linux-kernel - Re: [PATCH 2/5] sched: always use blk_schedule_flush_plug in io_schedule

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Date:	Fri, 01 May 2015 13:42:02 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Shaohua Li <shli@...com>
Cc:	<linux-kernel@...r.kernel.org>, <axboe@...com>, <hch@....de>,
	<neilb@...e.de>
Subject: Re: [PATCH 2/5] sched: always use blk_schedule_flush_plug in io_schedule_out

Shaohua Li <shli@...com> writes:

> block plug callback could sleep, so we introduce a parameter
> 'from_schedule' and corresponding drivers can use it to destinguish a
> schedule plug flush or a plug finish. Unfortunately io_schedule_out
> still uses blk_flush_plug(). This causes below output (Note, I added a
> might_sleep() in raid1_unplug to make it trigger faster, but the whole
> thing doesn't matter if I add might_sleep). In raid1/10, this can cause
> deadlock.
>
> This patch makes io_schedule_out always uses blk_schedule_flush_plug.
> This should only impact drivers (as far as I know, raid 1/10) which are
> sensitive to the 'from_schedule' parameter.

Why wouldn't you change io_schedule_timeout to use blk_flush_plug_list
instead?

Cheers,
Jeff

>
> [  370.817949] ------------[ cut here ]------------
> [  370.817960] WARNING: CPU: 7 PID: 145 at ../kernel/sched/core.c:7306 __might_sleep+0x7f/0x90()
> [  370.817969] do not call blocking ops when !TASK_RUNNING; state=2 set at [<ffffffff81092fcf>] prepare_to_wait+0x2f/0x90
> [  370.817971] Modules linked in: raid1
> [  370.817976] CPU: 7 PID: 145 Comm: kworker/u16:9 Tainted: G        W       4.0.0+ #361
> [  370.817977] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20140709_153802- 04/01/2014
> [  370.817983] Workqueue: writeback bdi_writeback_workfn (flush-9:1)
> [  370.817985]  ffffffff81cd83be ffff8800ba8cb298 ffffffff819dd7af 0000000000000001
> [  370.817988]  ffff8800ba8cb2e8 ffff8800ba8cb2d8 ffffffff81051afc ffff8800ba8cb2c8
> [  370.817990]  ffffffffa00061a8 000000000000041e 0000000000000000 ffff8800ba8cba28
> [  370.817993] Call Trace:
> [  370.817999]  [<ffffffff819dd7af>] dump_stack+0x4f/0x7b
> [  370.818002]  [<ffffffff81051afc>] warn_slowpath_common+0x8c/0xd0
> [  370.818004]  [<ffffffff81051b86>] warn_slowpath_fmt+0x46/0x50
> [  370.818006]  [<ffffffff81092fcf>] ? prepare_to_wait+0x2f/0x90
> [  370.818008]  [<ffffffff81092fcf>] ? prepare_to_wait+0x2f/0x90
> [  370.818010]  [<ffffffff810776ef>] __might_sleep+0x7f/0x90
> [  370.818014]  [<ffffffffa0000c03>] raid1_unplug+0xd3/0x170 [raid1]
> [  370.818024]  [<ffffffff81421d9a>] blk_flush_plug_list+0x8a/0x1e0
> [  370.818028]  [<ffffffff819e3550>] ? bit_wait+0x50/0x50
> [  370.818031]  [<ffffffff819e21b0>] io_schedule_timeout+0x130/0x140
> [  370.818033]  [<ffffffff819e3586>] bit_wait_io+0x36/0x50
> [  370.818034]  [<ffffffff819e31b5>] __wait_on_bit+0x65/0x90
> [  370.818041]  [<ffffffff8125b67c>] ? ext4_read_block_bitmap_nowait+0xbc/0x630
> [  370.818043]  [<ffffffff819e3550>] ? bit_wait+0x50/0x50
> [  370.818045]  [<ffffffff819e3302>] out_of_line_wait_on_bit+0x72/0x80
> [  370.818047]  [<ffffffff810935e0>] ? autoremove_wake_function+0x40/0x40
