Date:	Wed, 22 Apr 2009 13:17:21 -0500
From:	Steve Wise <swise@...ngridcomputing.com>
To:	Jens Axboe <jens.axboe@...cle.com>
CC:	balbir@...ux.vnet.ibm.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Wolfram Strepp <wstrepp@....de>
Subject: Re: [BUG] rbtree bug with mmotm 2009-04-14-17-24

Jens Axboe wrote:
>>
>> Don't bother, I see what the bug is now. It's caused by commit
>> a36e71f996e25d6213f57951f7ae1874086ec57e and it's due to ->ioprio being
>> changed without the prio rb root being adjusted.
>>
>> I'll provide a fix shortly.
>>     
>
> Quick'n dirty, I think this should fix the issue.
>
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index 7e13f04..79ebb4c 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -594,7 +594,7 @@ cfq_prio_tree_lookup(struct cfq_data *cfqd, int ioprio, sector_t sector,
>  
>  static void cfq_prio_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq)
>  {
> -	struct rb_root *root = &cfqd->prio_trees[cfqq->ioprio];
> +	struct rb_root *root = &cfqd->prio_trees[cfqq->org_ioprio];
>  	struct rb_node **p, *parent;
>  	struct cfq_queue *__cfqq;
>  
> @@ -606,8 +606,8 @@ static void cfq_prio_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq)
>  	if (!cfqq->next_rq)
>  		return;
>  
> -	__cfqq = cfq_prio_tree_lookup(cfqd, cfqq->ioprio, cfqq->next_rq->sector,
> -					 &parent, &p);
> +	__cfqq = cfq_prio_tree_lookup(cfqd, cfqq->org_ioprio,
> +					cfqq->next_rq->sector, &parent, &p);
>  	BUG_ON(__cfqq);
>  
>  	rb_link_node(&cfqq->p_node, parent, p);
> @@ -656,8 +656,10 @@ static void cfq_del_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
>  
>  	if (!RB_EMPTY_NODE(&cfqq->rb_node))
>  		cfq_rb_erase(&cfqq->rb_node, &cfqd->service_tree);
> -	if (!RB_EMPTY_NODE(&cfqq->p_node))
> -		rb_erase_init(&cfqq->p_node, &cfqd->prio_trees[cfqq->ioprio]);
> +	if (!RB_EMPTY_NODE(&cfqq->p_node)) {
> +		rb_erase_init(&cfqq->p_node,
> +					&cfqd->prio_trees[cfqq->org_ioprio]);
> +	}
>  
>  	BUG_ON(!cfqd->busy_queues);
>  	cfqd->busy_queues--;
> @@ -976,7 +978,7 @@ static struct cfq_queue *cfqq_close(struct cfq_data *cfqd,
>  	 * First, if we find a request starting at the end of the last
>  	 * request, choose it.
>  	 */
> -	__cfqq = cfq_prio_tree_lookup(cfqd, cur_cfqq->ioprio,
> +	__cfqq = cfq_prio_tree_lookup(cfqd, cur_cfqq->org_ioprio,
>  				      sector, &parent, NULL);
>  	if (__cfqq)
>  		return __cfqq;
> @@ -1559,8 +1561,9 @@ cfq_alloc_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
>  
>  static void cfq_init_prio_data(struct cfq_queue *cfqq, struct io_context *ioc)
>  {
> +	struct cfq_data *cfqd = cfqq->cfqd;
>  	struct task_struct *tsk = current;
> -	int ioprio_class;
> +	int ioprio_class, prio_readd = 0;
>  
>  	if (!cfq_cfqq_prio_changed(cfqq))
>  		return;
> @@ -1592,12 +1595,24 @@ static void cfq_init_prio_data(struct cfq_queue *cfqq, struct io_context *ioc)
>  	}
>  
>  	/*
> +	 * Remove us from the prio_tree if we are present, since we index
> +	 * by ->org_ioprio
> +	 */
> +	if (!RB_EMPTY_NODE(&cfqq->p_node)) {
> +		rb_erase(&cfqq->p_node, &cfqd->prio_trees[cfqq->org_ioprio]);
> +		prio_readd = 1;
> +	}
> +
> +	/*
>  	 * keep track of original prio settings in case we have to temporarily
>  	 * elevate the priority of this queue
>  	 */
>  	cfqq->org_ioprio = cfqq->ioprio;
>  	cfqq->org_ioprio_class = cfqq->ioprio_class;
>  	cfq_clear_cfqq_prio_changed(cfqq);
> +
> +	if (prio_readd)
> +		cfq_prio_tree_add(cfqd, cfqq);
>  }
>  
>  static void changed_ioprio(struct io_context *ioc, struct cfq_io_context *cic)
>
>   

Still crashes:

