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[14.202.194.140]) by smtp.gmail.com with ESMTPSA id p75-v6sm4299662pfi.22.2018.09.25.05.15.07 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 25 Sep 2018 05:15:08 -0700 (PDT) Date: Tue, 25 Sep 2018 22:15:04 +1000 From: Balbir Singh To: David Hildenbrand Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-acpi@vger.kernel.org, xen-devel@lists.xenproject.org, devel@linuxdriverproject.org, Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Rashmica Gupta , Michael Neuling Subject: Re: [PATCH v2 5/6] powerpc/powernv: hold device_hotplug_lock when calling memtrace_offline_pages() Message-ID: <20180925121504.GH8537@350D> References: <20180925091457.28651-1-david@redhat.com> <20180925091457.28651-6-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180925091457.28651-6-david@redhat.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 25, 2018 at 11:14:56AM +0200, David Hildenbrand wrote: > Let's perform all checking + offlining + removing under > device_hotplug_lock, so nobody can mess with these devices via > sysfs concurrently. > > Cc: Benjamin Herrenschmidt > Cc: Paul Mackerras > Cc: Michael Ellerman > Cc: Rashmica Gupta > Cc: Balbir Singh > Cc: Michael Neuling > Reviewed-by: Pavel Tatashin > Reviewed-by: Rashmica Gupta > Signed-off-by: David Hildenbrand > --- > arch/powerpc/platforms/powernv/memtrace.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/platforms/powernv/memtrace.c b/arch/powerpc/platforms/powernv/memtrace.c > index fdd48f1a39f7..d84d09c56af9 100644 > --- a/arch/powerpc/platforms/powernv/memtrace.c > +++ b/arch/powerpc/platforms/powernv/memtrace.c > @@ -70,6 +70,7 @@ static int change_memblock_state(struct memory_block *mem, void *arg) > return 0; > } > > +/* called with device_hotplug_lock held */ > static bool memtrace_offline_pages(u32 nid, u64 start_pfn, u64 nr_pages) > { > u64 end_pfn = start_pfn + nr_pages - 1; > @@ -111,6 +112,7 @@ static u64 memtrace_alloc_node(u32 nid, u64 size) > end_pfn = round_down(end_pfn - nr_pages, nr_pages); > > for (base_pfn = end_pfn; base_pfn > start_pfn; base_pfn -= nr_pages) { > + lock_device_hotplug(); Why not grab the lock before the for loop? That way we can avoid bad cases like a large node being scanned for a small number of pages (nr_pages). Ideally we need a cond_resched() in the loop, but I guess offline_pages() has one. Acked-by: Balbir Singh