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    Subject[PATCH AUTOSEL 5.15 06/12] ACPI: NFIT: fix a potential deadlock during NFIT teardown
    Date
    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 7dd80acf92c78..2575d6c51f898 100644
    --- a/drivers/acpi/nfit/core.c
    +++ b/drivers/acpi/nfit/core.c
    @@ -3676,8 +3676,8 @@ 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
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