: Vishal Verma <vishal.l.verma@xxxxxxxxx> Link: https://lore.kernel.org/r/20230112-acpi_nfit_lockdep-v1-1-660be4dd10be@xxxxxxxxx Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c index 0fe4f3ed72ca4..793b8d9d749a0 100644 --- a/drivers/acpi/nfit/core.c +++ b/drivers/acpi/nfit/core.c @@ -3599,8 +3599,8 @@ void acpi_nfit_shutdown(void *data) mutex_lock(&acpi_desc->init_mutex); set_bit(ARS_CANCEL, &acpi_desc->scrub_flags); - cancel_delayed_work_sync(&acpi_desc->dwork); mutex_unlock(&acpi_desc->init_mutex); + cancel_delayed_work_sync(&acpi_desc->dwork); /* * Bounce the nvdimm bus lock to make sure any in-flight