When some buggy driver doesn't set its queue->limits.discard_granularity
(e.g. current loop device driver), discard at LBA 0 on such device will
trigger a kernel BUG() panic from block/blk-mq.c:563.
[ 955.565006][ C39] ------------[ cut here ]------------
[ 955.559660][ C39] invalid opcode: 0000 [#1] SMP NOPTI
[ 955.622171][ C39] CPU: 39 PID: 248 Comm: ksoftirqd/39 Tainted: G E 5.8.0-default+ #40
[ 955.622171][ C39] Hardware name: Lenovo ThinkSystem SR650 -[7X05CTO1WW]-/-[7X05CTO1WW]-, BIOS -[IVE160M-2.70]- 07/17/2020
[ 955.622175][ C39] RIP: 0010:blk_mq_end_request+0x107/0x110
[ 955.622177][ C39] Code: 48 8b 03 e9 59 ff ff ff 48 89 df 5b 5d 41 5c e9 9f ed ff ff 48 8b 35 98 3c f4 00 48 83 c7 10 48 83 c6 19 e8 cb 56 c9 ff eb cb <0f> 0b 0f 1f 80 00 00 00 00 0f 1f 44 00 00 55 48 89 e5 41 56 41 54
[ 955.622179][ C39] RSP: 0018:ffffb1288701fe28 EFLAGS: 00010202
[ 955.749277][ C39] RAX: 0000000000000001 RBX: ffff956fffba5080 RCX: 0000000000004003
[ 955.749278][ C39] RDX: 0000000000000003 RSI: 0000000000000000 RDI: 0000000000000000
[ 955.749279][ C39] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
[ 955.749279][ C39] R10: ffffb1288701fd28 R11: 0000000000000001 R12: ffffffffa8e05160
[ 955.749280][ C39] R13: 0000000000000004 R14: 0000000000000004 R15: ffffffffa7ad3a1e
[ 955.749281][ C39] FS: 0000000000000000(0000) GS:ffff95bfbda00000(0000) knlGS:0000000000000000
[ 955.749282][ C39] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 955.749282][ C39] CR2: 00007f6f0ef766a8 CR3: 0000005a37012002 CR4: 00000000007606e0
[ 955.749283][ C39] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 955.749284][ C39] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 955.749284][ C39] PKRU: 55555554
[ 955.749285][ C39] Call Trace:
[ 955.749290][ C39] blk_done_softirq+0x99/0xc0
[ 957.550669][ C39] __do_softirq+0xd3/0x45f
[ 957.550677][ C39] ? smpboot_thread_fn+0x2f/0x1e0
[ 957.550679][ C39] ? smpboot_thread_fn+0x74/0x1e0
[ 957.550680][ C39] ? smpboot_thread_fn+0x14e/0x1e0
[ 957.550684][ C39] run_ksoftirqd+0x30/0x60
[ 957.550687][ C39] smpboot_thread_fn+0x149/0x1e0
[ 957.886225][ C39] ? sort_range+0x20/0x20
[ 957.886226][ C39] kthread+0x137/0x160
[ 957.886228][ C39] ? kthread_park+0x90/0x90
[ 957.886231][ C39] ret_from_fork+0x22/0x30
[ 959.117120][ C39] ---[ end trace 3dacdac97e2ed164 ]---
This is the procedure to reproduce the panic,
# modprobe scsi_debug delay=0 dev_size_mb=2048 max_queue=1
# losetup -f /dev/nvme0n1 --direct-io=on
# blkdiscard /dev/loop0 -o 0 -l 0x200
This is how the BUG() panic triggered by __blkdev_issue_discard(),
- For a NVMe SSD backing loop device, the driver does not initialize
its queue->limits.discard_granularity and leaves it to 0.
- When discard on LBA 0 of the loop device, __blkdev_issue_discard()
is called before loop device driver code.
- Inside __blkdev_issue_discard(), when calculating value of
granularity_aligned_lba by
granularity_aligned_lba = round_up(sector_mapped,
q->limits.discard_granularity >> SECTOR_SHIFT);
because sector_mapped is 0 (at LBA 0 and no partition offset), and
q->limits.discard_granularity is 0 (by the buggy loop driver), the
calculated granularity_aligned_lba is 0.
- The inline function bio_aligned_discard_max_sectors() is defined as
return round_down(UINT_MAX, q->limits.discard_granularity) >>
SECTOR_SHIFT;
when q->limits.discard_granularity is 0 from loop device driver, the
above calculation returns value 0.
- Now granularity_aligned_lba and sctor_mapped are 0, req_sectors is
calculated by the following lines in __blkdev_issue_discard(),
if (granularity_aligned_lba == sector_mapped)
req_sects = min_t(sector_t, nr_sects,
bio_aligned_discard_max_sectors(q));
because bio_aligned_discard_max_sectors(q) returns 0, req_sects is
calculated as 0.
- Now a discard bio is mistakenly initialized as a 0 byte bio by,
bio->bi_iter.bi_size = req_sects << 9;
and sent to loop device driver.
- This discard request is handled by loop device driver by following
code path,
loop_handle_cmd => do_req_filebacked => lo_fallocate =>
file->f_op->fallocate => blkdev_fallocate => blkdev_issue_zeroout =>
__blkdev_issue_write_zeroes
- Inside __blkdev_issue_write_zeroes(), a 0 byte length discard bio is
composed and sent to the backing device of the loop device.
- In the I/O completion code path, in my case it is,
blk_done_softirq => nrq->q->mq_ops->complete => nvme_pci_complete_rq
=> nvme_complete_rq => blk_mq_end_request
inside blk_mq_end_request(), blk_update_request() is called and due to
req->bio is NULL in previous step, blk_update_request() returns false
then the BUG() panic in blk_mq_end_request() is triggered.
Although the above panic can be fixed in loop device driver, the generic
__blkdev_issue_discard() should also be fixed to tolerate the incorrect
0 value from queue->limits.discard_granularity, in case some other buggy
driver makes such mistake again.
This patch checks whether q->limits.discard_granularity is 0 in
__blkdev_issue_discard() and bio_aligned_discard_max_sectors(). If it is
0 from some buggy driver queue, prints a warning oops information and
set queue_logical_block_size(q) to a local variable discard_granularity.
This local variable is used in round_up() and round_down() calculation,
now req_sects won't be 0 and no empty discard request is generated.
