From: Julien Thierry <julien.thierry@arm.com>
To: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>
Cc: catalin.marinas@arm.com, will.deacon@arm.com,
linux-kernel@vger.kernel.org, mingo@redhat.com,
james.morse@arm.com, hpa@zytor.com, valentin.schneider@arm.com,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 3/4] uaccess: Check no rescheduling function is called in unsafe region
Date: Tue, 12 Feb 2019 09:15:13 +0000 [thread overview]
Message-ID: <a23fdd84-8c4b-0c1f-d877-24d946cff6d0@arm.com> (raw)
In-Reply-To: <20190211135159.GC32511@hirez.programming.kicks-ass.net>
On 11/02/2019 13:51, Peter Zijlstra wrote:
> On Mon, Feb 11, 2019 at 02:45:27PM +0100, Ingo Molnar wrote:
>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>>> index a674c7db..b1bb7e9 100644
>>> --- a/kernel/sched/core.c
>>> +++ b/kernel/sched/core.c
>>> @@ -3289,6 +3289,14 @@ static inline void schedule_debug(struct task_struct *prev)
>>> __schedule_bug(prev);
>>> preempt_count_set(PREEMPT_DISABLED);
>>> }
>>> +
>>> + if (IS_ENABLED(CONFIG_DEBUG_UACCESS_SLEEP) &&
>>> + unlikely(unsafe_user_region_active())) {
>>> + printk(KERN_ERR "BUG: scheduling while user_access enabled: %s/%d/0x%08x\n",
>>> + prev->comm, prev->pid, preempt_count());
>>> + dump_stack();
>>> + }
>>> +
>>> rcu_sleep_check();
>>>
>>> profile_hit(SCHED_PROFILING, __builtin_return_address(0));
>>> @@ -6151,6 +6159,20 @@ void ___might_sleep(const char *file, int line, int preempt_offset)
>>> EXPORT_SYMBOL(___might_sleep);
>>> #endif
>>>
>>> +#ifdef CONFIG_DEBUG_UACCESS_SLEEP
>>> +void __might_resched(const char *file, int line)
>>> +{
>>> + if (!unsafe_user_region_active())
>>> + return;
>>
>> Could you please more clearly explain why you want/need an exception from
>> the __might_resched() debug warning?
So, the scenarios I'm trying to avoid are of the following flavour:
if (user_access_begin(ptr, size)) {
[...]
// Calling a function that might call schedule()
[...]
user_access_end();
}
The thing is, as I understand, not all function that call schedule() are
annotated with might_resched(), and on the other hand, not every time we
call a function that might_resched() will it call schedule().
Now with Peter's remark I think I might have been overzealous.
>
> In specific; how is the addition in schedule_debug() not triggering on
> PREEMPT=y kernels?
>
> If code is preemptible, you can (get) schedule(d). If it is not
> preemptible; you do not need these additional tests.
>
Yes that sounds right, might_resched() only potentially reschedules if
in a suitable context, so best case I issue two warnings, worst case I
actually be warn when the caller took care to disable preemption or
interrupts before calling a might_resched().
I guess I got a bit confused with might_sleep() which is "if you call
this in the wrong context I warn" whereas might_resched() is just "if
you call this in preemptible context, lets resched".
I guess I'll drop the might_resched() part of this patch if that sounds
alright.
