Re: [PATCH v2 1/3] md: Fix undefined behaviour in is_mddev_idle

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On 12/10/2021 3:17 PM, Damien Le Moal wrote:
> On 2021/12/10 15:45, Hannes Reinecke wrote:
>> On 12/10/21 6:17 AM, Li Jinlin wrote:
>>> UBSAN reports this problem:
>>>
>>> [ 5984.281385] UBSAN: Undefined behaviour in drivers/md/md.c:8175:15
>>> [ 5984.281390] signed integer overflow:
>>> [ 5984.281393] -2147483291 - 2072033152 cannot be represented in type 'int'
>>> [ 5984.281400] CPU: 25 PID: 1854 Comm: md101_resync Kdump: loaded Not tainted 4.19.90
>>> [ 5984.281404] Hardware name: Huawei TaiShan 200 (Model 5280)/BC82AMDDA
>>> [ 5984.281406] Call trace:
>>> [ 5984.281415]  dump_backtrace+0x0/0x310
>>> [ 5984.281418]  show_stack+0x28/0x38
>>> [ 5984.281425]  dump_stack+0xec/0x15c
>>> [ 5984.281430]  ubsan_epilogue+0x18/0x84
>>> [ 5984.281434]  handle_overflow+0x14c/0x19c
>>> [ 5984.281439]  __ubsan_handle_sub_overflow+0x34/0x44
>>> [ 5984.281445]  is_mddev_idle+0x338/0x3d8
>>> [ 5984.281449]  md_do_sync+0x1bb8/0x1cf8
>>> [ 5984.281452]  md_thread+0x220/0x288
>>> [ 5984.281457]  kthread+0x1d8/0x1e0
>>> [ 5984.281461]  ret_from_fork+0x10/0x18
>>>
>>> When the stat aacum of the disk is greater than INT_MAX, its
>>> value becomes negative after casting to 'int', which may lead
>>> to overflow after subtracting a positive number. In the same
>>> way, when the value of sync_io is greater than INT_MAX,
>>> overflow may also occur. These situations will lead to
>>> undefined behavior.
>>>
>>> Otherwise, if the stat accum of the disk is close to INT_MAX
>>> when creating raid arrays, the initial value of last_events
>>> would be set close to INT_MAX when mddev initializes IO
>>> event counters. 'curr_events - rdev->last_events > 64' will
>>> always false during synchronization. If all the disks of mddev
>>> are in this case, is_mddev_idle() will always return 1, which
>>> may cause non-sync IO is very slow.
>>>
>>> To address these problems, need to use 64bit signed integer
>>> type for sync_io, last_events, and curr_events.
>>>
>>> In all the drivers that come with the kernel, the sync_io
>>> variable in struct gendisk is only used for the md driver
>>> currently. It should be more suitable in struct md_rdev, so
>>> add the sync_io variable in struct md_rdev, and use it to
>>> replace. We modify md_sync_acct() and md_sync_acct_bio()
>>> to fit for this change as well. md_sync_acct_bio() need
>>> access to the rdev, so we set bio->bi_bdev to rdev before
>>> calling it, and reset bio->bi_bdev to bdev in this function.
>>>
>> Please make that two patches, one for moving sync_io and one for
>> fixing the undefined behaviour.

ok.

>>
>>> Signed-off-by: Li Jinlin <lijinlin3@xxxxxxxxxx>
>>> ---
>>>   drivers/md/md.c       |  6 +++---
>>>   drivers/md/md.h       | 13 +++++++++----
>>>   drivers/md/raid1.c    |  4 ++--
>>>   drivers/md/raid10.c   | 24 ++++++++++++------------
>>>   drivers/md/raid5.c    |  4 ++--
>>>   include/linux/genhd.h |  1 -
>>>   6 files changed, 28 insertions(+), 24 deletions(-)
>>>
>>> diff --git a/drivers/md/md.c b/drivers/md/md.c
>>> index 5111ed966947..f1b71a92801e 100644
>>> --- a/drivers/md/md.c
>>> +++ b/drivers/md/md.c
>>> @@ -8429,14 +8429,14 @@ static int is_mddev_idle(struct mddev *mddev, int init)
>>>   {
>>>   	struct md_rdev *rdev;
>>>   	int idle;
>>> -	int curr_events;
>>> +	s64 curr_events;
>>>   
>>>   	idle = 1;
>>>   	rcu_read_lock();
>>>   	rdev_for_each_rcu(rdev, mddev) {
>>>   		struct gendisk *disk = rdev->bdev->bd_disk;
>>> -		curr_events = (int)part_stat_read_accum(disk->part0, sectors) -
>>> -			      atomic_read(&disk->sync_io);
>>> +		curr_events = (s64)part_stat_read_accum(disk->part0, sectors) -
>>> +			      atomic64_read(&rdev->sync_io);
>>
>> So you are replacing a 'signed integer' (ie 32bit) calculation with a 
>> 'signed 64-bit integer' calculation.
>> IE you just shifted the overflow from INT_MAX to LONG_MAX, without 
>> actually fixing it, or?

