On Fri, Jul 14, 2017 at 08:22:31AM -0600, Jens Axboe wrote:
> /*
> * drivers should _never_ use the all version - the bio may have been split
> - * before it got to the driver and the driver won't own all of it
> + * before it got to the driver and the driver won't own all of it.
> + *
> + * Don't use this on cloned bio's.
> */
> #define bio_for_each_segment_all(bvl, bio, i) \
> + WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)); \
> for (i = 0, bvl = (bio)->bi_io_vec; i < (bio)->bi_vcnt; i++, bvl++)
This needs a multiline statement protection, otherwise
if (...)
bio_for_each_segment_all(...) {
...
}
would expand to
if (...)
WARN_ON_ONCE(...);
bio_for_each_segment_all(...) { ... }
However "do { ... } while(0)" cannot be used here, so WARN_ON_ONCE could
be moved to the initialization block of for:
#define bio_for_each_segment_all(bvl, bio, i) \
for (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)), \
i = 0, bvl = (bio)->bi_io_vec; i < (bio)->bi_vcnt; i++, bvl++)
I haven't found any code using the exact broken pattern. So this does
not explain the crash Liu Bo reports.
