[Drbd-dev] [PATCH v2 1/3] md: Fix undefined behaviour in is_mddev_idle
Damien Le Moal
damien.lemoal at opensource.wdc.com
Fri Dec 10 08:17:09 CET 2021
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.
>
>> Signed-off-by: Li Jinlin <lijinlin3 at huawei.com>
>> ---
>> 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?
>
>> /* 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 ? :)
>
>> +
>> + 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
--
Damien Le Moal
Western Digital Research
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