Yes, for the disk with 512-byte sector sizes, the data size of INT_MAX
sectors is 1T. LONG_MAX is enough to use until the server restarts,
and overflow will not occur anymore.

>>
>>>   		/* sync IO will cause sync_io to increase before the disk_stats
>>>   		 * as sync_io is counted when a request starts, and
>>>   		 * disk_stats is counted when it completes.
>>> diff --git a/drivers/md/md.h b/drivers/md/md.h
>>> index 53ea7a6961de..584e357e0940 100644
>>> --- a/drivers/md/md.h
>>> +++ b/drivers/md/md.h
>>> @@ -50,7 +50,7 @@ struct md_rdev {
>>>   
>>>   	sector_t sectors;		/* Device size (in 512bytes sectors) */
>>>   	struct mddev *mddev;		/* RAID array if running */
>>> -	int last_events;		/* IO event timestamp */
>>> +	s64 last_events;		/* IO event timestamp */
>>>   
>>>   	/*
>>>   	 * If meta_bdev is non-NULL, it means that a separate device is
>>> @@ -138,6 +138,8 @@ struct md_rdev {
>>>   		unsigned int size;	/* Size in sectors of the PPL space */
>>>   		sector_t sector;	/* First sector of the PPL space */
>>>   	} ppl;
>>> +
>>> +	atomic64_t sync_io;		/* counter of sync IO (unit sectors) */
>>>   };
>>>   enum flag_bits {
>>>   	Faulty,			/* device is known to have a fault */
>>> @@ -549,14 +551,17 @@ static inline int mddev_trylock(struct mddev *mddev)
>>>   }
>>>   extern void mddev_unlock(struct mddev *mddev);
>>>   
>>> -static inline void md_sync_acct(struct block_device *bdev, unsigned long nr_sectors)
>>> +static inline void md_sync_acct(struct md_rdev *rdev, unsigned long nr_sectors)
>>>   {
>>> -	atomic_add(nr_sectors, &bdev->bd_disk->sync_io);
>>> +	atomic64_add(nr_sectors, &rdev->sync_io);
>>>   }
>>>   
>>>   static inline void md_sync_acct_bio(struct bio *bio, unsigned long nr_sectors)
>>>   {
>>> -	md_sync_acct(bio->bi_bdev, nr_sectors);
>>> +	struct md_rdev *rdev = (void *)bio->bi_bdev;
>>
>> That look weird. bio->bi_bdev should be a 'struct gendisk', not a MD 
>> internal data structure.
> 
> You mean a "struct block_device". right ? :)
> 

Here is a difficult point for moving sync_io. We need a good way
to slove it or not move sync_io.

