Re: [PATCH v3] scsi: core: Fix async_scan race condition with READ_ONCE/WRITE_ONCE

[Chaohai Chen]

On Wed, Mar 04, 2026 at 09:20:25AM +0000, John Garry wrote:
> On 04/03/2026 07:57, Chaohai Chen wrote:
> > Previously, host_lock was used to prevent bit-set conflicts in async_scan,
> > but this approach introduced naked reads in some code paths.
> > 
> > Convert async_scan from a bitfield to a bool type to eliminate bit-level
> > conflicts entirely. Use READ_ONCE() and WRITE_ONCE() to ensure proper
> > memory ordering on Alpha and satisfy KCSAN requirements.
> 
> Is the shost->scan_mutex always held when shost->async_scan is read/written?
> 
Yes. In theory, there is no need for READ-ONCE/WRITE-ONCE. Plus, this belongs 
to defensive programming. And it indicates that this is a shared variable, 
which means that this variable will be accessed by multiple threads and 
concurrency issues need to be handled carefully.