Re: [PATCH 2/7] block: Remove bio->bi_ioc

[Jens Axboe <axboe@kernel.dk>]

On 11/20/18 10:21 AM, Ming Lei wrote:
> On Mon, Nov 19, 2018 at 12:51:26PM +0900, Damien Le Moal wrote:
>> bio->bi_ioc is never set so always NULL. Remove references to it in
>> bio_disassociate_task() and in rq_ioc() and delete this field from
>> struct bio. With this change, rq_ioc() always returns
>> current->io_context without the need for a bio argument. Further
>> simplify the code and make it more readable by also removing this
>> helper, which also allows to simplify blk_mq_sched_assign_ioc() by
>> removing its bio argument.
>>
>> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
>> ---
>>  block/bio.c               |  4 ----
>>  block/blk-core.c          |  2 +-
>>  block/blk-mq-sched.c      |  4 ++--
>>  block/blk-mq-sched.h      |  2 +-
>>  block/blk-mq.c            |  4 ++--
>>  block/blk.h               | 16 ----------------
>>  include/linux/blk_types.h |  3 +--
>>  7 files changed, 7 insertions(+), 28 deletions(-)
>>
>> diff --git a/block/bio.c b/block/bio.c
>> index 4f4d9884443b..03895cc0d74a 100644
>> --- a/block/bio.c
>> +++ b/block/bio.c
>> @@ -2027,10 +2027,6 @@ int bio_associate_blkg(struct bio *bio, struct blkcg_gq *blkg)
>>   */
>>  void bio_disassociate_task(struct bio *bio)
>>  {
>> -	if (bio->bi_ioc) {
>> -		put_io_context(bio->bi_ioc);
>> -		bio->bi_ioc = NULL;
>> -	}
>>  	if (bio->bi_css) {
>>  		css_put(bio->bi_css);
>>  		bio->bi_css = NULL;
>> diff --git a/block/blk-core.c b/block/blk-core.c
>> index d6e8ab9ca99d..492648c96992 100644
>> --- a/block/blk-core.c
>> +++ b/block/blk-core.c
>> @@ -813,7 +813,7 @@ unsigned int blk_plug_queued_count(struct request_queue *q)
>>  
>>  void blk_init_request_from_bio(struct request *req, struct bio *bio)
>>  {
>> -	struct io_context *ioc = rq_ioc(bio);
>> +	struct io_context *ioc = current->io_context;
>>  
>>  	if (bio->bi_opf & REQ_RAHEAD)
>>  		req->cmd_flags |= REQ_FAILFAST_MASK;
>> diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
>> index d084f731d104..13b8dc332541 100644
>> --- a/block/blk-mq-sched.c
>> +++ b/block/blk-mq-sched.c
>> @@ -31,10 +31,10 @@ void blk_mq_sched_free_hctx_data(struct request_queue *q,
>>  }
>>  EXPORT_SYMBOL_GPL(blk_mq_sched_free_hctx_data);
>>  
>> -void blk_mq_sched_assign_ioc(struct request *rq, struct bio *bio)
>> +void blk_mq_sched_assign_ioc(struct request *rq)
>>  {
>>  	struct request_queue *q = rq->q;
>> -	struct io_context *ioc = rq_ioc(bio);
>> +	struct io_context *ioc = current->io_context;
>>  	struct io_cq *icq;
>>  
>>  	spin_lock_irq(&q->queue_lock);
>> diff --git a/block/blk-mq-sched.h b/block/blk-mq-sched.h
>> index 7ff5671bf128..0f719c8532ae 100644
>> --- a/block/blk-mq-sched.h
>> +++ b/block/blk-mq-sched.h
>> @@ -8,7 +8,7 @@
>>  void blk_mq_sched_free_hctx_data(struct request_queue *q,
>>  				 void (*exit)(struct blk_mq_hw_ctx *));
>>  
>> -void blk_mq_sched_assign_ioc(struct request *rq, struct bio *bio);
>> +void blk_mq_sched_assign_ioc(struct request *rq);
>>  
>>  void blk_mq_sched_request_inserted(struct request *rq);