>>
>>> +
>>> +	bio_set_dev(bio, rdev->bdev);
>>> +	md_sync_acct(rdev, nr_sectors);
>>>   }
>>>   
>>>   struct md_personality
>>> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
>>> index 7dc8026cf6ee..74c42dabe57c 100644
>>> --- a/drivers/md/raid1.c
>>> +++ b/drivers/md/raid1.c
>>> @@ -2232,7 +2232,7 @@ static void sync_request_write(struct mddev *mddev, struct r1bio *r1_bio)
>>>   
>>>   		wbio->bi_end_io = end_sync_write;
>>>   		atomic_inc(&r1_bio->remaining);
>>> -		md_sync_acct(conf->mirrors[i].rdev->bdev, bio_sectors(wbio));
>>> +		md_sync_acct(conf->mirrors[i].rdev, bio_sectors(wbio));
>>>   
>>>   		submit_bio_noacct(wbio);
>>>   	}
>>> @@ -2791,7 +2791,7 @@ static sector_t raid1_sync_request(struct mddev *mddev, sector_t sector_nr,
>>>   		if (rdev && bio->bi_end_io) {
>>>   			atomic_inc(&rdev->nr_pending);
>>>   			bio->bi_iter.bi_sector = sector_nr + rdev->data_offset;
>>> -			bio_set_dev(bio, rdev->bdev);
>>> +			bio->bi_bdev = (void *)rdev;
>>>   			if (test_bit(FailFast, &rdev->flags))
>>>   				bio->bi_opf |= MD_FAILFAST;
>>>   		}
>>> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
>>> index dde98f65bd04..fc1e6c0996de 100644
>>> --- a/drivers/md/raid10.c
>>> +++ b/drivers/md/raid10.c
>>> @@ -2407,7 +2407,7 @@ static void sync_request_write(struct mddev *mddev, struct r10bio *r10_bio)
>>>   
>>>   		atomic_inc(&conf->mirrors[d].rdev->nr_pending);
>>>   		atomic_inc(&r10_bio->remaining);
>>> -		md_sync_acct(conf->mirrors[d].rdev->bdev, bio_sectors(tbio));
>>> +		md_sync_acct(conf->mirrors[d].rdev, bio_sectors(tbio));
>>>   
>>>   		if (test_bit(FailFast, &conf->mirrors[d].rdev->flags))
>>>   			tbio->bi_opf |= MD_FAILFAST;
>>> @@ -2430,7 +2430,7 @@ static void sync_request_write(struct mddev *mddev, struct r10bio *r10_bio)
>>>   			bio_copy_data(tbio, fbio);
>>>   		d = r10_bio->devs[i].devnum;
>>>   		atomic_inc(&r10_bio->remaining);
>>> -		md_sync_acct(conf->mirrors[d].replacement->bdev,
>>> +		md_sync_acct(conf->mirrors[d].replacement,
>>>   			     bio_sectors(tbio));
>>>   		submit_bio_noacct(tbio);
>>>   	}
>>> @@ -2562,12 +2562,12 @@ static void recovery_request_write(struct mddev *mddev, struct r10bio *r10_bio)
>>>   		wbio2 = NULL;
>>>   	if (wbio->bi_end_io) {
>>>   		atomic_inc(&conf->mirrors[d].rdev->nr_pending);
>>> -		md_sync_acct(conf->mirrors[d].rdev->bdev, bio_sectors(wbio));
>>> +		md_sync_acct(conf->mirrors[d].rdev, bio_sectors(wbio));
>>>   		submit_bio_noacct(wbio);
>>>   	}
>>>   	if (wbio2) {
>>>   		atomic_inc(&conf->mirrors[d].replacement->nr_pending);
>>> -		md_sync_acct(conf->mirrors[d].replacement->bdev,
>>> +		md_sync_acct(conf->mirrors[d].replacement,
>>>   			     bio_sectors(wbio2));
>>>   		submit_bio_noacct(wbio2);
>>>   	}
>>> @@ -3486,7 +3486,7 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
>>>   				from_addr = r10_bio->devs[j].addr;
>>>   				bio->bi_iter.bi_sector = from_addr +
>>>   					rdev->data_offset;
>>> -				bio_set_dev(bio, rdev->bdev);
>>> +				bio->bi_bdev = (void *)rdev;
>>>   				atomic_inc(&rdev->nr_pending);
>>>   				/* and we write to 'i' (if not in_sync) */
>>>   
>>> @@ -3508,7 +3508,7 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
>>>   					bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
>>>   					bio->bi_iter.bi_sector = to_addr
>>>   						+ mrdev->data_offset;
>>> -					bio_set_dev(bio, mrdev->bdev);
>>> +					bio->bi_bdev = (void *)mrdev;
>>>   					atomic_inc(&r10_bio->remaining);
>>>   				} else
>>>   					r10_bio->devs[1].bio->bi_end_io = NULL;
>>> @@ -3529,7 +3529,7 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
