Re: [PATCH] slab: distinguish lock and trylock for sheaf_flush_main()

["Vlastimil Babka (SUSE)" <vbabka@kernel.org>]

On 2/26/26 15:50, Vlastimil Babka (SUSE) wrote:
> On 2/11/26 10:42, Vlastimil Babka wrote:
>> sheaf_flush_main() can be called from __pcs_replace_full_main() where
>> the trylock can in theory fail, and pcs_flush_all() where it's not
>> expected to and it would be actually a problem if it failed and left the
>> main sheaf not flushed.
> 
> Thinking about this more, I now think it's not a theoretical issue because
> on PREEMPT_RT I think pcs_flush_all() can preempt someone holding the lock
> (on PREEMPT_RT it doesn't have to be an irq handler preempting a holder),
> and then fail to flush the main sheaf silently.
> 
> The impact is probably limited though - if this failure to flush happens in
> __kmem_cache_shutdown(), it means someone was destroying a cache while using
> it, so that was already buggy. slab_mem_going_offline_callback() could be
> where this matters although it's unlikely someone would do memory hotplug
> together with PREEMPT_RT.
> 
> But maybe still worth tagging this as Fixes: 2d517aa09bbc ("slab: add opt-in
> caching layer of percpu sheaves") and Cc stable and sending it as a hotfix.

Added to slab/for-next-fixes with adjusted changelog:

https://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab.git/commit/?h=slab/for-next-fixes&id=48647d3f9a644d1e81af6558102d43cdb260597b