linux-kernel - Re: [PATCH] sched: Avoid that __wait_on_bit

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Date:	Wed, 10 Aug 2016 12:58:42 -0700
From:	Bart Van Assche <bart.vanassche@...disk.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Johannes Weiner" <hannes@...xchg.org>, Neil Brown <neilb@...e.de>,
	Michael Shaver <jmshaver@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: Avoid that __wait_on_bit_lock() hangs

On 08/10/2016 03:46 AM, Oleg Nesterov wrote:
> OK. Could you  try another debugging patch below?
>
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index e5a3244..9d5f892 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -711,6 +711,15 @@ static inline int page_has_private(struct page *page)
>  	return !!(page->flags & PAGE_FLAGS_PRIVATE);
>  }
>
> +void unlock_page(struct page *page);
> +static inline void __ClearPageLocked_x(struct page *page)
> +{
> +	if (PageLocked(compound_head(page)))
> +		unlock_page(page);
> +}
> +
> +#define __ClearPageLocked(page)	__ClearPageLocked_x(page)
> +
>  #undef PF_ANY
>  #undef PF_HEAD
>  #undef PF_NO_TAIL

Hello Oleg,

That's an excellent catch. With your previous patch and this patch 
applied I can't reproduce the hang in truncate_inode_pages_range() 
anymore. I still see some other wait_on_page_bit() hangs after an I/O 
error has occurred. However, the hangs that I still see are related to 
waiting on buffer head state changes and not on the PG_locked page flag.

Thanks,

Bart.