On Tue, May 7, 2013 at 3:07 AM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> On Mon, 6 May 2013 16:50:07 -0700
> Colin Cross <ccross@xxxxxxxxxxx> wrote:
>
>> CIFS calls wait_event_freezekillable_unsafe with a VFS lock held,
>> which is unsafe and will cause lockdep warnings when 6aa9707
>> "lockdep: check that no locks held at freeze time" is reapplied
>> (it was reverted in dbf520a). CIFS shouldn't be doing this, but
>> it has long-running syscalls that must hold a lock but also
>> shouldn't block suspend. Until CIFS freeze handling is rewritten
>> to use a signal to exit out of the critical section, add a new
>> wait_event_freezekillable_unsafe helper that will not run the
>> lockdep test when 6aa9707 is reapplied, and call it from CIFS.
>>
>> In practice the likley result of holding the lock while freezing
>> is that a second task blocked on the lock will never freeze,
>> aborting suspend, but it is possible to manufacture a case using
>> the cgroup freezer, the lock, and the suspend freezer to create
>> a deadlock. Silencing the lockdep warning here will allow
>> problems to be found in other drivers that may have a more
>> serious deadlock risk, and prevent new problems from being added.
>>
>> Signed-off-by: Colin Cross <ccross@xxxxxxxxxxx>
>> ---
>> include/linux/freezer.h | 13 +++++++++++++
>> 1 file changed, 13 insertions(+)
>>
>> diff --git a/include/linux/freezer.h b/include/linux/freezer.h
>> index 5b31e21c..d3c038e 100644
>> --- a/include/linux/freezer.h
>> +++ b/include/linux/freezer.h
>> @@ -212,6 +212,16 @@ static inline bool freezer_should_skip(struct task_struct *p)
>> __retval; \
>> })
>>
>> +/* DO NOT ADD ANY NEW CALLERS OF THIS FUNCTION */
>> +#define wait_event_freezekillable_unsafe(wq, condition) \
>> +({ \
>> + int __retval; \
>> + freezer_do_not_count(); \
>> + __retval = wait_event_killable(wq, (condition)); \
>> + freezer_count_unsafe(); \
>> + __retval; \
>> +})
>> +
>> #define wait_event_freezable(wq, condition) \
>> ({ \
>> int __retval; \
>> @@ -277,6 +287,9 @@ static inline void set_freezable(void) {}
>> #define wait_event_freezekillable(wq, condition) \
>> wait_event_killable(wq, condition)
>>
>> +#define wait_event_freezekillable_unsafe(wq, condition) \
>> + wait_event_killable(wq, condition)
>> +
>> #endif /* !CONFIG_FREEZER */
>>
>> #endif /* FREEZER_H_INCLUDED */
>
> I think you also need to convert wait_for_response in the cifs code to
> use this helper. While it's a pretty straightforward change, you should
> probably cc linux-cifs@xxxxxxxxxxxxxxx as well.
>
> --
> Jeff Layton <jlayton@xxxxxxxxxx>
Oops, dropped a hunk which is why linux-cifs didn't get cc'd. I will resend it.
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