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    SubjectRe: [PATCH -v2] acpi: Fix possible recursive locking in hwregs.c
    On 11/06/2011 08:48 PM, Rakib Mullick wrote:
    > Calling pm-suspend might trigger a recursive lock in it's code path. In function acpi_hw_clear_acpi_status, acpi_os_acquire_lock holds the lock acpi_gbl_hardware_lock before calling acpi_hw_register_write(), then without releasing acpi_gbl_hardware_lock, this function calls acpi_ev_walk_gpe_list, which tries to hold acpi_gbl_gpe_lock. Both acpi_gbl_hardware_lock and acpi_gbl_gpe_lock are at same lock-class and which might cause lock recursion deadlock.
    >
    > Following patch fixes this scenario by just releasing acpi_gbl_hardware_lock before calling acpi_ev_walk_gpe_list.
    >
    > Changes since v0(https://lkml.org/lkml/2011/9/21/355):
    > - Fix changelog, thanks to Lin Ming.
    >
    > Changes since v1 (https://lkml.org/lkml/2011/11/3/89):
    > - Update changelog and rename goto label, courtesy Srivatsa S. Bhat.
    >
    > Signed-off-by: Rakib Mullick <rakib.mullick@gmail.com>
    > Cc: Lin Ming <ming.m.lin@intel.com>
    > Cc: Andrew Morton <akpm@linux-foundation.org>
    > Cc: Len Brown <len.brown@intel.com>
    > Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    > ---
    >

    It would be a good idea to also give the lockdep warning in the changelog
    (though you triggered it in a modified kernel), since that would make
    it very clear as to what problem your patch is trying to solve.
    [And please line-wrap your changelog to 80 characters at most, per line].

    Code-wise, the patch looks good to me. So,
    Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>

    Thanks,
    Srivatsa S. Bhat

    > diff --git a/drivers/acpi/acpica/hwregs.c b/drivers/acpi/acpica/hwregs.c
    > index 55accb7..cc70f3f 100644
    > --- a/drivers/acpi/acpica/hwregs.c
    > +++ b/drivers/acpi/acpica/hwregs.c
    > @@ -269,16 +269,17 @@ acpi_status acpi_hw_clear_acpi_status(void)
    >
    > status = acpi_hw_register_write(ACPI_REGISTER_PM1_STATUS,
    > ACPI_BITMASK_ALL_FIXED_STATUS);
    > - if (ACPI_FAILURE(status)) {
    > - goto unlock_and_exit;
    > - }
    > +
    > + acpi_os_release_lock(acpi_gbl_hardware_lock, lock_flags);
    > +
    > + if (ACPI_FAILURE(status))
    > + goto exit;
    >
    > /* Clear the GPE Bits in all GPE registers in all GPE blocks */
    >
    > status = acpi_ev_walk_gpe_list(acpi_hw_clear_gpe_block, NULL);
    >
    > - unlock_and_exit:
    > - acpi_os_release_lock(acpi_gbl_hardware_lock, lock_flags);
    > +exit:
    > return_ACPI_STATUS(status);
    > }
    >
    >
    >


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