Fixes: 9b15d109a6b2 ("block: improve discard bio alignment in __blkdev_issue_discard()")
Fixes: c52abf563049 ("loop: Better discard support for block devices")
Reported-by: Ming Lei <[email protected]>
Signed-off-by: Coly Li <[email protected]>
Cc: Hannes Reinecke <[email protected]>
Cc: Ming Lei <[email protected]>
Cc: Xiao Ni <[email protected]>
Cc: Bart Van Assche <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Enzo Matsumiya <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Evan Green <[email protected]>
---
block/blk-lib.c | 8 +++++++-
block/blk.h | 9 +++++++--
2 files changed, 14 insertions(+), 3 deletions(-)
diff --git a/block/blk-lib.c b/block/blk-lib.c
index 019e09bb9c0e..3017e4cba923 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -30,6 +30,7 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
struct bio *bio = *biop;
unsigned int op;
sector_t bs_mask, part_offset = 0;
+ sector_t discard_granularity;
if (!q)
return -ENXIO;
@@ -54,6 +55,11 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
if (!nr_sects)
return -EINVAL;
+ discard_granularity = q->limits.discard_granularity;
+ /* In case some buggy driver does not set limits.discard_granularity */
+ if (WARN_ON_ONCE(discard_granularity == 0))
+ discard_granularity = queue_logical_block_size(q);
+
/* In case the discard request is in a partition */
if (bdev->bd_partno)
part_offset = bdev->bd_part->start_sect;
@@ -63,7 +69,7 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
sector_t sector_mapped = sector + part_offset;
granularity_aligned_lba = round_up(sector_mapped,
- q->limits.discard_granularity >> SECTOR_SHIFT);
+ discard_granularity >> SECTOR_SHIFT);
/*
* Check whether the discard bio starts at a discard_granularity
diff --git a/block/blk.h b/block/blk.h
index 49e2928a1632..b52aa7049fb0 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -274,8 +274,13 @@ static inline unsigned int bio_allowed_max_sectors(struct request_queue *q)
static inline unsigned int bio_aligned_discard_max_sectors(
struct request_queue *q)
{
- return round_down(UINT_MAX, q->limits.discard_granularity) >>
- SECTOR_SHIFT;
+ sector_t discard_granularity = q->limits.discard_granularity;
+
+ /* In case some buggy driver doesn't set >limits.discard_granularity */
+ if (WARN_ON_ONCE(discard_granularity == 0))
+ discard_granularity = queue_logical_block_size(q);
+
+ return round_down(UINT_MAX, discard_granularity) >> SECTOR_SHIFT;
}
/*
--
2.26.2
On 2020/8/4 22:31, Johannes Thumshirn wrote:
> On 04/08/2020 16:23, Coly Li wrote:
>> This is the procedure to reproduce the panic,
>> # modprobe scsi_debug delay=0 dev_size_mb=2048 max_queue=1
>> # losetup -f /dev/nvme0n1 --direct-io=on
>> # blkdiscard /dev/loop0 -o 0 -l 0x200
>
> losetup -f /dev/sdX isn't it?
>
In my case, I use a NVMe SSD as the backing device of the loop device.
Because I don't have a scsi lun.
And loading scsi_debug module seems necessary, otherwise the discard
process just hang and I cannot see the kernel panic (I don't know why yet).
Coly Li
On 04/08/2020 16:34, Coly Li wrote:
> On 2020/8/4 22:31, Johannes Thumshirn wrote:
>> On 04/08/2020 16:23, Coly Li wrote:
>>> This is the procedure to reproduce the panic,
>>> # modprobe scsi_debug delay=0 dev_size_mb=2048 max_queue=1
>>> # losetup -f /dev/nvme0n1 --direct-io=on
>>> # blkdiscard /dev/loop0 -o 0 -l 0x200
>>
>> losetup -f /dev/sdX isn't it?
>>
>
> In my case, I use a NVMe SSD as the backing device of the loop device.
> Because I don't have a scsi lun.
>
> And loading scsi_debug module seems necessary, otherwise the discard
> process just hang and I cannot see the kernel panic (I don't know why yet).
OK, now that's highly interesting. Does it also happen if you back loop with
a file? loop_config_discard() has different cases for the different backing devices/files. S
On 04/08/2020 16:37, Johannes Thumshirn wrote:
> On 04/08/2020 16:34, Coly Li wrote:
>> On 2020/8/4 22:31, Johannes Thumshirn wrote:
>>> On 04/08/2020 16:23, Coly Li wrote:
>>>> This is the procedure to reproduce the panic,
>>>> # modprobe scsi_debug delay=0 dev_size_mb=2048 max_queue=1
>>>> # losetup -f /dev/nvme0n1 --direct-io=on
>>>> # blkdiscard /dev/loop0 -o 0 -l 0x200
>>>
>>> losetup -f /dev/sdX isn't it?
>>>
>>
>> In my case, I use a NVMe SSD as the backing device of the loop device.
>> Because I don't have a scsi lun.
>>
>> And loading scsi_debug module seems necessary, otherwise the discard
>> process just hang and I cannot see the kernel panic (I don't know why yet).
>
> OK, now that's highly interesting. Does it also happen if you back loop with
> a file? loop_config_discard() has different cases for the different backing devices/files. S
>
Damn I didn't want to hit sent....
Does this (untested) change make a difference:
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 475e1a738560..8a07a89d702e 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -895,6 +895,9 @@ static void loop_config_discard(struct loop_device *lo)
blk_queue_max_write_zeroes_sectors(q,
backingq->limits.max_write_zeroes_sectors);
+ q->limits.discard_granularity =
+ backingq->limits.discard_granularity;
+
/*
* We use punch hole to reclaim the free space used by the
* image a.k.a. discard. However we do not support discard if
On 04/08/2020 16:23, Coly Li wrote:
> This is the procedure to reproduce the panic,
> # modprobe scsi_debug delay=0 dev_size_mb=2048 max_queue=1
> # losetup -f /dev/nvme0n1 --direct-io=on
> # blkdiscard /dev/loop0 -o 0 -l 0x200
losetup -f /dev/sdX isn't it?
On 2020/8/4 22:37, Johannes Thumshirn wrote:
> On 04/08/2020 16:34, Coly Li wrote:
>> On 2020/8/4 22:31, Johannes Thumshirn wrote:
>>> On 04/08/2020 16:23, Coly Li wrote:
>>>> This is the procedure to reproduce the panic,
>>>> # modprobe scsi_debug delay=0 dev_size_mb=2048 max_queue=1
>>>> # losetup -f /dev/nvme0n1 --direct-io=on
>>>> # blkdiscard /dev/loop0 -o 0 -l 0x200
>>>
>>> losetup -f /dev/sdX isn't it?
>>>
>>
>> In my case, I use a NVMe SSD as the backing device of the loop device.
>> Because I don't have a scsi lun.
>>
>> And loading scsi_debug module seems necessary, otherwise the discard
>> process just hang and I cannot see the kernel panic (I don't know why yet).
>
> OK, now that's highly interesting. Does it also happen if you back loop with
> a file? loop_config_discard() has different cases for the different backing devices/files. S
>
No, for a file backing, q->limits.discard_granularity is set to
inode->i_sb->s_blocksize. And the encrypted loop device does not support
discard.
Such issue just only happens on a device backing loop device which
announces supporting discard. Without Ming's fix to loop device driver,
discard on LBA 0 will trigger the BUG() panic in my setup (Maybe it is
more easier to trigger this BUG() panic with scsi lun).
