Bart, On 4/5/18 00:22, Bart Van Assche wrote: > On Wed, 2018-04-04 at 17:54 +0900, Damien Le Moal wrote: >> Since SCSI scanning occurs asynchronously, since sd_revalidate_disk() >> is called from sd_probe_async() and since sd_revalidate_disk() calls >> sd_zbc_read_zones() it can happen that sd_zbc_read_zones() is called >> concurrently with operations referencing a drive zone bitmaps and number > ^^^^^^^^^^^^^^^^^^^^ > > Should "a" be changed into "the"? Yes. >> [Damien] Updated commit message and changed nr_zones/bitmap swap order. > > Updating the number of zones after having updated the bitmap pointers is not > sufficient to avoid trouble if the number of zones as reported by the drive > changes while I/O is in progress. With the current implementation if the > number of zones changes the seq_zones_bitmap is cleared. Can this cause > trouble for the mq-deadline scheduler? Additionally, CPUs other than x86 can > reorder store operations. Even worse, a CPU could cache the zone bitmap > pointers which means that at least RCU protection + kfree_rcu() is needed to > avoid trouble. I think we either should handle this case properly or issue a > kernel warning. OK. Let's work on that. -- Damien Le Moal, Western Digital