Thanks,
--
Julien Thierry
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next prev parent reply other threads:[~2019-02-12 9:15 UTC|newest]
Thread overview: 88+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-15 13:58 [PATCH v3 0/4] uaccess: Add unsafe accessors for arm64 Julien Thierry
2019-01-15 13:58 ` [PATCH v3 1/4] arm64: uaccess: Cleanup get/put_user() Julien Thierry
2019-01-15 13:58 ` [PATCH v3 2/4] arm64: uaccess: Implement unsafe accessors Julien Thierry
2019-01-15 13:58 ` [PATCH v3 3/4] uaccess: Check no rescheduling function is called in unsafe region Julien Thierry
2019-01-30 16:58 ` Valentin Schneider
2019-02-04 13:27 ` Julien Thierry
2019-02-11 13:45 ` Ingo Molnar
2019-02-11 13:51 ` Peter Zijlstra
2019-02-12 9:15 ` Julien Thierry [this message]
2019-02-13 8:21 ` Ingo Molnar
2019-02-13 10:35 ` Peter Zijlstra
2019-02-13 10:50 ` Julien Thierry
2019-02-13 13:17 ` Peter Zijlstra
2019-02-13 13:20 ` Peter Zijlstra
2019-02-13 14:00 ` Will Deacon
2019-02-13 14:07 ` Julien Thierry
2019-02-13 14:17 ` Peter Zijlstra
2019-02-13 14:24 ` Julien Thierry
2019-02-13 14:40 ` Peter Zijlstra
2019-02-13 15:08 ` Peter Zijlstra
2019-02-13 14:25 ` Peter Zijlstra
2019-02-13 14:39 ` Julien Thierry
2019-02-13 14:41 ` Peter Zijlstra
2019-02-13 15:45 ` Peter Zijlstra
2019-02-13 18:54 ` Peter Zijlstra
[not found] ` <D61C430D-4321-4114-AB85-671A3C7B8EAE@amacapital.net>
2019-02-13 22:21 ` Peter Zijlstra
2019-02-13 22:49 ` Andy Lutomirski
2019-02-14 10:14 ` [PATCH] sched/x86: Save [ER]FLAGS on context switch Peter Zijlstra
2019-02-14 16:18 ` Brian Gerst
2019-02-14 19:34 ` Peter Zijlstra
2019-02-15 14:34 ` Brian Gerst
2019-02-15 17:18 ` Linus Torvalds
2019-02-15 17:40 ` Peter Zijlstra
2019-02-15 18:28 ` Andy Lutomirski
2019-02-15 23:34 ` Peter Zijlstra
2019-02-16 0:21 ` Linus Torvalds
2019-02-16 10:32 ` Peter Zijlstra
2019-02-16 4:06 ` hpa
2019-02-16 10:30 ` Peter Zijlstra
2019-02-18 22:30 ` H. Peter Anvin
2019-02-19 0:24 ` Linus Torvalds
2019-02-19 2:20 ` Andy Lutomirski
2019-02-19 2:46 ` H. Peter Anvin
2019-02-19 9:07 ` Julien Thierry
2019-02-19 8:53 ` Julien Thierry
2019-02-19 9:15 ` Peter Zijlstra
2019-02-19 9:19 ` Peter Zijlstra
2019-02-19 9:04 ` Peter Zijlstra
2019-02-19 9:21 ` hpa
2019-02-19 9:44 ` Peter Zijlstra
2019-02-19 11:38 ` Thomas Gleixner
2019-02-19 11:58 ` Peter Zijlstra
2019-02-19 12:48 ` Will Deacon
2019-02-20 22:55 ` H. Peter Anvin
2019-02-21 12:06 ` Julien Thierry
2019-02-21 21:35 ` Thomas Gleixner
2019-02-21 22:08 ` Linus Torvalds
2019-02-22 12:58 ` Peter Zijlstra
2019-02-22 18:10 ` Thomas Gleixner
2019-02-22 22:26 ` [RFC][PATCH] objtool: STAC/CLAC validation Peter Zijlstra
2019-02-22 23:34 ` Linus Torvalds
2019-02-23 8:43 ` Peter Zijlstra
2019-02-22 23:39 ` hpa
2019-02-23 8:39 ` Peter Zijlstra
2019-02-25 8:47 ` hpa
2019-02-25 13:21 ` Peter Zijlstra
2019-03-01 15:07 ` Peter Zijlstra
2019-02-25 8:49 ` hpa
2019-02-22 23:55 ` Andy Lutomirski
2019-02-23 8:37 ` Peter Zijlstra
2019-02-23 10:52 ` Peter Zijlstra
2019-02-25 10:51 ` Peter Zijlstra
2019-02-25 11:53 ` Peter Zijlstra
2019-02-25 15:36 ` Andy Lutomirski
2019-02-23 0:34 ` Andy Lutomirski
2019-02-23 1:12 ` Linus Torvalds
2019-02-23 1:16 ` Andy Lutomirski
2019-02-23 1:33 ` Linus Torvalds
2019-02-23 1:40 ` Linus Torvalds
2019-02-25 8:33 ` Julien Thierry
2019-02-25 11:55 ` Peter Zijlstra
2019-02-21 12:46 ` [PATCH] sched/x86: Save [ER]FLAGS on context switch Will Deacon
2019-02-21 22:06 ` Andy Lutomirski
2019-02-18 9:03 ` [PATCH v2] " Peter Zijlstra
2019-02-13 23:19 ` [PATCH v3 3/4] uaccess: Check no rescheduling function is called in unsafe region Linus Torvalds
2019-01-15 13:58 ` [PATCH v3 4/4] arm64: uaccess: Implement user_access_region_active Julien Thierry
2019-01-25 14:27 ` [PATCH v3 0/4] uaccess: Add unsafe accessors for arm64 Catalin Marinas
2019-01-30 16:17 ` Julien Thierry
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