linux-kernel - Re: [PATCH] mm/list_lru.c: use cond_resched

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Date:   Mon, 12 Jun 2017 15:11:12 +0200
From:   Jan Kara <jack@...e.cz>
To:     Sahitya Tummala <stummala@...eaurora.org>
Cc:     Alexander Polakov <apolyakov@...et.ru>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Jan Kara <jack@...e.cz>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] mm/list_lru.c: use cond_resched_lock() for nlru->lock

On Mon 12-06-17 06:17:20, Sahitya Tummala wrote:
> __list_lru_walk_one() can hold the spin lock for longer duration
> if there are more number of entries to be isolated.
> 
> This results in "BUG: spinlock lockup suspected" in the below path -
> 
> [<ffffff8eca0fb0bc>] spin_bug+0x90
> [<ffffff8eca0fb220>] do_raw_spin_lock+0xfc
> [<ffffff8ecafb7798>] _raw_spin_lock+0x28
> [<ffffff8eca1ae884>] list_lru_add+0x28
> [<ffffff8eca1f5dac>] dput+0x1c8
> [<ffffff8eca1eb46c>] path_put+0x20
> [<ffffff8eca1eb73c>] terminate_walk+0x3c
> [<ffffff8eca1eee58>] path_lookupat+0x100
> [<ffffff8eca1f00fc>] filename_lookup+0x6c
> [<ffffff8eca1f0264>] user_path_at_empty+0x54
> [<ffffff8eca1e066c>] SyS_faccessat+0xd0
> [<ffffff8eca084e30>] el0_svc_naked+0x24
> 
> This nlru->lock has been acquired by another CPU in this path -
> 
> [<ffffff8eca1f5fd0>] d_lru_shrink_move+0x34
> [<ffffff8eca1f6180>] dentry_lru_isolate_shrink+0x48
> [<ffffff8eca1aeafc>] __list_lru_walk_one.isra.10+0x94
> [<ffffff8eca1aec34>] list_lru_walk_node+0x40
> [<ffffff8eca1f6620>] shrink_dcache_sb+0x60
> [<ffffff8eca1e56a8>] do_remount_sb+0xbc
> [<ffffff8eca1e583c>] do_emergency_remount+0xb0
> [<ffffff8eca0ba510>] process_one_work+0x228
> [<ffffff8eca0bb158>] worker_thread+0x2e0
> [<ffffff8eca0c040c>] kthread+0xf4
> [<ffffff8eca084dd0>] ret_from_fork+0x10
> 
> Link: http://marc.info/?t=149511514800002&r=1&w=2
> Fix-suggested-by: Jan kara <jack@...e.cz>
> Signed-off-by: Sahitya Tummala <stummala@...eaurora.org>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  mm/list_lru.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/list_lru.c b/mm/list_lru.c
> index 5d8dffd..1af0709 100644
> --- a/mm/list_lru.c
> +++ b/mm/list_lru.c
> @@ -249,6 +249,8 @@ restart:
>  		default:
>  			BUG();
>  		}
> +		if (cond_resched_lock(&nlru->lock))
> +			goto restart;
>  	}
>  
>  	spin_unlock(&nlru->lock);
> -- 
> Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR