On Wed, Nov 22, 2023 at 04:19:40PM +0800, Ming Lei wrote: > On Tue, Nov 21, 2023 at 11:53:17PM -0800, Christoph Hellwig wrote: > > On Wed, Nov 22, 2023 at 03:45:24PM +0800, Ming Lei wrote: > > > All the existed 'bool' flags are not atomic RW, so I think it isn't > > > necessary to define 'bd_flags' as 'unsigned long' for replacing them. > > > > So because the old code wasn't correct we'll never bother? The new > > flag and the new placement certainly make this more critical as well. > > Can you explain why the old code was wrong? > > 1) ->bd_read_only and ->bd_make_it_fail > > - set from userspace interface(ioctl or sysfs) > - check in IO code path > > so changing it into atomic bit doesn't make difference from user > viewpoint. > > 2) ->bd_write_holder > > disk->open_mutex is held for read & write this flag > > 3) ->bd_has_submit_bio > > This flag is setup as oneshot before adding disk, and check in FS io code > path. On architectures that can't do byte-level atomics all three can corrupt each other, and even worse bd_partno. Granted that is only alpha these days IIRC, but it's still buggy.
