linux-kernel - Re: [PATCH] fork.c: copy_process(): fix cleanup WRT perf_event_free

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Date:	Sat, 27 Sep 2014 20:07:25 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Sylvain 'ythier' Hitier" <sylvain.hitier@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] fork.c: copy_process(): fix cleanup WRT
	perf_event_free_task()

On 09/26, Sylvain 'ythier' Hitier wrote:
>
>     retval = sched_fork(clone_flags, p);
>     if (retval)
> //                                      // mustn't perf_event_free_task()
>         goto bad_fork_cleanup_policy;

Agreed, this is wrong. Good catch.

but, unless I missed something,

>     retval = perf_event_init_task(p);
>     if (retval)
> //                                      // mustn't perf_event_free_task()
                                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

this is not right and thus the patch is not right too.

Suppose that perf_event_init_task() -> perf_event_init_context(ctxn => 0)
succeeds and then perf_event_init_context(ctxn => 1) fails, we need
perf_event_free_task() to cleanup ->perf_event_ctxp[0].

So if perf_event_init_task() fails, we still need "goto bad_fork_cleanup_perf".

No?

Or, probably better, we need to change perf_event_init_context() to call
perf_event_free_task() on failure.

Or. We can simply move memset(child->perf_event_ctxp, 0, ...) from
perf_event_init_context() up. This reminds that we really need to cleanup
copy_process(), in particular I think it asks for the new copy_xxx() helper
which should do misc simple initializations which can't fail.

What do you think?

Oleg.

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