Re: [PATCH] dm-log-writes: fix bug with too large bios

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On 05/27/2016 10:51 AM, Mikulas Patocka wrote:
bio_alloc can allocate a bio with at most BIO_MAX_PAGES (256) vector
entries. However, the incoming bio may have more vector entries if it was
allocated by other means. For example, bcache submits bios with more than
BIO_MAX_PAGES entries. This results in bio_alloc failure.

To avoid the failure, change the code so that it allocates bio with at
most BIO_MAX_PAGES entries. If the incoming bio has more entries,
bio_add_page will fail and a new bio will be allocated - the code that
handles bio_add_page failure already exists in the dm-log-writes target.

Also, move atomic_inc(&lc->io_blocks) before bio_alloc to fix a bug that
the target hangs if bio_alloc fails. The error path does put_io_block(lc),
so we must do atomic_inc(&lc->io_blocks) before invoking the error path to
avoid underflow of lc->io_blocks.

Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx	# v4.1+

Reviewed-by: Josef Bacik <jbacik@xxxxxx>

Thanks,

Josef

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