From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by kanga.kvack.org (Postfix) with ESMTP id 2CCE98E0018 for ; Mon, 10 Dec 2018 09:13:40 -0500 (EST) Received: by mail-ed1-f69.google.com with SMTP id f17so4228272edm.20 for ; Mon, 10 Dec 2018 06:13:40 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id l1si1048628edn.1.2018.12.10.06.13.38 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 10 Dec 2018 06:13:38 -0800 (PST) Date: Mon, 10 Dec 2018 15:13:37 +0100 From: Michal Hocko Subject: Re: [PATCH 2/4] kernel.h: Add non_block_start/end() Message-ID: <20181210141337.GQ1286@dhcp22.suse.cz> References: <20181210103641.31259-1-daniel.vetter@ffwll.ch> <20181210103641.31259-3-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20181210103641.31259-3-daniel.vetter@ffwll.ch> Sender: owner-linux-mm@kvack.org List-ID: To: Daniel Vetter Cc: Intel Graphics Development , DRI Development , LKML , linux-mm@kvack.org, Andrew Morton , David Rientjes , Christian =?iso-8859-1?Q?K=F6nig?= , =?iso-8859-1?B?Suly9G1l?= Glisse , Daniel Vetter , Peter Zijlstra I do not see any scheduler guys Cced and it would be really great to get their opinion here. On Mon 10-12-18 11:36:39, Daniel Vetter wrote: > In some special cases we must not block, but there's not a > spinlock, preempt-off, irqs-off or similar critical section already > that arms the might_sleep() debug checks. Add a non_block_start/end() > pair to annotate these. > > This will be used in the oom paths of mmu-notifiers, where blocking is > not allowed to make sure there's forward progress. Considering the only alternative would be to abuse preempt_{disable,enable}, and that really has a different semantic, I think this makes some sense. The cotext is preemptible but we do not want notifier to sleep on any locks, WQ etc. > Suggested by Michal Hocko. > > Cc: Andrew Morton > Cc: Michal Hocko > Cc: David Rientjes > Cc: "Christian K�nig" > Cc: Daniel Vetter > Cc: "J�r�me Glisse" > Cc: linux-mm@kvack.org > Signed-off-by: Daniel Vetter > --- > include/linux/kernel.h | 10 +++++++++- > include/linux/sched.h | 4 ++++ > kernel/sched/core.c | 6 +++--- > 3 files changed, 16 insertions(+), 4 deletions(-) > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h > index d6aac75b51ba..c2cf31515b3d 100644 > --- a/include/linux/kernel.h > +++ b/include/linux/kernel.h > @@ -251,7 +251,9 @@ extern int _cond_resched(void); > * might_sleep - annotation for functions that can sleep > * > * this macro will print a stack trace if it is executed in an atomic > - * context (spinlock, irq-handler, ...). > + * context (spinlock, irq-handler, ...). Additional sections where blocking is > + * not allowed can be annotated with non_block_start() and non_block_end() > + * pairs. > * > * This is a useful debugging help to be able to catch problems early and not > * be bitten later when the calling function happens to sleep when it is not > @@ -260,6 +262,10 @@ extern int _cond_resched(void); > # define might_sleep() \ > do { __might_sleep(__FILE__, __LINE__, 0); might_resched(); } while (0) > # define sched_annotate_sleep() (current->task_state_change = 0) > +# define non_block_start() \ > + do { current->non_block_count++; } while (0) > +# define non_block_end() \ > + do { WARN_ON(current->non_block_count-- == 0); } while (0) > #else > static inline void ___might_sleep(const char *file, int line, > int preempt_offset) { } > @@ -267,6 +273,8 @@ extern int _cond_resched(void); > int preempt_offset) { } > # define might_sleep() do { might_resched(); } while (0) > # define sched_annotate_sleep() do { } while (0) > +# define non_block_start() do { } while (0) > +# define non_block_end() do { } while (0) > #endif > > #define might_sleep_if(cond) do { if (cond) might_sleep(); } while (0) > diff --git a/include/linux/sched.h b/include/linux/sched.h > index ecffd4e37453..41249dbf8f27 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -916,6 +916,10 @@ struct task_struct { > struct mutex_waiter *blocked_on; > #endif > > +#ifdef CONFIG_DEBUG_ATOMIC_SLEEP > + int non_block_count; > +#endif > + > #ifdef CONFIG_TRACE_IRQFLAGS > unsigned int irq_events; > unsigned long hardirq_enable_ip; > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 6fedf3a98581..969d7a71f30c 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -6113,7 +6113,7 @@ void ___might_sleep(const char *file, int line, int preempt_offset) > rcu_sleep_check(); > > if ((preempt_count_equals(preempt_offset) && !irqs_disabled() && > - !is_idle_task(current)) || > + !is_idle_task(current) && !current->non_block_count) || > system_state == SYSTEM_BOOTING || system_state > SYSTEM_RUNNING || > oops_in_progress) > return; > @@ -6129,8 +6129,8 @@ void ___might_sleep(const char *file, int line, int preempt_offset) > "BUG: sleeping function called from invalid context at %s:%d\n", > file, line); > printk(KERN_ERR > - "in_atomic(): %d, irqs_disabled(): %d, pid: %d, name: %s\n", > - in_atomic(), irqs_disabled(), > + "in_atomic(): %d, irqs_disabled(): %d, non_block: %d, pid: %d, name: %s\n", > + in_atomic(), irqs_disabled(), current->non_block_count, > current->pid, current->comm); > > if (task_stack_end_corrupted(current)) > -- > 2.20.0.rc1 > -- Michal Hocko SUSE Labs