On 30/09/20 16:31, Maxim Levitsky wrote: >> + >> + qatomic_set(&dev->realized, value); >> + /* >> + * Ensure that concurrent users see this update prior to >> + * any other changes done by unrealize. >> + */ >> + smp_wmb(); > > I''l probably never fully understand where to use read/write/full barrier. > If I understand corrctly, read barrier prevents reads done by this thread to > be reordered, > by the CPU and write barrier prevents writes done by this CPU to be > re-ordered.
I must say that the above is not really satisfactory. The right thing to do would be to say which changes are done by unrealize; then you should make sure that *after* reading something that unrealize could undo you check if dev->realized is still true. scsi_device_find is one such case, but I'm not convinced it is enough. Paolo > Both (depending on the macro) usually imply compiler barrier (to avoid > compilier re-ordering > stuff...)
