Messages in this thread | | | Subject | Re: dm-bufio: adjust the reserved buffer for dm-verify-target. | From | "Xiao, Jin" <> | Date | Thu, 16 Aug 2018 09:32:43 +0800 |
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On 8/15/2018 4:32 AM, Mike Snitzer wrote: > On Wed, Aug 08 2018 at 2:40am -0400, > xiao jin <jin.xiao@intel.com> wrote: > >> We hit the BUG() report at include/linux/scatterlist.h:144! >> The callback is as bellow: >> => verity_work >> => verity_hash_for_block >> => verity_verify_level >> => verity_hash >> => verity_hash_update >> => sg_init_one >> => sg_set_buf >> >> More debug shows the root cause. When creating dufio client it >> uses the __vmalloc() to allocate the buffer data for the reserved >> dm_buffer. The buffer that allocated by the __vmalloc() is invalid >> according to the __virt_addr_valid(). >> >> Mostly the reserved dm_buffer is not touched. But occasionally >> it might fail to allocate the dm_buffer data when we try to >> allocate in the __alloc_buffer_wait_no_callback(). Then it has >> to take the reserved dm_buffer for usage. Finally it reports the >> BUG() as virt_addr_valid() detects the buffer data address is invalid. >> >> The patch is to adjust the reserved buffer for dm-verity-target. We >> allocated two dm_buffers into the reserved buffers list when creating >> the buffer interface. The first dm_buffer in the reserved buffer list >> is allocated by the __vmalloc(), it's not used after that. The second >> dm_buffer in the reserved buffer list is allocated by the >> __get_free_pages() which can be consumed after that. >> >> Signed-off-by: xiao jin <jin.xiao@intel.com> >> --- >> drivers/md/dm-bufio.c | 4 ++-- >> drivers/md/dm-verity-target.c | 2 +- >> 2 files changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c >> index dc385b7..3b7ca5e 100644 >> --- a/drivers/md/dm-bufio.c >> +++ b/drivers/md/dm-bufio.c >> @@ -841,7 +841,7 @@ static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client >> tried_noio_alloc = true; >> } >> >> - if (!list_empty(&c->reserved_buffers)) { >> + if (!c->need_reserved_buffers) { >> b = list_entry(c->reserved_buffers.next, >> struct dm_buffer, lru_list); >> list_del(&b->lru_list); >> @@ -1701,7 +1701,7 @@ struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsign >> goto bad; >> } >> >> - while (c->need_reserved_buffers) { >> + if (list_empty(&c->reserved_buffers)) { >> struct dm_buffer *b = alloc_buffer(c, GFP_KERNEL); >> >> if (!b) { > Point was to allocate N buffers (as accounted in > c->need_reserved_buffers). This change just allocates a single one. > Why? > > Your header isn't clear on this at all.
Hi Mike,
Currently alloc_buffer() when creating the client will use the __vmalloc() to
get the buffer data for c->reserved_buffers. If the c->reserved_buffers is read to
use in the failures case of buffer allocation in the __alloc_buffer_wait_no_callback(),
and the CONFIG_DEBUG_SG is enabled, we will hit the BUG() report.
That's the problem I find in reality.
I have some thinking to solve such issue. I think to keep the initial buffer with the
data from __vmalloc() in the c->reserved_buffers. But the reserved buffer with the data
from __vmalloc() can't be read to use. We can allocate more buffers with the
data mode of DATA_MODE_SLAB or DATA_MODE_GET_FREE_PAGES for c->reserved_buffers.
Such reserved buffers can be used in the failures case of buffer allocation
in the __alloc_buffer_wait_no_callback().
I test the code on my device. I never see the BUG() report again. Feel free to correct me.
Thanks.
Jin
>> diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c >> index 12decdbd7..40c66fc 100644 >> --- a/drivers/md/dm-verity-target.c >> +++ b/drivers/md/dm-verity-target.c >> @@ -1107,7 +1107,7 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv) >> v->hash_blocks = hash_position; >> >> v->bufio = dm_bufio_client_create(v->hash_dev->bdev, >> - 1 << v->hash_dev_block_bits, 1, sizeof(struct buffer_aux), >> + 1 << v->hash_dev_block_bits, 2, sizeof(struct buffer_aux), >> dm_bufio_alloc_callback, NULL); >> if (IS_ERR(v->bufio)) { >> ti->error = "Cannot initialize dm-bufio"; >> -- >> 2.7.4 >> >> -- >> dm-devel mailing list >> dm-devel@redhat.com >> https://www.redhat.com/mailman/listinfo/dm-devel > It isn't at all clear from my initial review that what you're doing > makes any sense. > > Seems like you're just papering over bufio's use of !__virt_addr_valid() > memory in unintuitive ways. > > Mikulas, can you see a better way forward? > > Mike
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