Coly Li
On 2020/8/4 22:39, Johannes Thumshirn wrote:
> On 04/08/2020 16:37, Johannes Thumshirn wrote:
>> On 04/08/2020 16:34, Coly Li wrote:
>>> On 2020/8/4 22:31, Johannes Thumshirn wrote:
>>>> On 04/08/2020 16:23, Coly Li wrote:
>>>>> This is the procedure to reproduce the panic,
>>>>> # modprobe scsi_debug delay=0 dev_size_mb=2048 max_queue=1
>>>>> # losetup -f /dev/nvme0n1 --direct-io=on
>>>>> # blkdiscard /dev/loop0 -o 0 -l 0x200
>>>>
>>>> losetup -f /dev/sdX isn't it?
>>>>
>>>
>>> In my case, I use a NVMe SSD as the backing device of the loop device.
>>> Because I don't have a scsi lun.
>>>
>>> And loading scsi_debug module seems necessary, otherwise the discard
>>> process just hang and I cannot see the kernel panic (I don't know why yet).
>>
>> OK, now that's highly interesting. Does it also happen if you back loop with
>> a file? loop_config_discard() has different cases for the different backing devices/files. S
>>
>
> Damn I didn't want to hit sent....
>
> Does this (untested) change make a difference:
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 475e1a738560..8a07a89d702e 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -895,6 +895,9 @@ static void loop_config_discard(struct loop_device *lo)
> blk_queue_max_write_zeroes_sectors(q,
> backingq->limits.max_write_zeroes_sectors);
>
> + q->limits.discard_granularity =
> + backingq->limits.discard_granularity;
> +
> /*
> * We use punch hole to reclaim the free space used by the
> * image a.k.a. discard. However we do not support discard if
>
Yes, Ming just posts a patch with a very similar change to loop device
driver.
Coly Li
On 04/08/2020 16:45, Coly Li wrote:
> Yes, Ming just posts a patch with a very similar change to loop device
> driver.
Ah ok. I'll go and have a look at Ming's patch then.
On Tue, Aug 04, 2020 at 10:23:32PM +0800, Coly Li wrote:
> When some buggy driver doesn't set its queue->limits.discard_granularity
> (e.g. current loop device driver), discard at LBA 0 on such device will
> trigger a kernel BUG() panic from block/blk-mq.c:563.
>
> [ 955.565006][ C39] ------------[ cut here ]------------
> [ 955.559660][ C39] invalid opcode: 0000 [#1] SMP NOPTI
> [ 955.622171][ C39] CPU: 39 PID: 248 Comm: ksoftirqd/39 Tainted: G E 5.8.0-default+ #40
> [ 955.622171][ C39] Hardware name: Lenovo ThinkSystem SR650 -[7X05CTO1WW]-/-[7X05CTO1WW]-, BIOS -[IVE160M-2.70]- 07/17/2020
> [ 955.622175][ C39] RIP: 0010:blk_mq_end_request+0x107/0x110
> [ 955.622177][ C39] Code: 48 8b 03 e9 59 ff ff ff 48 89 df 5b 5d 41 5c e9 9f ed ff ff 48 8b 35 98 3c f4 00 48 83 c7 10 48 83 c6 19 e8 cb 56 c9 ff eb cb <0f> 0b 0f 1f 80 00 00 00 00 0f 1f 44 00 00 55 48 89 e5 41 56 41 54
> [ 955.622179][ C39] RSP: 0018:ffffb1288701fe28 EFLAGS: 00010202
> [ 955.749277][ C39] RAX: 0000000000000001 RBX: ffff956fffba5080 RCX: 0000000000004003
> [ 955.749278][ C39] RDX: 0000000000000003 RSI: 0000000000000000 RDI: 0000000000000000
> [ 955.749279][ C39] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> [ 955.749279][ C39] R10: ffffb1288701fd28 R11: 0000000000000001 R12: ffffffffa8e05160
> [ 955.749280][ C39] R13: 0000000000000004 R14: 0000000000000004 R15: ffffffffa7ad3a1e
> [ 955.749281][ C39] FS: 0000000000000000(0000) GS:ffff95bfbda00000(0000) knlGS:0000000000000000
> [ 955.749282][ C39] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 955.749282][ C39] CR2: 00007f6f0ef766a8 CR3: 0000005a37012002 CR4: 00000000007606e0
> [ 955.749283][ C39] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 955.749284][ C39] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [ 955.749284][ C39] PKRU: 55555554
> [ 955.749285][ C39] Call Trace:
> [ 955.749290][ C39] blk_done_softirq+0x99/0xc0
> [ 957.550669][ C39] __do_softirq+0xd3/0x45f
> [ 957.550677][ C39] ? smpboot_thread_fn+0x2f/0x1e0
> [ 957.550679][ C39] ? smpboot_thread_fn+0x74/0x1e0
> [ 957.550680][ C39] ? smpboot_thread_fn+0x14e/0x1e0
> [ 957.550684][ C39] run_ksoftirqd+0x30/0x60
> [ 957.550687][ C39] smpboot_thread_fn+0x149/0x1e0
> [ 957.886225][ C39] ? sort_range+0x20/0x20
> [ 957.886226][ C39] kthread+0x137/0x160
> [ 957.886228][ C39] ? kthread_park+0x90/0x90
> [ 957.886231][ C39] ret_from_fork+0x22/0x30
> [ 959.117120][ C39] ---[ end trace 3dacdac97e2ed164 ]---
>
> This is the procedure to reproduce the panic,
> # modprobe scsi_debug delay=0 dev_size_mb=2048 max_queue=1
> # losetup -f /dev/nvme0n1 --direct-io=on
> # blkdiscard /dev/loop0 -o 0 -l 0x200
>
> This is how the BUG() panic triggered by __blkdev_issue_discard(),
> - For a NVMe SSD backing loop device, the driver does not initialize
> its queue->limits.discard_granularity and leaves it to 0.
> - When discard on LBA 0 of the loop device, __blkdev_issue_discard()
> is called before loop device driver code.
> - Inside __blkdev_issue_discard(), when calculating value of
> granularity_aligned_lba by
> granularity_aligned_lba = round_up(sector_mapped,
> q->limits.discard_granularity >> SECTOR_SHIFT);
> because sector_mapped is 0 (at LBA 0 and no partition offset), and
> q->limits.discard_granularity is 0 (by the buggy loop driver), the
> calculated granularity_aligned_lba is 0.
> - The inline function bio_aligned_discard_max_sectors() is defined as
> return round_down(UINT_MAX, q->limits.discard_granularity) >>
> SECTOR_SHIFT;
> when q->limits.discard_granularity is 0 from loop device driver, the
> above calculation returns value 0.
> - Now granularity_aligned_lba and sctor_mapped are 0, req_sectors is
> calculated by the following lines in __blkdev_issue_discard(),
> if (granularity_aligned_lba == sector_mapped)
> req_sects = min_t(sector_t, nr_sects,
> bio_aligned_discard_max_sectors(q));
> because bio_aligned_discard_max_sectors(q) returns 0, req_sects is
> calculated as 0.
> - Now a discard bio is mistakenly initialized as a 0 byte bio by,
> bio->bi_iter.bi_size = req_sects << 9;
> and sent to loop device driver.
> - This discard request is handled by loop device driver by following
> code path,
> loop_handle_cmd => do_req_filebacked => lo_fallocate =>
> file->f_op->fallocate => blkdev_fallocate => blkdev_issue_zeroout =>
> __blkdev_issue_write_zeroes
> - Inside __blkdev_issue_write_zeroes(), a 0 byte length discard bio is
> composed and sent to the backing device of the loop device.
> - In the I/O completion code path, in my case it is,
> blk_done_softirq => nrq->q->mq_ops->complete => nvme_pci_complete_rq
> => nvme_complete_rq => blk_mq_end_request
> inside blk_mq_end_request(), blk_update_request() is called and due to
> req->bio is NULL in previous step, blk_update_request() returns false
> then the BUG() panic in blk_mq_end_request() is triggered.
>
> Although the above panic can be fixed in loop device driver, the generic
> __blkdev_issue_discard() should also be fixed to tolerate the incorrect
> 0 value from queue->limits.discard_granularity, in case some other buggy
> driver makes such mistake again.
>
> This patch checks whether q->limits.discard_granularity is 0 in
> __blkdev_issue_discard() and bio_aligned_discard_max_sectors(). If it is
> 0 from some buggy driver queue, prints a warning oops information and
> set queue_logical_block_size(q) to a local variable discard_granularity.
> This local variable is used in round_up() and round_down() calculation,
> now req_sects won't be 0 and no empty discard request is generated.
>
> Fixes: 9b15d109a6b2 ("block: improve discard bio alignment in __blkdev_issue_discard()")
> Fixes: c52abf563049 ("loop: Better discard support for block devices")
> Reported-by: Ming Lei <[email protected]>
> Signed-off-by: Coly Li <[email protected]>
> Cc: Hannes Reinecke <[email protected]>
> Cc: Ming Lei <[email protected]>
> Cc: Xiao Ni <[email protected]>
> Cc: Bart Van Assche <[email protected]>
> Cc: Christoph Hellwig <[email protected]>
> Cc: Enzo Matsumiya <[email protected]>
> Cc: Jens Axboe <[email protected]>
> Cc: Evan Green <[email protected]>
> ---
> block/blk-lib.c | 8 +++++++-
> block/blk.h | 9 +++++++--
> 2 files changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index 019e09bb9c0e..3017e4cba923 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -30,6 +30,7 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
> struct bio *bio = *biop;
> unsigned int op;
> sector_t bs_mask, part_offset = 0;
> + sector_t discard_granularity;
>
> if (!q)
> return -ENXIO;
> @@ -54,6 +55,11 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
> if (!nr_sects)
> return -EINVAL;
>
> + discard_granularity = q->limits.discard_granularity;
> + /* In case some buggy driver does not set limits.discard_granularity */
> + if (WARN_ON_ONCE(discard_granularity == 0))
> + discard_granularity = queue_logical_block_size(q);
This code path is supposed to not run in case of zero q->limits.discard_granularity,
and looks it is fine to just warn and return -EINVAL in this case,
see Documentation/ABI/testing/sysfs-block:
What: /sys/block/<disk>/queue/discard_granularity
Date: May 2011
Contact: Martin K. Petersen <[email protected]>
Description:
Devices that support discard functionality may
internally allocate space using units that are bigger
than the logical block size. The discard_granularity
parameter indicates the size of the internal allocation
unit in bytes if reported by the device. Otherwise the
discard_granularity will be set to match the device's
physical block size. A discard_granularity of 0 means
that the device does not support discard functionality.
What we need to fix is loop driver, if it claims to support discard,
q->limits.discard_granularity has to be one valid value.
Thanks,
Ming
Ming,
> What we need to fix is loop driver, if it claims to support discard,
> q->limits.discard_granularity has to be one valid value.
Yep!
--
Martin K. Petersen Oracle Linux Engineering
On 2020/8/5 07:58, Ming Lei wrote:
> On Tue, Aug 04, 2020 at 10:23:32PM +0800, Coly Li wrote:
>> When some buggy driver doesn't set its queue->limits.discard_granularity
>> (e.g. current loop device driver), discard at LBA 0 on such device will
>> trigger a kernel BUG() panic from block/blk-mq.c:563.
>>
>> [ 955.565006][ C39] ------------[ cut here ]------------
>> [ 955.559660][ C39] invalid opcode: 0000 [#1] SMP NOPTI
>> [ 955.622171][ C39] CPU: 39 PID: 248 Comm: ksoftirqd/39 Tainted: G E 5.8.0-default+ #40
>> [ 955.622171][ C39] Hardware name: Lenovo ThinkSystem SR650 -[7X05CTO1WW]-/-[7X05CTO1WW]-, BIOS -[IVE160M-2.70]- 07/17/2020
>> [ 955.622175][ C39] RIP: 0010:blk_mq_end_request+0x107/0x110
>> [ 955.622177][ C39] Code: 48 8b 03 e9 59 ff ff ff 48 89 df 5b 5d 41 5c e9 9f ed ff ff 48 8b 35 98 3c f4 00 48 83 c7 10 48 83 c6 19 e8 cb 56 c9 ff eb cb <0f> 0b 0f 1f 80 00 00 00 00 0f 1f 44 00 00 55 48 89 e5 41 56 41 54
>> [ 955.622179][ C39] RSP: 0018:ffffb1288701fe28 EFLAGS: 00010202
>> [ 955.749277][ C39] RAX: 0000000000000001 RBX: ffff956fffba5080 RCX: 0000000000004003
>> [ 955.749278][ C39] RDX: 0000000000000003 RSI: 0000000000000000 RDI: 0000000000000000
>> [ 955.749279][ C39] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
>> [ 955.749279][ C39] R10: ffffb1288701fd28 R11: 0000000000000001 R12: ffffffffa8e05160
>> [ 955.749280][ C39] R13: 0000000000000004 R14: 0000000000000004 R15: ffffffffa7ad3a1e
>> [ 955.749281][ C39] FS: 0000000000000000(0000) GS:ffff95bfbda00000(0000) knlGS:0000000000000000
>> [ 955.749282][ C39] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [ 955.749282][ C39] CR2: 00007f6f0ef766a8 CR3: 0000005a37012002 CR4: 00000000007606e0
>> [ 955.749283][ C39] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> [ 955.749284][ C39] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> [ 955.749284][ C39] PKRU: 55555554
>> [ 955.749285][ C39] Call Trace:
>> [ 955.749290][ C39] blk_done_softirq+0x99/0xc0
>> [ 957.550669][ C39] __do_softirq+0xd3/0x45f
>> [ 957.550677][ C39] ? smpboot_thread_fn+0x2f/0x1e0
>> [ 957.550679][ C39] ? smpboot_thread_fn+0x74/0x1e0
>> [ 957.550680][ C39] ? smpboot_thread_fn+0x14e/0x1e0
>> [ 957.550684][ C39] run_ksoftirqd+0x30/0x60
>> [ 957.550687][ C39] smpboot_thread_fn+0x149/0x1e0
>> [ 957.886225][ C39] ? sort_range+0x20/0x20
>> [ 957.886226][ C39] kthread+0x137/0x160
>> [ 957.886228][ C39] ? kthread_park+0x90/0x90
>> [ 957.886231][ C39] ret_from_fork+0x22/0x30
>> [ 959.117120][ C39] ---[ end trace 3dacdac97e2ed164 ]---
>>
>> This is the procedure to reproduce the panic,
>> # modprobe scsi_debug delay=0 dev_size_mb=2048 max_queue=1
>> # losetup -f /dev/nvme0n1 --direct-io=on
>> # blkdiscard /dev/loop0 -o 0 -l 0x200
>>
>> This is how the BUG() panic triggered by __blkdev_issue_discard(),
>> - For a NVMe SSD backing loop device, the driver does not initialize
>> its queue->limits.discard_granularity and leaves it to 0.
>> - When discard on LBA 0 of the loop device, __blkdev_issue_discard()
>> is called before loop device driver code.
>> - Inside __blkdev_issue_discard(), when calculating value of
>> granularity_aligned_lba by
>> granularity_aligned_lba = round_up(sector_mapped,
>> q->limits.discard_granularity >> SECTOR_SHIFT);
>> because sector_mapped is 0 (at LBA 0 and no partition offset), and
>> q->limits.discard_granularity is 0 (by the buggy loop driver), the
>> calculated granularity_aligned_lba is 0.
>> - The inline function bio_aligned_discard_max_sectors() is defined as
>> return round_down(UINT_MAX, q->limits.discard_granularity) >>
>> SECTOR_SHIFT;
>> when q->limits.discard_granularity is 0 from loop device driver, the
>> above calculation returns value 0.
>> - Now granularity_aligned_lba and sctor_mapped are 0, req_sectors is
>> calculated by the following lines in __blkdev_issue_discard(),
>> if (granularity_aligned_lba == sector_mapped)
>> req_sects = min_t(sector_t, nr_sects,
>> bio_aligned_discard_max_sectors(q));
>> because bio_aligned_discard_max_sectors(q) returns 0, req_sects is
>> calculated as 0.
>> - Now a discard bio is mistakenly initialized as a 0 byte bio by,
>> bio->bi_iter.bi_size = req_sects << 9;
>> and sent to loop device driver.
>> - This discard request is handled by loop device driver by following
>> code path,
>> loop_handle_cmd => do_req_filebacked => lo_fallocate =>
>> file->f_op->fallocate => blkdev_fallocate => blkdev_issue_zeroout =>
>> __blkdev_issue_write_zeroes
>> - Inside __blkdev_issue_write_zeroes(), a 0 byte length discard bio is
>> composed and sent to the backing device of the loop device.
>> - In the I/O completion code path, in my case it is,
>> blk_done_softirq => nrq->q->mq_ops->complete => nvme_pci_complete_rq
>> => nvme_complete_rq => blk_mq_end_request
>> inside blk_mq_end_request(), blk_update_request() is called and due to
>> req->bio is NULL in previous step, blk_update_request() returns false
>> then the BUG() panic in blk_mq_end_request() is triggered.
>>
>> Although the above panic can be fixed in loop device driver, the generic
>> __blkdev_issue_discard() should also be fixed to tolerate the incorrect
>> 0 value from queue->limits.discard_granularity, in case some other buggy
>> driver makes such mistake again.
>>
>> This patch checks whether q->limits.discard_granularity is 0 in
>> __blkdev_issue_discard() and bio_aligned_discard_max_sectors(). If it is
>> 0 from some buggy driver queue, prints a warning oops information and
>> set queue_logical_block_size(q) to a local variable discard_granularity.
>> This local variable is used in round_up() and round_down() calculation,
>> now req_sects won't be 0 and no empty discard request is generated.
>>
>> Fixes: 9b15d109a6b2 ("block: improve discard bio alignment in __blkdev_issue_discard()")
>> Fixes: c52abf563049 ("loop: Better discard support for block devices")
>> Reported-by: Ming Lei <[email protected]>
>> Signed-off-by: Coly Li <[email protected]>
>> Cc: Hannes Reinecke <[email protected]>
>> Cc: Ming Lei <[email protected]>
>> Cc: Xiao Ni <[email protected]>
>> Cc: Bart Van Assche <[email protected]>
>> Cc: Christoph Hellwig <[email protected]>
>> Cc: Enzo Matsumiya <[email protected]>
>> Cc: Jens Axboe <[email protected]>
>> Cc: Evan Green <[email protected]>
>> ---
>> block/blk-lib.c | 8 +++++++-
>> block/blk.h | 9 +++++++--
>> 2 files changed, 14 insertions(+), 3 deletions(-)
>>
>> diff --git a/block/blk-lib.c b/block/blk-lib.c
>> index 019e09bb9c0e..3017e4cba923 100644
>> --- a/block/blk-lib.c
>> +++ b/block/blk-lib.c
>> @@ -30,6 +30,7 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
>> struct bio *bio = *biop;
>> unsigned int op;
>> sector_t bs_mask, part_offset = 0;
>> + sector_t discard_granularity;
>>
>> if (!q)
>> return -ENXIO;
>> @@ -54,6 +55,11 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
>> if (!nr_sects)
>> return -EINVAL;
>>
>> + discard_granularity = q->limits.discard_granularity;
>> + /* In case some buggy driver does not set limits.discard_granularity */
>> + if (WARN_ON_ONCE(discard_granularity == 0))
>> + discard_granularity = queue_logical_block_size(q);
>
> This code path is supposed to not run in case of zero q->limits.discard_granularity,
> and looks it is fine to just warn and return -EINVAL in this case,
> see Documentation/ABI/testing/sysfs-block:
>
> What: /sys/block/<disk>/queue/discard_granularity
> Date: May 2011
> Contact: Martin K. Petersen <[email protected]>
> Description:
> Devices that support discard functionality may
> internally allocate space using units that are bigger
> than the logical block size. The discard_granularity
> parameter indicates the size of the internal allocation
> unit in bytes if reported by the device. Otherwise the
> discard_granularity will be set to match the device's
> physical block size. A discard_granularity of 0 means
> that the device does not support discard functionality.
>
> What we need to fix is loop driver, if it claims to support discard,
> q->limits.discard_granularity has to be one valid value.
Yes your suggestion is much simpler, let me do it :-)
Thanks.
