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

From: Hannes Reinecke
Date: Fri Dec 10 2021 - 01:46:06 EST

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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@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?

/* 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.

+
+ 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
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@xxxxxxx +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

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In reply to: Li Jinlin: "[PATCH v2 1/3] md: Fix undefined behaviour in is_mddev_idle"
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