On Mon, Oct 10, 2022 at 10:45:43PM +0200, Vlastimil Babka wrote: > On 10/10/22 16:22, Mel Gorman wrote: > > On Wed, Aug 24, 2022 at 10:58:26PM -0600, Yu Zhao wrote: > > > On Wed, Aug 24, 2022 at 8:18 AM Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > The pcp_spin_lock_irqsave protecting the PCP lists is IRQ-safe as a task > > > > allocating from the PCP must not re-enter the allocator from IRQ context. > > > > In each instance where IRQ-reentrancy is possible, the lock is acquired using > > > > pcp_spin_trylock_irqsave() even though IRQs are disabled and re-entrancy > > > > is impossible. > > > > > > > > Demote the lock to pcp_spin_lock avoids an IRQ disable/enable in the common > > > > case at the cost of some IRQ allocations taking a slower path. If the PCP > > > > lists need to be refilled, the zone lock still needs to disable IRQs but > > > > that will only happen on PCP refill and drain. If an IRQ is raised when > > > > a PCP allocation is in progress, the trylock will fail and fallback to > > > > using the buddy lists directly. Note that this may not be a universal win > > > > if an interrupt-intensive workload also allocates heavily from interrupt > > > > context and contends heavily on the zone->lock as a result. > > > > > > Hi, > > > > > > This patch caused the following warning. Please take a look. > > > > > > Thanks. > > > > > > WARNING: inconsistent lock state > > > 6.0.0-dbg-DEV #1 Tainted: G S W O > > > -------------------------------- > > > > I finally found time to take a closer look at this and I cannot reproduce > > it against 6.0. What workload triggered the warning, on what platform and > > can you post the kernel config used please? It would also help if you > > can remember what git commit the patch was tested upon. > > > > Thanks and sorry for the long delay. > > I didn't (try to) reproduce this, but FWIW the report looked legit to me, as > after the patch, pcp_spin_trylock() has to be used for both allocation and > freeing to be IRQ safe. free_unref_page() uses it, so it's fine. But as the > stack trace in the report shows, free_unref_page_list() does pcp_spin_lock() > and not _trylock, and that's IMHO the problem. > I completely agree, it was a surprise to me that IO completion would happen in soft IRQ context even though blk_done_softirq indicates that it is normal and I didn't manage to trigger that case myself. I wondered if there was an easy way to force that which would have made testing of this easier. I can live without the reproduction case and cc Yu Zhao after 6.1-rc1 comes out and I've fixed this. -- Mel Gorman SUSE Labs