>>>   				bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
>>>   				bio->bi_iter.bi_sector = to_addr +
>>>   					mreplace->data_offset;
>>> -				bio_set_dev(bio, mreplace->bdev);
>>> +				bio->bi_bdev = (void *)mreplace;
>>>   				atomic_inc(&r10_bio->remaining);
>>>   				break;
>>>   			}
>>> @@ -3684,7 +3684,7 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
>>>   			if (test_bit(FailFast, &rdev->flags))
>>>   				bio->bi_opf |= MD_FAILFAST;
>>>   			bio->bi_iter.bi_sector = sector + rdev->data_offset;
>>> -			bio_set_dev(bio, rdev->bdev);
>>> +			bio->bi_bdev = (void *)rdev;
>>>   			count++;
>>>   
>>>   			rdev = rcu_dereference(conf->mirrors[d].replacement);
>>> @@ -3706,7 +3706,7 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
>>>   			if (test_bit(FailFast, &rdev->flags))
>>>   				bio->bi_opf |= MD_FAILFAST;
>>>   			bio->bi_iter.bi_sector = sector + rdev->data_offset;
>>> -			bio_set_dev(bio, rdev->bdev);
>>> +			bio->bi_bdev = (void *)rdev;
>>>   			count++;
>>>   			rcu_read_unlock();
>>>   		}
>>> @@ -4865,7 +4865,7 @@ static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr,
>>>   
>>>   	read_bio = bio_alloc_bioset(GFP_KERNEL, RESYNC_PAGES, &mddev->bio_set);
>>>   
>>> -	bio_set_dev(read_bio, rdev->bdev);
>>> +	read_bio->bi_bdev = (void *)rdev;
>>>   	read_bio->bi_iter.bi_sector = (r10_bio->devs[r10_bio->read_slot].addr
>>>   			       + rdev->data_offset);
>>>   	read_bio->bi_private = r10_bio;
>>> @@ -4921,7 +4921,7 @@ static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr,
>>>   		if (!rdev2 || test_bit(Faulty, &rdev2->flags))
>>>   			continue;
>>>   
>>> -		bio_set_dev(b, rdev2->bdev);
>>> +		b->bi_bdev = (void *)rdev2;
>>>   		b->bi_iter.bi_sector = r10_bio->devs[s/2].addr +
>>>   			rdev2->new_data_offset;
>>>   		b->bi_end_io = end_reshape_write;
>>> @@ -5016,7 +5016,7 @@ static void reshape_request_write(struct mddev *mddev, struct r10bio *r10_bio)
>>>   		}
>>>   		atomic_inc(&rdev->nr_pending);
>>>   		rcu_read_unlock();
>>> -		md_sync_acct_bio(b, r10_bio->sectors);
>>> +		md_sync_acct(rdev, r10_bio->sectors);
>>>   		atomic_inc(&r10_bio->remaining);
>>>   		b->bi_next = NULL;
>>>   		submit_bio_noacct(b);
>>> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
>>> index 9c1a5877cf9f..b932282ff50a 100644
>>> --- a/drivers/md/raid5.c
>>> +++ b/drivers/md/raid5.c
>>> @@ -1167,7 +1167,7 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
>>>   		if (rdev) {
>>>   			if (s->syncing || s->expanding || s->expanded
>>>   			    || s->replacing)
>>> -				md_sync_acct(rdev->bdev, RAID5_STRIPE_SECTORS(conf));
>>> +				md_sync_acct(rdev, RAID5_STRIPE_SECTORS(conf));
>>>   
>>>   			set_bit(STRIPE_IO_STARTED, &sh->state);
>>>   
>>> @@ -1234,7 +1234,7 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
>>>   		if (rrdev) {
>>>   			if (s->syncing || s->expanding || s->expanded
>>>   			    || s->replacing)
>>> -				md_sync_acct(rrdev->bdev, RAID5_STRIPE_SECTORS(conf));
>>> +				md_sync_acct(rrdev, RAID5_STRIPE_SECTORS(conf));
>>>   
>>>   			set_bit(STRIPE_IO_STARTED, &sh->state);
>>>   
>>> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
>>> index 74c410263113..6b84444111e4 100644
>>> --- a/include/linux/genhd.h
>>> +++ b/include/linux/genhd.h
>>> @@ -150,7 +150,6 @@ struct gendisk {
>>>   	struct list_head slave_bdevs;
>>>   #endif
>>>   	struct timer_rand_state *random;
>>> -	atomic_t sync_io;		/* RAID */
>>>   	struct disk_events *ev;
>>>   #ifdef  CONFIG_BLK_DEV_INTEGRITY
>>>   	struct kobject integrity_kobj;
>>>
>>
>> Cheers,
>>
>> Hannes
> 
> 
Thanks,
JinLin



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