linux-kernel - Re: [PATCH v2 1/2] kthread: allocate kthread structure using kmalloc

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Message-ID: <20161024164218.GT3102@twins.programming.kicks-ass.net>
Date:   Mon, 24 Oct 2016 18:42:18 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Roman Pen <roman.penyaev@...fitbricks.com>
Cc:     Andy Lutomirski <luto@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Tejun Heo <tj@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] kthread: allocate kthread structure using kmalloc

On Mon, Oct 24, 2016 at 06:08:13PM +0200, Roman Pen wrote:
> This patch avoids allocation of kthread structure on a stack, and simply
> uses kmalloc.  Allocation on a stack became a huge problem (with memory
> corruption and all other not nice consequences) after the commit 2deb4be28

2deb4be28077 ("x86/dumpstack: When OOPSing, rewind the stack before do_exit()")

Is the normal quoting style.

.gitconfig:

[core]
        abbrev = 12
[alias]
        one = show -s --pretty='format:%h (\"%s\")'

> by Andy Lutomirski, which rewinds the stack on oops, thus ooopsed kthread
> steps on a garbage memory while completion of task->vfork_done structure
> on the following path:
> 
>        oops_end()
>        rewind_stack_do_exit()
>        exit_mm()
>        mm_release()
>        complete_vfork_done()
> 
> Also in this patch two structures 'struct kthread_create_info' and
> 'struct kthread' are merged into one 'struct kthread' and its freeing
> is controlled by a reference counter.
> 
> The last reference on kthread is put from a task work, the callback,
> which is invoked from do_exit().  The major thing is that the last
> put is happens *after* completion_vfork_done() is invoked.
>