Coly Li
On Wed, Aug 05, 2020 at 09:54:00AM +0800, Coly Li wrote:
> On 2020/8/5 07:58, Ming Lei wrote:
> > On Tue, Aug 04, 2020 at 10:23:32PM +0800, Coly Li wrote:
> >> When some buggy driver doesn't set its queue->limits.discard_granularity
> >> (e.g. current loop device driver), discard at LBA 0 on such device will
> >> trigger a kernel BUG() panic from block/blk-mq.c:563.
> >>
> >> [ 955.565006][ C39] ------------[ cut here ]------------
> >> [ 955.559660][ C39] invalid opcode: 0000 [#1] SMP NOPTI
> >> [ 955.622171][ C39] CPU: 39 PID: 248 Comm: ksoftirqd/39 Tainted: G E 5.8.0-default+ #40
> >> [ 955.622171][ C39] Hardware name: Lenovo ThinkSystem SR650 -[7X05CTO1WW]-/-[7X05CTO1WW]-, BIOS -[IVE160M-2.70]- 07/17/2020
> >> [ 955.622175][ C39] RIP: 0010:blk_mq_end_request+0x107/0x110
> >> [ 955.622177][ C39] Code: 48 8b 03 e9 59 ff ff ff 48 89 df 5b 5d 41 5c e9 9f ed ff ff 48 8b 35 98 3c f4 00 48 83 c7 10 48 83 c6 19 e8 cb 56 c9 ff eb cb <0f> 0b 0f 1f 80 00 00 00 00 0f 1f 44 00 00 55 48 89 e5 41 56 41 54
> >> [ 955.622179][ C39] RSP: 0018:ffffb1288701fe28 EFLAGS: 00010202
> >> [ 955.749277][ C39] RAX: 0000000000000001 RBX: ffff956fffba5080 RCX: 0000000000004003
> >> [ 955.749278][ C39] RDX: 0000000000000003 RSI: 0000000000000000 RDI: 0000000000000000
> >> [ 955.749279][ C39] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> >> [ 955.749279][ C39] R10: ffffb1288701fd28 R11: 0000000000000001 R12: ffffffffa8e05160
> >> [ 955.749280][ C39] R13: 0000000000000004 R14: 0000000000000004 R15: ffffffffa7ad3a1e
> >> [ 955.749281][ C39] FS: 0000000000000000(0000) GS:ffff95bfbda00000(0000) knlGS:0000000000000000
> >> [ 955.749282][ C39] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> [ 955.749282][ C39] CR2: 00007f6f0ef766a8 CR3: 0000005a37012002 CR4: 00000000007606e0
> >> [ 955.749283][ C39] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> >> [ 955.749284][ C39] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> >> [ 955.749284][ C39] PKRU: 55555554
> >> [ 955.749285][ C39] Call Trace:
> >> [ 955.749290][ C39] blk_done_softirq+0x99/0xc0
> >> [ 957.550669][ C39] __do_softirq+0xd3/0x45f
> >> [ 957.550677][ C39] ? smpboot_thread_fn+0x2f/0x1e0
> >> [ 957.550679][ C39] ? smpboot_thread_fn+0x74/0x1e0
> >> [ 957.550680][ C39] ? smpboot_thread_fn+0x14e/0x1e0
> >> [ 957.550684][ C39] run_ksoftirqd+0x30/0x60
> >> [ 957.550687][ C39] smpboot_thread_fn+0x149/0x1e0
> >> [ 957.886225][ C39] ? sort_range+0x20/0x20
> >> [ 957.886226][ C39] kthread+0x137/0x160
> >> [ 957.886228][ C39] ? kthread_park+0x90/0x90
> >> [ 957.886231][ C39] ret_from_fork+0x22/0x30
> >> [ 959.117120][ C39] ---[ end trace 3dacdac97e2ed164 ]---
> >>
> >> This is the procedure to reproduce the panic,
> >> # modprobe scsi_debug delay=0 dev_size_mb=2048 max_queue=1
> >> # losetup -f /dev/nvme0n1 --direct-io=on
> >> # blkdiscard /dev/loop0 -o 0 -l 0x200
> >>
> >> This is how the BUG() panic triggered by __blkdev_issue_discard(),
> >> - For a NVMe SSD backing loop device, the driver does not initialize
> >> its queue->limits.discard_granularity and leaves it to 0.
> >> - When discard on LBA 0 of the loop device, __blkdev_issue_discard()
> >> is called before loop device driver code.
> >> - Inside __blkdev_issue_discard(), when calculating value of
> >> granularity_aligned_lba by
> >> granularity_aligned_lba = round_up(sector_mapped,
> >> q->limits.discard_granularity >> SECTOR_SHIFT);
> >> because sector_mapped is 0 (at LBA 0 and no partition offset), and
> >> q->limits.discard_granularity is 0 (by the buggy loop driver), the
> >> calculated granularity_aligned_lba is 0.
> >> - The inline function bio_aligned_discard_max_sectors() is defined as
> >> return round_down(UINT_MAX, q->limits.discard_granularity) >>
> >> SECTOR_SHIFT;
> >> when q->limits.discard_granularity is 0 from loop device driver, the
> >> above calculation returns value 0.
> >> - Now granularity_aligned_lba and sctor_mapped are 0, req_sectors is
> >> calculated by the following lines in __blkdev_issue_discard(),
> >> if (granularity_aligned_lba == sector_mapped)
> >> req_sects = min_t(sector_t, nr_sects,
> >> bio_aligned_discard_max_sectors(q));
> >> because bio_aligned_discard_max_sectors(q) returns 0, req_sects is
> >> calculated as 0.
> >> - Now a discard bio is mistakenly initialized as a 0 byte bio by,
> >> bio->bi_iter.bi_size = req_sects << 9;
> >> and sent to loop device driver.
> >> - This discard request is handled by loop device driver by following
> >> code path,
> >> loop_handle_cmd => do_req_filebacked => lo_fallocate =>
> >> file->f_op->fallocate => blkdev_fallocate => blkdev_issue_zeroout =>
> >> __blkdev_issue_write_zeroes
> >> - Inside __blkdev_issue_write_zeroes(), a 0 byte length discard bio is
> >> composed and sent to the backing device of the loop device.
> >> - In the I/O completion code path, in my case it is,
> >> blk_done_softirq => nrq->q->mq_ops->complete => nvme_pci_complete_rq
> >> => nvme_complete_rq => blk_mq_end_request
> >> inside blk_mq_end_request(), blk_update_request() is called and due to
> >> req->bio is NULL in previous step, blk_update_request() returns false
> >> then the BUG() panic in blk_mq_end_request() is triggered.
> >>
> >> Although the above panic can be fixed in loop device driver, the generic
> >> __blkdev_issue_discard() should also be fixed to tolerate the incorrect
> >> 0 value from queue->limits.discard_granularity, in case some other buggy
> >> driver makes such mistake again.
> >>
> >> This patch checks whether q->limits.discard_granularity is 0 in
> >> __blkdev_issue_discard() and bio_aligned_discard_max_sectors(). If it is
> >> 0 from some buggy driver queue, prints a warning oops information and
> >> set queue_logical_block_size(q) to a local variable discard_granularity.
