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Wysocki" Cc: James Morse , linux-mm@kvack.org, linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Naoya Horiguchi , Len Brown , Tony Luck , Borislav Petkov , Catalin Marinas , Will Deacon , Mark Rutland , Tyler Baicar , Xie XiuQi Subject: Re: [PATCH v2 1/3] mm/memory-failure: Add memory_failure_queue_kick() Message-Id: <20200518125828.e4e3973c743556e976c5ee65@linux-foundation.org> In-Reply-To: <49686237.p6yG9EJavU@kreacher> References: <20200501164543.24423-1-james.morse@arm.com> <20200501164543.24423-2-james.morse@arm.com> <49686237.p6yG9EJavU@kreacher> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, 18 May 2020 14:45:05 +0200 "Rafael J. Wysocki" wrote: > On Friday, May 1, 2020 6:45:41 PM CEST James Morse wrote: > > The GHES code calls memory_failure_queue() from IRQ context to schedule > > work on the current CPU so that memory_failure() can sleep. > > > > For synchronous memory errors the arch code needs to know any signals > > that memory_failure() will trigger are pending before it returns to > > user-space, possibly when exiting from the IRQ. > > > > Add a helper to kick the memory failure queue, to ensure the scheduled > > work has happened. This has to be called from process context, so may > > have been migrated from the original cpu. Pass the cpu the work was > > queued on. > > > > Change memory_failure_work_func() to permit being called on the 'wrong' > > cpu. > > > > --- a/include/linux/mm.h > > +++ b/include/linux/mm.h > > @@ -3012,6 +3012,7 @@ enum mf_flags { > > }; > > extern int memory_failure(unsigned long pfn, int flags); > > extern void memory_failure_queue(unsigned long pfn, int flags); > > +extern void memory_failure_queue_kick(int cpu); > > extern int unpoison_memory(unsigned long pfn); > > extern int get_hwpoison_page(struct page *page); > > #define put_hwpoison_page(page) put_page(page) > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > > index a96364be8ab4..c4afb407bf0f 100644 > > --- a/mm/memory-failure.c > > +++ b/mm/memory-failure.c > > @@ -1493,7 +1493,7 @@ static void memory_failure_work_func(struct work_struct *work) > > unsigned long proc_flags; > > int gotten; > > > > - mf_cpu = this_cpu_ptr(&memory_failure_cpu); > > + mf_cpu = container_of(work, struct memory_failure_cpu, work); > > for (;;) { > > spin_lock_irqsave(&mf_cpu->lock, proc_flags); > > gotten = kfifo_get(&mf_cpu->fifo, &entry); > > @@ -1507,6 +1507,19 @@ static void memory_failure_work_func(struct work_struct *work) > > } > > } > > > > +/* > > + * Process memory_failure work queued on the specified CPU. > > + * Used to avoid return-to-userspace racing with the memory_failure workqueue. > > + */ > > +void memory_failure_queue_kick(int cpu) > > +{ > > + struct memory_failure_cpu *mf_cpu; > > + > > + mf_cpu = &per_cpu(memory_failure_cpu, cpu); > > + cancel_work_sync(&mf_cpu->work); > > + memory_failure_work_func(&mf_cpu->work); > > +} > > + > > static int __init memory_failure_init(void) > > { > > struct memory_failure_cpu *mf_cpu; > > > > I could apply this provided an ACK from the mm people. > Naoya Horiguchi is the memory-failure.c person. A review would be appreciated please? I'm struggling with it a bit. memory_failure_queue_kick() should be called on the cpu which is identified by arg `cpu', yes? memory_failure_work_func() appears to assume this. If that's right then a) why bother passing in the `cpu' arg? and b) what keeps this thread pinned to that CPU? cancel_work_sync() can schedule.