>>  bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index 32b246ed44c0..636f80b96fa6 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -389,8 +389,8 @@ static struct request *blk_mq_get_request(struct request_queue *q,
>>  	if (!op_is_flush(data->cmd_flags)) {
>>  		rq->elv.icq = NULL;
>>  		if (e && e->type->ops.prepare_request) {
>> -			if (e->type->icq_cache && rq_ioc(bio))
>> -				blk_mq_sched_assign_ioc(rq, bio);
>> +			if (e->type->icq_cache)
>> +				blk_mq_sched_assign_ioc(rq);
>>  
>>  			e->type->ops.prepare_request(rq, bio);
>>  			rq->rq_flags |= RQF_ELVPRIV;
>> diff --git a/block/blk.h b/block/blk.h
>> index 816a9abb87cd..610948157a5b 100644
>> --- a/block/blk.h
>> +++ b/block/blk.h
>> @@ -254,22 +254,6 @@ void ioc_clear_queue(struct request_queue *q);
>>  
>>  int create_task_io_context(struct task_struct *task, gfp_t gfp_mask, int node);
>>  
>> -/**
>> - * rq_ioc - determine io_context for request allocation
>> - * @bio: request being allocated is for this bio (can be %NULL)
>> - *
>> - * Determine io_context to use for request allocation for @bio.  May return
>> - * %NULL if %current->io_context doesn't exist.
>> - */
>> -static inline struct io_context *rq_ioc(struct bio *bio)
>> -{
>> -#ifdef CONFIG_BLK_CGROUP
>> -	if (bio && bio->bi_ioc)
>> -		return bio->bi_ioc;
>> -#endif
>> -	return current->io_context;
>> -}
>> -
>>  /**
>>   * create_io_context - try to create task->io_context
>>   * @gfp_mask: allocation mask
>> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
>> index dbdbfbd6a987..c0ba1a038ff3 100644
>> --- a/include/linux/blk_types.h
>> +++ b/include/linux/blk_types.h
>> @@ -174,10 +174,9 @@ struct bio {
>>  	void			*bi_private;
>>  #ifdef CONFIG_BLK_CGROUP
>>  	/*
>> -	 * Optional ioc and css associated with this bio.  Put on bio
>> +	 * Optional css associated with this bio.  Put on bio
>>  	 * release.  Read comment on top of bio_associate_current().
>>  	 */
>> -	struct io_context	*bi_ioc;
>>  	struct cgroup_subsys_state *bi_css;
>>  	struct blkcg_gq		*bi_blkg;
>>  	struct bio_issue	bi_issue;
> 
> Hi,
> 
> Just found the following kernel oops, seems it is likely related with this
> patch.
> 
> [  391.981012] BUG: unable to handle kernel NULL pointer dereference at 0000000000000038
> [  391.982506] PGD 0 P4D 0
> [  391.982975] Oops: 0000 [#1] PREEMPT SMP PTI
> [  391.983769] CPU: 1 PID: 1790 Comm: scsi_id Not tainted 4.20.0-rc3_72abead3bf43_for-4.21-block-mp-bvec-V11+ #1
> [  391.985563] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.10.2-2.fc27 04/01/2014
> [  391.987107] RIP: 0010:ioc_lookup_icq+0x13/0x54
> [  391.987936] Code: f6 48 8b 3d 1c 78 5b 01 5b 5d 41 5c 41 5d 41 5e 41 5f e9 68 bd eb ff 0f 1f 44 00 00 55 53 48 89 fb 51 48 89 f5 e8 e3 82 da ff <48> 8b 43 38 48 85 c0 74 05 48 39 28 74 22 48 63 b5 8c 00 00 00 48
> [  391.991318] RSP: 0018:ffffc90001467bb0 EFLAGS: 00010002
> [  391.992292] RAX: ffff888266c85ac0 RBX: 0000000000000000 RCX: 0000000000000100
> [  391.993615] RDX: 0000000000000001 RSI: ffff88826601f230 RDI: 0000000000000000
> [  391.994917] RBP: ffff88826601f230 R08: 00000000f461df07 R09: 0000000000000006
> [  391.996242] R10: ffffc90001467b10 R11: 0000000000000020 R12: ffff888269df4000
> [  391.997572] R13: 0000000000000000 R14: ffff88826601f2c4 R15: 0000000000000001
