From mboxrd@z Thu Jan 1 00:00:00 1970 From: Colin Cross Subject: Re: [PATCH v3 02/16] freezer: add unsafe versions of freezable helpers for CIFS Date: Tue, 7 May 2013 10:47:36 -0700 Message-ID: References: <1367884221-20462-1-git-send-email-ccross@android.com> <1367884221-20462-3-git-send-email-ccross@android.com> <20130507060730.03364687@tlielax.poochiereds.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: lkml , Pavel Machek , "Rafael J. Wysocki" , Peter Zijlstra , Ingo Molnar , Andrew Morton , Mandeep Singh Baines , Oleg Nesterov , linux-nfs , Linux PM list , netdev , Linus Torvalds , Tejun Heo , Len Brown To: Jeff Layton Return-path: In-Reply-To: <20130507060730.03364687-9yPaYZwiELC+kQycOl6kW4xkIHaj4LzF@public.gmane.org> Sender: linux-nfs-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: netdev.vger.kernel.org On Tue, May 7, 2013 at 3:07 AM, Jeff Layton wrote: > On Mon, 6 May 2013 16:50:07 -0700 > Colin Cross 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 >> --- >> 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-u79uwXL29TY76Z2rM5mHXA@public.gmane.org as well. > > -- > Jeff Layton Oops, dropped a hunk which is why linux-cifs didn't get cc'd. I will resend it. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html