Re: [PATCH 3/5] kernel.h: Add non_block_start/end()

[Jason Gunthorpe]

> 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