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From: Andy Lutomirski <luto@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
	Borislav Petkov <bp@alien8.de>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Brian Gerst <brgerst@gmail.com>, Jann Horn <jann@thejh.net>,
	Ingo Molnar <mingo@kernel.org>,
	live-patching@vger.kernel.org
Subject: Re: [PATCH 08/12] x86/dumpstack: Pin the target stack in save_stack_trace_tsk()
Date: Fri, 16 Sep 2016 08:32:44 -0700	[thread overview]
Message-ID: <CALCETrW8=+ZeBPVO4BU86ENC0D5Q6_FcR44Bryosz-RdpAqnqQ@mail.gmail.com> (raw)
In-Reply-To: <20160916153131.GG5016@twins.programming.kicks-ass.net>

On Fri, Sep 16, 2016 at 8:31 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Fri, Sep 16, 2016 at 08:12:40AM -0700, Andy Lutomirski wrote:
>> On Fri, Sep 16, 2016 at 12:47 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>> > On Thu, Sep 15, 2016 at 02:19:38PM -0500, Josh Poimboeuf wrote:
>
>> >> My idea was to use task_rq_lock() to lock the runqueue and then check
>> >> tsk->on_cpu.  I think Peter wasn't too keen on it.
>> >
>> > That basically allows a DoS on the scheduler, since a user can run tasks
>> > on every cpu (through sys_sched_setaffinity()). Then doing while (1) cat
>> > /proc/$PID/stack would saturate the rq->lock on every CPU.
>> >
>> > The more tasks the merrier.
>>
>> Is this worse than it would be if this code used preempt_disable()
>> (which I think it did until very recently)?
>
> Much worse, since the proposed task_rq_lock() not only disables
> preemption, it also disables IRQs and takes 2 locks. And hogging the
> rq->lock affects other tasks their ability to schedule.
>

Fair enough.

I'm not sure I care quite enough about /proc/PID/stack to personally
dig through the scheduler and find a way to cleanly say "please don't
run this task for a little while".

  reply	other threads:[~2016-09-16 15:33 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-13 21:29 [PATCH 00/12] thread_info cleanups and stack caching Andy Lutomirski
2016-09-13 21:29 ` [PATCH 01/12] x86/asm: Move 'status' from struct thread_info to struct thread_struct Andy Lutomirski
2016-09-15 10:41   ` [tip:x86/asm] x86/asm: Move the thread_info::status field to thread_struct tip-bot for Andy Lutomirski
2016-09-13 21:29 ` [PATCH 02/12] x86/entry: Get rid of pt_regs_to_thread_info() Andy Lutomirski
2016-09-15  6:21   ` Ingo Molnar
2016-09-15 10:42   ` [tip:x86/asm] " tip-bot for Linus Torvalds
2016-09-13 21:29 ` [PATCH 03/12] um: Stop conflating task_struct::stack with thread_info Andy Lutomirski
2016-09-15  6:21   ` Ingo Molnar
2016-09-15 10:42   ` [tip:x86/asm] um/Stop " tip-bot for Linus Torvalds
2016-09-13 21:29 ` [PATCH 04/12] sched: Allow putting thread_info into task_struct Andy Lutomirski
2016-09-15 10:43   ` [tip:x86/asm] sched/core: " tip-bot for Andy Lutomirski
2016-09-13 21:29 ` [PATCH 05/12] x86: Move " Andy Lutomirski
2016-09-15 10:43   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-09-13 21:29 ` [PATCH 06/12] sched: Add try_get_task_stack() and put_task_stack() Andy Lutomirski
2016-09-13 21:29 ` [PATCH 07/12] kthread: to_live_kthread() needs try_get_task_stack() Andy Lutomirski
2016-09-13 21:29 ` [PATCH 08/12] x86/dumpstack: Pin the target stack in save_stack_trace_tsk() Andy Lutomirski
2016-09-14 14:55   ` Josh Poimboeuf
2016-09-14 18:22     ` Andy Lutomirski
2016-09-14 18:35       ` Josh Poimboeuf
2016-09-15 18:04         ` Andy Lutomirski
2016-09-15 18:37           ` Josh Poimboeuf
2016-09-15 18:41             ` Andy Lutomirski
2016-09-15 19:19               ` Josh Poimboeuf
2016-09-16  7:47                 ` Peter Zijlstra
2016-09-16 15:12                   ` Andy Lutomirski
2016-09-16 15:31                     ` Peter Zijlstra
2016-09-16 15:32                       ` Andy Lutomirski [this message]
2016-09-16 16:35                         ` Peter Zijlstra
2016-09-15  6:37   ` Ingo Molnar
     [not found]     ` <CA+55aFxt=HLrELBE=BXUrWdh6LYs4gtu9S=yCruiDffq4HN80w@mail.gmail.com>
2016-09-15  9:27       ` Ingo Molnar
2016-09-13 21:29 ` [PATCH 09/12] x86/process: Pin the target stack in get_wchan() Andy Lutomirski
2016-09-17  2:00   ` Jann Horn
2016-09-22 22:44     ` Andy Lutomirski
2016-09-22 22:50       ` Andy Lutomirski
2016-09-23  7:43       ` Jann Horn
2016-09-23 18:28         ` Kees Cook
2016-09-23 18:34           ` Jann Horn
2016-09-26  5:10             ` Tycho Andersen
2016-09-13 21:29 ` [PATCH 10/12] lib/syscall: Pin the task stack in collect_syscall() Andy Lutomirski
2016-09-13 21:29 ` [PATCH 11/12] sched: Free the stack early if CONFIG_THREAD_INFO_IN_TASK Andy Lutomirski
2016-09-13 21:29 ` [PATCH 12/12] fork: Cache two thread stacks per cpu if CONFIG_VMAP_STACK is set Andy Lutomirski

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