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.