> [  370.818050]  [<ffffffff811de744>] __wait_on_buffer+0x44/0x50
> [  370.818053]  [<ffffffff8125ae80>] ext4_wait_block_bitmap+0xe0/0xf0
> [  370.818058]  [<ffffffff812975d6>] ext4_mb_init_cache+0x206/0x790
> [  370.818062]  [<ffffffff8114bc6c>] ? lru_cache_add+0x1c/0x50
> [  370.818064]  [<ffffffff81297c7e>] ext4_mb_init_group+0x11e/0x200
> [  370.818066]  [<ffffffff81298231>] ext4_mb_load_buddy+0x341/0x360
> [  370.818068]  [<ffffffff8129a1a3>] ext4_mb_find_by_goal+0x93/0x2f0
> [  370.818070]  [<ffffffff81295b54>] ? ext4_mb_normalize_request+0x1e4/0x5b0
> [  370.818072]  [<ffffffff8129ab67>] ext4_mb_regular_allocator+0x67/0x460
> [  370.818074]  [<ffffffff81295b54>] ? ext4_mb_normalize_request+0x1e4/0x5b0
> [  370.818076]  [<ffffffff8129ca4b>] ext4_mb_new_blocks+0x4cb/0x620
> [  370.818079]  [<ffffffff81290956>] ext4_ext_map_blocks+0x4c6/0x14d0
> [  370.818081]  [<ffffffff812a4d4e>] ? ext4_es_lookup_extent+0x4e/0x290
> [  370.818085]  [<ffffffff8126399d>] ext4_map_blocks+0x14d/0x4f0
> [  370.818088]  [<ffffffff81266fbd>] ext4_writepages+0x76d/0xe50
> [  370.818094]  [<ffffffff81149691>] do_writepages+0x21/0x50
> [  370.818097]  [<ffffffff811d5c00>] __writeback_single_inode+0x60/0x490
> [  370.818099]  [<ffffffff811d630a>] writeback_sb_inodes+0x2da/0x590
> [  370.818103]  [<ffffffff811abf4b>] ? trylock_super+0x1b/0x50
> [  370.818105]  [<ffffffff811abf4b>] ? trylock_super+0x1b/0x50
> [  370.818107]  [<ffffffff811d665f>] __writeback_inodes_wb+0x9f/0xd0
> [  370.818109]  [<ffffffff811d69db>] wb_writeback+0x34b/0x3c0
> [  370.818111]  [<ffffffff811d70df>] bdi_writeback_workfn+0x23f/0x550
> [  370.818116]  [<ffffffff8106bbd8>] process_one_work+0x1c8/0x570
> [  370.818117]  [<ffffffff8106bb5b>] ? process_one_work+0x14b/0x570
> [  370.818119]  [<ffffffff8106c09b>] worker_thread+0x11b/0x470
> [  370.818121]  [<ffffffff8106bf80>] ? process_one_work+0x570/0x570
> [  370.818124]  [<ffffffff81071868>] kthread+0xf8/0x110
> [  370.818126]  [<ffffffff81071770>] ? kthread_create_on_node+0x210/0x210
> [  370.818129]  [<ffffffff819e9322>] ret_from_fork+0x42/0x70
> [  370.818131]  [<ffffffff81071770>] ? kthread_create_on_node+0x210/0x210
> [  370.818132] ---[ end trace 7b4deb71e68b6605 ]---
>
> Cc: NeilBrown <neilb@...e.de>
> Signed-off-by: Shaohua Li <shli@...com>
> ---
>  kernel/sched/core.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index f9123a8..fef7eb2 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4397,21 +4397,17 @@ EXPORT_SYMBOL_GPL(yield_to);
>   */
>  long __sched io_schedule_timeout(long timeout)
>  {
> -	int old_iowait = current->in_iowait;
>  	struct rq *rq;
>  	long ret;
>  
>  	current->in_iowait = 1;
> -	if (old_iowait)
> -		blk_schedule_flush_plug(current);
> -	else
> -		blk_flush_plug(current);
> +	blk_schedule_flush_plug(current);
>  
>  	delayacct_blkio_start();
>  	rq = raw_rq();
>  	atomic_inc(&rq->nr_iowait);
>  	ret = schedule_timeout(timeout);
> -	current->in_iowait = old_iowait;
> +	current->in_iowait = 0;
>  	atomic_dec(&rq->nr_iowait);
>  	delayacct_blkio_end();
--
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