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Date:   Tue, 27 Aug 2019 19:50:02 -0300
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Daniel Vetter <daniel.vetter@ffwll.ch>
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>,
        Christian =?utf-8?B?S8O2bmln?= <christian.koenig@amd.com>,
        =?utf-8?B?SsOpcsO0bWU=?= Glisse <jglisse@redhat.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Wei Wang <wvw@google.com>,
        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>
Subject: Re: [PATCH 3/5] kernel.h: Add non_block_start/end()
Message-ID: <20190827225002.GB30700@ziepe.ca>
References: <20190826201425.17547-1-daniel.vetter@ffwll.ch>
 <20190826201425.17547-4-daniel.vetter@ffwll.ch>
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> 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?

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

Jason