From: Peter Zijlstra <peterz@infradead.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Kees Cook <keescook@chromium.org>,
x86@kernel.org, linux-kernel@vger.kernel.org,
juri.lelli@redhat.com, vincent.guittot@linaro.org,
dietmar.eggemann@arm.com, rostedt@goodmis.org,
bsegall@google.com, mgorman@suse.de, bristot@redhat.com,
akpm@linux-foundation.org, zhengqi.arch@bytedance.com,
linux@armlinux.org.uk, catalin.marinas@arm.com, will@kernel.org,
mpe@ellerman.id.au, paul.walmsley@sifive.com, palmer@dabbelt.com,
hca@linux.ibm.com, gor@linux.ibm.com, borntraeger@de.ibm.com,
linux-arch@vger.kernel.org, ardb@kernel.org
Subject: Re: [PATCH 2/7] stacktrace,sched: Make stack_trace_save_tsk() more robust
Date: Fri, 22 Oct 2021 19:01:35 +0200 [thread overview]
Message-ID: <20211022170135.GF174703@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20211022165431.GF86184@C02TD0UTHF1T.local>
On Fri, Oct 22, 2021 at 05:54:31PM +0100, Mark Rutland wrote:
> > Pardon my thin understanding of the scheduler, but I assume this change
> > doesn't mean stack_trace_save_tsk() stops working for "current", right?
> > In trying to answer this for myself, I couldn't convince myself what value
> > current->__state have here. Is it one of TASK_(UN)INTERRUPTIBLE ?
>
> Regardless of that, current->on_rq will be non-zero, so you're right that this
> causes stack_trace_save_tsk() to not work for current, e.g.
>
> | # cat /proc/self/stack
> | # wc /proc/self/stack
> | 0 0 0 /proc/self/stack
>
> TBH, I think that (taking a step back from this issue in particular)
> stack_trace_save_tsk() *shouldn't* work for current, and callers *should* be
> forced to explicitly handle current separately from blocked tasks.
That..
>
> So we could fix this in the stacktrace code with:
>
> | diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
> | index a1cdbf8c3ef8..327af9ff2c55 100644
> | --- a/kernel/stacktrace.c
> | +++ b/kernel/stacktrace.c
> | @@ -149,7 +149,10 @@ unsigned int stack_trace_save_tsk(struct task_struct *tsk, unsigned long *store,
> | .skip = skipnr + (current == tsk),
> | };
> |
> | - task_try_func(tsk, try_arch_stack_walk_tsk, &c);
> | + if (tsk == current)
> | + try_arch_stack_walk_tsk(tsk, &c);
> | + else
> | + task_try_func(tsk, try_arch_stack_walk_tsk, &c);
> |
> | return c.len;
> | }
>
> ... and we could rename task_try_func() to blocked_task_try_func(), and
> later push the distinction into higher-level callers.
I think I favour this fix if we have to. But that's for next week :-)
next prev parent reply other threads:[~2021-10-22 17:02 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-22 15:09 [PATCH 0/7] arch: More wchan fixes Peter Zijlstra
2021-10-22 15:09 ` [PATCH 1/7] x86: Fix __get_wchan() for !STACKTRACE Peter Zijlstra
2021-10-22 16:25 ` Kees Cook
2021-10-26 19:16 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-10-22 15:09 ` [PATCH 2/7] stacktrace,sched: Make stack_trace_save_tsk() more robust Peter Zijlstra
2021-10-22 16:25 ` Kees Cook
2021-10-22 16:45 ` Peter Zijlstra
2021-10-22 16:57 ` Mark Rutland
2021-10-22 16:54 ` Mark Rutland
2021-10-22 17:01 ` Peter Zijlstra [this message]
2021-10-25 20:38 ` Peter Zijlstra
2021-10-25 20:52 ` Kees Cook
2021-10-26 9:33 ` Mark Rutland
2021-10-25 16:27 ` Peter Zijlstra
2021-10-22 15:09 ` [PATCH 3/7] ARM: implement ARCH_STACKWALK Peter Zijlstra
2021-10-22 16:18 ` Kees Cook
2021-10-22 15:09 ` [PATCH 4/7] arch: Make ARCH_STACKWALK independent of STACKTRACE Peter Zijlstra
2021-10-22 16:18 ` Kees Cook
2021-10-22 16:36 ` Peter Zijlstra
2021-10-22 17:06 ` Mark Rutland
2021-10-22 15:09 ` [PATCH 5/7] powerpc, arm64: Mark __switch_to() as __sched Peter Zijlstra
2021-10-22 16:15 ` Kees Cook
2021-10-22 17:40 ` Mark Rutland
2021-10-22 15:09 ` [PATCH 6/7] arch: __get_wchan() || ARCH_STACKWALK Peter Zijlstra
2021-10-22 16:13 ` Kees Cook
2021-10-22 17:52 ` Mark Rutland
2021-10-22 15:09 ` [PATCH 7/7] selftests: proc: Make sure wchan works when it exists Peter Zijlstra
2021-10-22 15:27 ` [PATCH 0/7] arch: More wchan fixes Peter Zijlstra
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