> >> This local variable is used in round_up() and round_down() calculation,
> >> now req_sects won't be 0 and no empty discard request is generated.
> >>
> >> Fixes: 9b15d109a6b2 ("block: improve discard bio alignment in __blkdev_issue_discard()")
> >> Fixes: c52abf563049 ("loop: Better discard support for block devices")
> >> Reported-by: Ming Lei <[email protected]>
> >> Signed-off-by: Coly Li <[email protected]>
> >> Cc: Hannes Reinecke <[email protected]>
> >> Cc: Ming Lei <[email protected]>
> >> Cc: Xiao Ni <[email protected]>
> >> Cc: Bart Van Assche <[email protected]>
> >> Cc: Christoph Hellwig <[email protected]>
> >> Cc: Enzo Matsumiya <[email protected]>
> >> Cc: Jens Axboe <[email protected]>
> >> Cc: Evan Green <[email protected]>
> >> ---
> >> block/blk-lib.c | 8 +++++++-
> >> block/blk.h | 9 +++++++--
> >> 2 files changed, 14 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/block/blk-lib.c b/block/blk-lib.c
> >> index 019e09bb9c0e..3017e4cba923 100644
> >> --- a/block/blk-lib.c
> >> +++ b/block/blk-lib.c
> >> @@ -30,6 +30,7 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
> >> struct bio *bio = *biop;
> >> unsigned int op;
> >> sector_t bs_mask, part_offset = 0;
> >> + sector_t discard_granularity;
> >>
> >> if (!q)
> >> return -ENXIO;
> >> @@ -54,6 +55,11 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
> >> if (!nr_sects)
> >> return -EINVAL;
> >>
> >> + discard_granularity = q->limits.discard_granularity;
> >> + /* In case some buggy driver does not set limits.discard_granularity */
> >> + if (WARN_ON_ONCE(discard_granularity == 0))
> >> + discard_granularity = queue_logical_block_size(q);
> >
> > This code path is supposed to not run in case of zero q->limits.discard_granularity,
> > and looks it is fine to just warn and return -EINVAL in this case,
> > see Documentation/ABI/testing/sysfs-block:
> >
> > What: /sys/block/<disk>/queue/discard_granularity
> > Date: May 2011
> > Contact: Martin K. Petersen <[email protected]>
> > Description:
> > Devices that support discard functionality may
> > internally allocate space using units that are bigger
> > than the logical block size. The discard_granularity
> > parameter indicates the size of the internal allocation
> > unit in bytes if reported by the device. Otherwise the
> > discard_granularity will be set to match the device's
> > physical block size. A discard_granularity of 0 means
> > that the device does not support discard functionality.
> >
> > What we need to fix is loop driver, if it claims to support discard,
> > q->limits.discard_granularity has to be one valid value.
>
> Yes your suggestion is much simpler, let me do it :-)
That is exactly what the following patch does:
https://lore.kernel.org/linux-block/[email protected]/T/#m82a878277ae7ed6b7a595820112fd13beaa24c99
Thanks,
Ming
On 2020/8/5 10:46, Ming Lei wrote:
> On Wed, Aug 05, 2020 at 09:54:00AM +0800, Coly Li wrote:
>> On 2020/8/5 07:58, Ming Lei wrote:
>>> On Tue, Aug 04, 2020 at 10:23:32PM +0800, Coly Li wrote:
>>>> When some buggy driver doesn't set its queue->limits.discard_granularity
>>>> (e.g. current loop device driver), discard at LBA 0 on such device will
>>>> trigger a kernel BUG() panic from block/blk-mq.c:563.
>>>>
>>>> [ 955.565006][ C39] ------------[ cut here ]------------
>>>> [ 955.559660][ C39] invalid opcode: 0000 [#1] SMP NOPTI
>>>> [ 955.622171][ C39] CPU: 39 PID: 248 Comm: ksoftirqd/39 Tainted: G E 5.8.0-default+ #40
>>>> [ 955.622171][ C39] Hardware name: Lenovo ThinkSystem SR650 -[7X05CTO1WW]-/-[7X05CTO1WW]-, BIOS -[IVE160M-2.70]- 07/17/2020
>>>> [ 955.622175][ C39] RIP: 0010:blk_mq_end_request+0x107/0x110
>>>> [ 955.622177][ C39] Code: 48 8b 03 e9 59 ff ff ff 48 89 df 5b 5d 41 5c e9 9f ed ff ff 48 8b 35 98 3c f4 00 48 83 c7 10 48 83 c6 19 e8 cb 56 c9 ff eb cb <0f> 0b 0f 1f 80 00 00 00 00 0f 1f 44 00 00 55 48 89 e5 41 56 41 54
>>>> [ 955.622179][ C39] RSP: 0018:ffffb1288701fe28 EFLAGS: 00010202
>>>> [ 955.749277][ C39] RAX: 0000000000000001 RBX: ffff956fffba5080 RCX: 0000000000004003
>>>> [ 955.749278][ C39] RDX: 0000000000000003 RSI: 0000000000000000 RDI: 0000000000000000
>>>> [ 955.749279][ C39] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
>>>> [ 955.749279][ C39] R10: ffffb1288701fd28 R11: 0000000000000001 R12: ffffffffa8e05160
>>>> [ 955.749280][ C39] R13: 0000000000000004 R14: 0000000000000004 R15: ffffffffa7ad3a1e
>>>> [ 955.749281][ C39] FS: 0000000000000000(0000) GS:ffff95bfbda00000(0000) knlGS:0000000000000000
>>>> [ 955.749282][ C39] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>> [ 955.749282][ C39] CR2: 00007f6f0ef766a8 CR3: 0000005a37012002 CR4: 00000000007606e0
>>>> [ 955.749283][ C39] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>>> [ 955.749284][ C39] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>>> [ 955.749284][ C39] PKRU: 55555554
>>>> [ 955.749285][ C39] Call Trace:
>>>> [ 955.749290][ C39] blk_done_softirq+0x99/0xc0
>>>> [ 957.550669][ C39] __do_softirq+0xd3/0x45f
>>>> [ 957.550677][ C39] ? smpboot_thread_fn+0x2f/0x1e0
>>>> [ 957.550679][ C39] ? smpboot_thread_fn+0x74/0x1e0
>>>> [ 957.550680][ C39] ? smpboot_thread_fn+0x14e/0x1e0
>>>> [ 957.550684][ C39] run_ksoftirqd+0x30/0x60
>>>> [ 957.550687][ C39] smpboot_thread_fn+0x149/0x1e0
>>>> [ 957.886225][ C39] ? sort_range+0x20/0x20
>>>> [ 957.886226][ C39] kthread+0x137/0x160
>>>> [ 957.886228][ C39] ? kthread_park+0x90/0x90
>>>> [ 957.886231][ C39] ret_from_fork+0x22/0x30
>>>> [ 959.117120][ C39] ---[ end trace 3dacdac97e2ed164 ]---
>>>>
>>>> This is the procedure to reproduce the panic,
>>>> # modprobe scsi_debug delay=0 dev_size_mb=2048 max_queue=1
>>>> # losetup -f /dev/nvme0n1 --direct-io=on
>>>> # blkdiscard /dev/loop0 -o 0 -l 0x200
>>>>
>>>> This is how the BUG() panic triggered by __blkdev_issue_discard(),
>>>> - For a NVMe SSD backing loop device, the driver does not initialize
>>>> its queue->limits.discard_granularity and leaves it to 0.