Starting udev: BUG: unable to handle kernel NULL pointer dereference at 
(null)
IP: [<ffffffff8034ee05>] rb_erase+0x130/0x2a7
PGD 12cd05067 PUD 12e09f067 PMD 0
Oops: 0000 [#1] SMP
last sysfs file: /sys/block/sda/sda3/dev
CPU 0
Modules linked in: snd_hda_codec_intelhdmi snd_hda_codec_realtek 
snd_hda_intel snd_hda_codec snd_seq_dummy snd_seq_oss snd_seq_midi_event 
snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss snd_pcm cxgb3 r8169 
snd_timer snd sg sr_mod cdrom rtc_cmos rtc_core button i2c_i801 
serio_raw floppy soundcore shpchp mii rtc_lib i2c_core snd_page_alloc 
pcspkr dm_snapshot dm_zero dm_mirror dm_region_hash dm_log dm_mod 
ata_piix libata sd_mod scsi_mod ext3 jbd uhci_hcd ohci_hcd ehci_hcd
Pid: 2381, comm: vol_id Not tainted 2.6.30-rc2-jens #11 P5E-VM HDMI
RIP: 0010:[<ffffffff8034ee05>]  [<ffffffff8034ee05>] rb_erase+0x130/0x2a7
RSP: 0018:ffff88012cc7f7f8  EFLAGS: 00010046
RAX: ffff88012cde2a21 RBX: ffff88012cde2a20 RCX: 0000000000000000
RDX: ffff88012cde2a20 RSI: ffff88012d421e30 RDI: 0000000000000000
RBP: ffff88012cc7f808 R08: 0000000000000000 R09: ffff88012d421e30
R10: ffff88012fb8a140 R11: ffff88012f03e3c0 R12: ffff88012d421e30
R13: ffff88012d421e00 R14: ffff88012cde2630 R15: 0000000000000000
FS:  00000000006e3880(0063) GS:ffff88002804b000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000000000000000 CR3: 000000012b454000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process vol_id (pid: 2381, threadinfo ffff88012cc7e000, task 
ffff88012a901530)
Stack:
 ffff88012cde2660 ffff88012d5a1788 ffff88012cc7f828 ffffffff8034690d
 ffff88012cc7f828 ffff88012cde2630 ffff88012cc7f868 ffffffff803478e5
 ffff88012d421e00 ffff88012cde2630 ffff88012d5a1788 ffff88012d421e00
Call Trace:
 [<ffffffff8034690d>] rb_erase_init+0x11/0x21
 [<ffffffff803478e5>] cfq_remove_request+0x184/0x1e6
 [<ffffffff80347993>] cfq_dispatch_insert+0x4c/0x70
 [<ffffffff80348618>] cfq_dispatch_requests+0x2fb/0x40a
 [<ffffffff8033b344>] elv_next_request+0x193/0x1a8
 [<ffffffff8034c1e1>] ? kobject_get+0x1a/0x22
 [<ffffffffa005fe52>] scsi_request_fn+0x7a/0x496 [scsi_mod]
 [<ffffffff8033d720>] blk_start_queueing+0x1a/0x23
 [<ffffffff80347d2a>] cfq_insert_request+0x244/0x385
 [<ffffffff8033b46a>] elv_insert+0x111/0x1bd
 [<ffffffff8033b5ac>] __elv_add_request+0x96/0x9e
 [<ffffffff8033e306>] __make_request+0x3c2/0x400
 [<ffffffff802efb2e>] ? proc_pid_instantiate+0x87/0x9c
 [<ffffffff8033ca9b>] generic_make_request+0x27f/0x319
 [<ffffffff802cd91e>] ? bio_init+0x18/0x32
 [<ffffffff8033df3b>] submit_bio+0xb4/0xbd
 [<ffffffff802c9970>] submit_bh+0xe5/0x109
 [<ffffffff802cc659>] block_read_full_page+0x261/0x27f
 [<ffffffff802cfd5e>] ? blkdev_get_block+0x0/0x4e
 [<ffffffff802cefc3>] blkdev_readpage+0x13/0x15
 [<ffffffff80285329>] __do_page_cache_readahead+0x134/0x16c
 [<ffffffff8028552d>] ondemand_readahead+0x143/0x155
 [<ffffffff802855d7>] page_cache_sync_readahead+0x17/0x19
 [<ffffffff8027ecac>] generic_file_aio_read+0x245/0x594
 [<ffffffff802abff4>] do_sync_read+0xe2/0x126
 [<ffffffff8028f553>] ? __do_fault+0x362/0x3ac
 [<ffffffff8024c30c>] ? autoremove_wake_function+0x0/0x38
 [<ffffffff8029104c>] ? handle_mm_fault+0x1d9/0x6d1
 [<ffffffff8031a144>] ? security_file_permission+0x11/0x13
 [<ffffffff802ac748>] vfs_read+0xab/0x134
 [<ffffffff802acae9>] sys_read+0x47/0x70
 [<ffffffff8020ba2b>] system_call_fastpath+0x16/0x1b
Code: eb 0a 48 89 4a 08 eb 04 49 89 0c 24 41 ff c8 0f 85 88 01 00 00 e9 
4b 01 00 00 48 8b 7b 10 48 39 cf 0f 85 a1 00 00 00 48 8b 7b 08 <48> 8b 
07 a8 01 75 1a 48 83 c8 01 4c 89 e6 48 89 07 48 83 23 fe
RIP  [<ffffffff8034ee05>] rb_erase+0x130/0x2a7
 RSP <ffff88012cc7f7f8>
CR2: 0000000000000000
---[ end trace 98881b739b7ec57a ]---

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