> [  391.998905] FS:  00007fa6923b7940(0000) GS:ffff888277a80000(0000) knlGS:0000000000000000
> [  392.000389] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  392.001468] CR2: 0000000000000038 CR3: 0000000106dd8005 CR4: 0000000000760ee0
> [  392.002783] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [  392.004108] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [  392.005394] PKRU: 55555554
> [  392.005897] Call Trace:
> [  392.006384]  blk_mq_sched_assign_ioc+0x3d/0x7f
> [  392.007216]  blk_mq_get_request+0x321/0x354
> [  392.008008]  blk_mq_alloc_request+0x4e/0xbf
> [  392.008802]  blk_get_request+0x24/0x4c
> [  392.009518]  sg_io+0x93/0x371
> [  392.010074]  ? bd_acquire+0xa6/0xa6
> [  392.010707]  ? dput+0x29/0xfd
> [  392.011232]  ? mntput_no_expire+0x11/0x185
> [  392.011987]  scsi_cmd_ioctl+0x1d3/0x386
> [  392.012707]  sd_ioctl+0xbb/0xde [sd_mod]
> [  392.013449]  blkdev_ioctl+0x893/0x8bf
> [  392.014132]  block_ioctl+0x3c/0x3f
> [  392.014781]  vfs_ioctl+0x1e/0x2b
> [  392.015378]  do_vfs_ioctl+0x531/0x559
> [  392.016059]  ksys_ioctl+0x3e/0x5d
> [  392.016681]  __x64_sys_ioctl+0x16/0x19
> [  392.017361]  do_syscall_64+0x84/0x13f
> [  392.018060]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [  392.018995] RIP: 0033:0x7fa691edf267
> [  392.019663] Code: b3 66 90 48 8b 05 19 3c 2c 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d e9 3b 2c 00 f7 d8 64 89 01 48
> [  392.023072] RSP: 002b:00007ffe463e8de8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> [  392.024457] RAX: ffffffffffffffda RBX: 00007ffe463e8e20 RCX: 00007fa691edf267
> [  392.025767] RDX: 00007ffe463e8e20 RSI: 0000000000002285 RDI: 0000000000000004
> [  392.027068] RBP: 00007ffe463e9470 R08: 0000000000002006 R09: 00000000fffffe00
> [  392.028413] R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffe463e9920
> [  392.029722] R13: 00007ffe463e8e20 R14: 00007ffe463e8e2a R15: 00007ffe463e9920
> [  392.031031] Modules linked in: scsi_debug null_blk isofs iTCO_wdt iTCO_vendor_support i2c_i801 i2c_core lpc_ich mfd_core ip_tables sr_mod cdrom usb_storage sd_mod ahci libahci libata crc32c_intel virtio_scsi qemu_fw_cfg dm_mirror dm_region_hash dm_log dm_mod [last unloaded: null_blk]
> [  392.035573] Dumping ftrace buffer:
> [  392.036203]    (ftrace buffer empty)
> [  392.036871] CR2: 0000000000000038
> [  392.037503] ---[ end trace fa20a1088b068790 ]---

I think the below should fix it, we haven't necessarily setup an
ioc if we're just doing as passthrough request.


diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 13b8dc332541..f096d8989773 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -34,9 +34,16 @@ EXPORT_SYMBOL_GPL(blk_mq_sched_free_hctx_data);
 void blk_mq_sched_assign_ioc(struct request *rq)
 {
 	struct request_queue *q = rq->q;
-	struct io_context *ioc = current->io_context;
+	struct io_context *ioc;
 	struct io_cq *icq;
 
+	/*
+	 * May not have an IO context if it's a passthrough request
+	 */
+	ioc = current->io_context;
+	if (!ioc)
+		return;
+
 	spin_lock_irq(&q->queue_lock);
 	icq = ioc_lookup_icq(ioc, q);
 	spin_unlock_irq(&q->queue_lock);

-- 
Jens Axboe