>>>> - When discard on LBA 0 of the loop device, __blkdev_issue_discard()
>>>> is called before loop device driver code.
>>>> - Inside __blkdev_issue_discard(), when calculating value of
>>>> granularity_aligned_lba by
>>>> granularity_aligned_lba = round_up(sector_mapped,
>>>> q->limits.discard_granularity >> SECTOR_SHIFT);
>>>> because sector_mapped is 0 (at LBA 0 and no partition offset), and
>>>> q->limits.discard_granularity is 0 (by the buggy loop driver), the
>>>> calculated granularity_aligned_lba is 0.
>>>> - The inline function bio_aligned_discard_max_sectors() is defined as
>>>> return round_down(UINT_MAX, q->limits.discard_granularity) >>
>>>> SECTOR_SHIFT;
>>>> when q->limits.discard_granularity is 0 from loop device driver, the
>>>> above calculation returns value 0.
>>>> - Now granularity_aligned_lba and sctor_mapped are 0, req_sectors is
>>>> calculated by the following lines in __blkdev_issue_discard(),
>>>> if (granularity_aligned_lba == sector_mapped)
>>>> req_sects = min_t(sector_t, nr_sects,
>>>> bio_aligned_discard_max_sectors(q));
>>>> because bio_aligned_discard_max_sectors(q) returns 0, req_sects is
>>>> calculated as 0.
>>>> - Now a discard bio is mistakenly initialized as a 0 byte bio by,
>>>> bio->bi_iter.bi_size = req_sects << 9;
>>>> and sent to loop device driver.
>>>> - This discard request is handled by loop device driver by following
>>>> code path,
>>>> loop_handle_cmd => do_req_filebacked => lo_fallocate =>
>>>> file->f_op->fallocate => blkdev_fallocate => blkdev_issue_zeroout =>
>>>> __blkdev_issue_write_zeroes
>>>> - Inside __blkdev_issue_write_zeroes(), a 0 byte length discard bio is
>>>> composed and sent to the backing device of the loop device.
>>>> - In the I/O completion code path, in my case it is,
>>>> blk_done_softirq => nrq->q->mq_ops->complete => nvme_pci_complete_rq
>>>> => nvme_complete_rq => blk_mq_end_request
>>>> inside blk_mq_end_request(), blk_update_request() is called and due to
>>>> req->bio is NULL in previous step, blk_update_request() returns false
>>>> then the BUG() panic in blk_mq_end_request() is triggered.
>>>>
>>>> Although the above panic can be fixed in loop device driver, the generic
>>>> __blkdev_issue_discard() should also be fixed to tolerate the incorrect
>>>> 0 value from queue->limits.discard_granularity, in case some other buggy
>>>> driver makes such mistake again.
>>>>
>>>> This patch checks whether q->limits.discard_granularity is 0 in
>>>> __blkdev_issue_discard() and bio_aligned_discard_max_sectors(). If it is
>>>> 0 from some buggy driver queue, prints a warning oops information and
>>>> set queue_logical_block_size(q) to a local variable discard_granularity.
>>>> This local variable is used in round_up() and round_down() calculation,
>>>> now req_sects won't be 0 and no empty discard request is generated.
>>>>
>>>> Fixes: 9b15d109a6b2 ("block: improve discard bio alignment in __blkdev_issue_discard()")
>>>> Fixes: c52abf563049 ("loop: Better discard support for block devices")
>>>> Reported-by: Ming Lei <[email protected]>
>>>> Signed-off-by: Coly Li <[email protected]>
>>>> Cc: Hannes Reinecke <[email protected]>
>>>> Cc: Ming Lei <[email protected]>
>>>> Cc: Xiao Ni <[email protected]>
>>>> Cc: Bart Van Assche <[email protected]>
>>>> Cc: Christoph Hellwig <[email protected]>
>>>> Cc: Enzo Matsumiya <[email protected]>
>>>> Cc: Jens Axboe <[email protected]>
>>>> Cc: Evan Green <[email protected]>
>>>> ---
>>>> block/blk-lib.c | 8 +++++++-
>>>> block/blk.h | 9 +++++++--
>>>> 2 files changed, 14 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/block/blk-lib.c b/block/blk-lib.c
>>>> index 019e09bb9c0e..3017e4cba923 100644
>>>> --- a/block/blk-lib.c
>>>> +++ b/block/blk-lib.c
>>>> @@ -30,6 +30,7 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
>>>> struct bio *bio = *biop;
>>>> unsigned int op;
>>>> sector_t bs_mask, part_offset = 0;
>>>> + sector_t discard_granularity;
>>>>
>>>> if (!q)
>>>> return -ENXIO;
>>>> @@ -54,6 +55,11 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
>>>> if (!nr_sects)
>>>> return -EINVAL;
>>>>
>>>> + discard_granularity = q->limits.discard_granularity;
>>>> + /* In case some buggy driver does not set limits.discard_granularity */
>>>> + if (WARN_ON_ONCE(discard_granularity == 0))
>>>> + discard_granularity = queue_logical_block_size(q);
>>>
>>> This code path is supposed to not run in case of zero q->limits.discard_granularity,
>>> and looks it is fine to just warn and return -EINVAL in this case,
>>> see Documentation/ABI/testing/sysfs-block:
>>>
>>> What: /sys/block/<disk>/queue/discard_granularity
>>> Date: May 2011
>>> Contact: Martin K. Petersen <[email protected]>
>>> Description:
>>> Devices that support discard functionality may
>>> internally allocate space using units that are bigger
>>> than the logical block size. The discard_granularity
>>> parameter indicates the size of the internal allocation
>>> unit in bytes if reported by the device. Otherwise the
>>> discard_granularity will be set to match the device's
>>> physical block size. A discard_granularity of 0 means
>>> that the device does not support discard functionality.
>>>
>>> What we need to fix is loop driver, if it claims to support discard,
>>> q->limits.discard_granularity has to be one valid value.
>>
>> Yes your suggestion is much simpler, let me do it :-)
>
> That is exactly what the following patch does:
>
> https://lore.kernel.org/linux-block/[email protected]/T/#m82a878277ae7ed6b7a595820112fd13beaa24c99
I meant your suggestion in __blkdev_issue_discard(), in case some other
buggy driver does similar fault in future. Now the v2 patch is much
simpler, please review it and thank you in advance :-)
Coly Li