[GEDI] [PATCH v2 01/17] block/throttle-groups: throttle_group_co_io_limits_intercept(): 64bit bytes

Eric Blake eblake at redhat.com
Tue Apr 28 22:09:38 UTC 2020

On 4/27/20 3:23 AM, Vladimir Sementsov-Ogievskiy wrote:
> The function is called from 64bit io handlers, and bytes is just passed
> to throttle_account() which is 64bit too (unsigned though). So, let's
> convert intermediate argument to 64bit too.

My audit for this patch:

Caller has 32-bit, this patch now causes widening which is safe:
block/block-backend.c: blk_do_preadv() passes 'unsigned int'
block/block-backend.c: blk_do_pwritev_part() passes 'unsigned int'
block/throttle.c: throttle_co_pwrite_zeroes() passes 'int'
block/throttle.c: throttle_co_pdiscard() passes 'int'

Caller has 64-bit, this patch fixes potential bug where pre-patch could 
narrow, except it's easy enough to trace that callers are still capped 
at 2G actions:
block/throttle.c: throttle_co_preadv() passes 'uint64_t'
block/throttle.c: throttle_co_pwritev() passes 'uint64_t'

Implementation in question: block/throttle-groups.c 
throttle_group_co_io_limits_intercept() takes 'unsigned int bytes' and 
uses it:
argument to util/throttle.c throttle_account(uint64_t)

All safe: it patches a latent bug, and does not introduce any 64-bit 
gotchas once throttle_co_p{read,write}v are relaxed, and assuming 
throttle_account() is not buggy.

> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov at virtuozzo.com>
> ---
>   include/block/throttle-groups.h | 2 +-
>   block/throttle-groups.c         | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)

Reviewed-by: Eric Blake <eblake at redhat.com>

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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