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[195.135.220.15]) by mx.google.com with ESMTPS id d21si4025849edb.358.2019.05.21.03.46.40 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 21 May 2019 03:46:40 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 4AB4BAF1C; Tue, 21 May 2019 10:46:39 +0000 (UTC) Date: Tue, 21 May 2019 12:46:38 +0200 From: Michal Hocko To: Daniel Vetter Cc: DRI Development , Intel Graphics Development , LKML , Linux MM , Peter Zijlstra , Ingo Molnar , Andrew Morton , David Rientjes , Christian =?iso-8859-1?Q?K=F6nig?= , =?iso-8859-1?B?Suly9G1l?= Glisse , Masahiro Yamada , Wei Wang , Andy Shevchenko , Thomas Gleixner , Jann Horn , Feng Tang , Kees Cook , Randy Dunlap , Daniel Vetter Subject: Re: [PATCH] kernel.h: Add non_block_start/end() Message-ID: <20190521104638.GO32329@dhcp22.suse.cz> References: <20190521100611.10089-1-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: <20190521100611.10089-1-daniel.vetter@ffwll.ch> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue 21-05-19 12:06:11, 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. Quoting Michal: > > "The notifier is called from quite a restricted context - oom_reaper - > which shouldn't depend on any locks or sleepable conditionals. The code > should be swift as well but we mostly do care about it to make a forward > progress. Checking for sleepable context is the best thing we could come > up with that would describe these demands at least partially." > > Peter also asked whether we want to catch spinlocks on top, but Michal > said those are less of a problem because spinlocks can't have an > indirect dependency upon the page allocator and hence close the loop > with the oom reaper. > > Suggested by Michal Hocko. > > v2: > - Improve commit message (Michal) > - Also check in schedule, not just might_sleep (Peter) > > v3: It works better when I actually squash in the fixup I had lying > around :-/ > > Cc: Peter Zijlstra > Cc: Ingo Molnar > Cc: Andrew Morton > Cc: Michal Hocko > Cc: David Rientjes > Cc: "Christian König" > Cc: Daniel Vetter > Cc: "Jérôme Glisse" > Cc: linux-mm@kvack.org > Cc: Masahiro Yamada > Cc: Wei Wang > Cc: Andy Shevchenko > Cc: Thomas Gleixner > Cc: Jann Horn > Cc: Feng Tang > Cc: Kees Cook > Cc: Randy Dunlap > Cc: linux-kernel@vger.kernel.org > Acked-by: Christian König (v1) > Signed-off-by: Daniel Vetter I like this in general. The implementation looks reasonable to me but I didn't check deeply enough to give my R-by or A-by. > --- > include/linux/kernel.h | 10 +++++++++- > include/linux/sched.h | 4 ++++ > kernel/sched/core.c | 19 ++++++++++++++----- > 3 files changed, 27 insertions(+), 6 deletions(-) > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h > index 74b1ee9027f5..b5f2c2ff0eab 100644 > --- a/include/linux/kernel.h > +++ b/include/linux/kernel.h > @@ -214,7 +214,9 @@ extern void __cant_sleep(const char *file, int line, int preempt_offset); > * 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 > @@ -230,6 +232,10 @@ extern void __cant_sleep(const char *file, int line, int preempt_offset); > # define cant_sleep() \ > do { __cant_sleep(__FILE__, __LINE__, 0); } 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) { } > @@ -238,6 +244,8 @@ extern void __cant_sleep(const char *file, int line, int preempt_offset); > # define might_sleep() do { might_resched(); } while (0) > # define cant_sleep() do { } 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 11837410690f..7f5b293e72df 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -908,6 +908,10 @@ 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 102dfcf0a29a..ed7755a28465 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3264,13 +3264,22 @@ static noinline void __schedule_bug(struct task_struct *prev) > /* > * Various schedule()-time debugging checks and statistics: > */ > -static inline void schedule_debug(struct task_struct *prev) > +static inline void schedule_debug(struct task_struct *prev, bool preempt) > { > #ifdef CONFIG_SCHED_STACK_END_CHECK > if (task_stack_end_corrupted(prev)) > panic("corrupted stack end detected inside scheduler\n"); > #endif > > +#ifdef CONFIG_DEBUG_ATOMIC_SLEEP > + if (!preempt && prev->state && prev->non_block_count) { > + printk(KERN_ERR "BUG: scheduling in a non-blocking section: %s/%d/%i\n", > + prev->comm, prev->pid, prev->non_block_count); > + dump_stack(); > + add_taint(TAINT_WARN, LOCKDEP_STILL_OK); > + } > +#endif > + > if (unlikely(in_atomic_preempt_off())) { > __schedule_bug(prev); > preempt_count_set(PREEMPT_DISABLED); > @@ -3377,7 +3386,7 @@ static void __sched notrace __schedule(bool preempt) > rq = cpu_rq(cpu); > prev = rq->curr; > > - schedule_debug(prev); > + schedule_debug(prev, preempt); > > if (sched_feat(HRTICK)) > hrtick_clear(rq); > @@ -6102,7 +6111,7 @@ 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; > @@ -6118,8 +6127,8 @@ 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)) > -- > 2.20.1 > -- Michal Hocko SUSE Labs