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"?


>> [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

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