On Mon, 27 Jul 2020 16:09:47 +1000, Nicholas Piggin wrote:
> Commit 2f92447f9f96 ("powerpc/book3s64/hash: Use the pte_t address from the
> caller") removed the local_irq_disable from hash_preload, but it was
> required for more than just the page table walk: the hash pte busy bit is
> effectively a lock which may be taken in interrupt context, and the local
> update flag test must not be preempted before it's used.
>
> This solves apparent lockups with perf interrupting __hash_page_64K. If
> get_perf_callchain then also takes a hash fault on the same page while it
> is already locked, it will loop forever taking hash faults, which looks like
> this:
>
> [...]
Applied to powerpc/fixes.
[1/1] powerpc/64s/hash: Fix hash_preload running with interrupts enabled
https://git.kernel.org/powerpc/c/909adfc66b9a1db21b5e8733e9ebfa6cd5135d74
cheers
