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From:   Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Wed, 28 Aug 2019 20:33:13 +0200
Message-ID: <CAKMK7uHKiLwXLHd1xThZVM1dH-oKrtpDZ=FxLBBwtY7XmJKgtA@mail.gmail.com>
Subject: Re: [PATCH 3/5] kernel.h: Add non_block_start/end()
To:     Jason Gunthorpe <jgg@ziepe.ca>
Cc:     LKML <linux-kernel@vger.kernel.org>, Linux MM <linux-mm@kvack.org>,
        DRI Development <dri-devel@lists.freedesktop.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>,
        David Rientjes <rientjes@google.com>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
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        Masahiro Yamada <yamada.masahiro@socionext.com>,
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        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jann Horn <jannh@google.com>, Feng Tang <feng.tang@intel.com>,
        Kees Cook <keescook@chromium.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Daniel Vetter <daniel.vetter@intel.com>
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On Wed, Aug 28, 2019 at 12:50 AM Jason Gunthorpe <jgg@ziepe.ca> wrote:
>
> > diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> > index 4fa360a13c1e..82f84cfe372f 100644
> > +++ b/include/linux/kernel.h
> > @@ -217,7 +217,9 @@ extern void __cant_sleep(const char *file, int line, int preempt_offset);
> >   * might_sleep - annotation for functions that can sleep
> >   *
> >   * this macro will print a stack trace if it is executed in an atomic
> > - * context (spinlock, irq-handler, ...).
> > + * context (spinlock, irq-handler, ...). Additional sections where blocking is
> > + * not allowed can be annotated with non_block_start() and non_block_end()
> > + * pairs.
> >   *
> >   * This is a useful debugging help to be able to catch problems early and not
> >   * be bitten later when the calling function happens to sleep when it is not
> > @@ -233,6 +235,25 @@ extern void __cant_sleep(const char *file, int line, int preempt_offset);
> >  # define cant_sleep() \
> >       do { __cant_sleep(__FILE__, __LINE__, 0); } while (0)
> >  # define sched_annotate_sleep()      (current->task_state_change = 0)
> > +/**
> > + * non_block_start - annotate the start of section where sleeping is prohibited
> > + *
> > + * This is on behalf of the oom reaper, specifically when it is calling the mmu
> > + * notifiers. The problem is that if the notifier were to block on, for example,
> > + * mutex_lock() and if the process which holds that mutex were to perform a
> > + * sleeping memory allocation, the oom reaper is now blocked on completion of
> > + * that memory allocation. Other blocking calls like wait_event() pose similar
> > + * issues.
> > + */
> > +# define non_block_start() \
> > +     do { current->non_block_count++; } while (0)
> > +/**
> > + * non_block_end - annotate the end of section where sleeping is prohibited
> > + *
> > + * Closes a section opened by non_block_start().
> > + */
> > +# define non_block_end() \
> > +     do { WARN_ON(current->non_block_count-- == 0); } while (0)
>
> check-patch does not like these, and I agree
>
> #101: FILE: include/linux/kernel.h:248:
> +# define non_block_start() \
> +       do { current->non_block_count++; } while (0)
>
> /tmp/tmp1spfxufy/0006-kernel-h-Add-non_block_start-end-.patch:108: WARNING: Single statement macros should not use a do {} while (0) loop
> #108: FILE: include/linux/kernel.h:255:
> +# define non_block_end() \
> +       do { WARN_ON(current->non_block_count-- == 0); } while (0)
>
> Please use a static inline?

We need get_current() plus the task_struct, so this gets real messy
real fast. Not even sure which header this would fit in, or whether
I'd need to create a new one. You're insisting on this or respinning
with the do { } while (0) dropped ok.

Thanks, Daniel

> Also, can we get one more ack on this patch?
>
> Jason


-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch