[PATCH 5.10 04/19] ACPI: NFIT: fix a potential deadlock during NFIT teardown

Greg Kroah-Hartman
2023-03-01T18:09:45Z

From: Vishal Verma <vishal.l.verma@intel.com>

[ 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@intel.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Link: https://lore.kernel.org/r/20230112-acpi_nfit_lockdep-v1-1-660be4dd10be@intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/acpi/nfit/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
index 99e23a5df0267..2306abb09f7f5 100644
--- a/drivers/acpi/nfit/core.c
+++ b/drivers/acpi/nfit/core.c
@@ -3687,8 +3687,8 @@ 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
--
2.39.0