linux-kernel - Re: [PATCH] mm: cond_resched in tlb_flush_mmu to fix soft lockups on !CONFIG

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Date:	Tue, 18 Dec 2012 13:01:09 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Michal Hocko <mhocko@...e.cz>
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] mm: cond_resched in tlb_flush_mmu to fix soft lockups
 on !CONFIG_PREEMPT

On 12/18/2012 11:11 AM, Michal Hocko wrote:
> Since e303297 (mm: extended batches for generic mmu_gather) we are batching
> pages to be freed until either tlb_next_batch cannot allocate a new batch or we
> are done.
>
> This works just fine most of the time but we can get in troubles with
> non-preemptible kernel (CONFIG_PREEMPT_NONE or CONFIG_PREEMPT_VOLUNTARY) on
> large machines where too aggressive batching might lead to soft lockups during
> process exit path (exit_mmap) because there are no scheduling points down the
> free_pages_and_swap_cache path and so the freeing can take long enough to
> trigger the soft lockup.
>
> The lockup is harmless except when the system is setup to panic on
> softlockup which is not that unusual.
>
> The simplest way to work around this issue is to explicitly cond_resched per
> batch in tlb_flush_mmu (1020 pages on x86_64).

> Signed-off-by: Michal Hocko <mhocko@...e.cz>
> Cc: stable@...r.kernel.org # 3.0 and higher

Reviewed-by: Rik van Riel <riel@...hat.com>

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