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[31.128.146.191]) by smtp.gmail.com with ESMTPSA id q128-v6sm3374469ljq.14.2019.02.13.03.51.17 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 13 Feb 2019 03:51:17 -0800 (PST) From: Yury Norov X-Google-Original-From: Yury Norov Date: Wed, 13 Feb 2019 14:51:15 +0300 To: Mel Gorman Cc: Yury Norov , Vlastimil Babka , Andrea Arcangeli , David Rientjes , Michal Hocko , Zi Yan , Andrew Morton , Linus Torvalds , Will Deacon , Catalin Marinas , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: 5.0-rc kernel hangs on early boot Message-ID: <20190213115115.GA8928@yury-thinkpad> References: <20190213082134.GA21834@yury-thinkpad> <20190213111409.GN9565@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190213111409.GN9565@techsingularity.net> 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 Wed, Feb 13, 2019 at 11:14:09AM +0000, Mel Gorman wrote: > On Wed, Feb 13, 2019 at 11:25:40AM +0300, Yury Norov wrote: > > Hi Mel, all, > > > > My kernel on qemu/arm64 setup hangs at early boot since v5.0-rc1. > > Backtrace is not too verbose: > > (gdb) i threads > > Id Target Id Frame > > * 1 Thread 1 (CPU#0 [running]) 0xffff000010a49b74 in __delay (cycles=4096) > > at arch/arm64/lib/delay.c:49 > > 2 Thread 2 (CPU#1 [halted ]) 0x0000000000000000 in ?? () > > 3 Thread 3 (CPU#2 [halted ]) 0x0000000000000000 in ?? () > > 4 Thread 4 (CPU#3 [halted ]) 0x0000000000000000 in ?? () > > (gdb) bt > > #0 0xffff000010a49b74 in __delay (cycles=4096) at arch/arm64/lib/delay.c:49 > > Backtrace stopped: previous frame identical to this frame (corrupt stack?) > > > > Reverting the patch > > 1c30844d2dfe272d58c ("mm: reclaim small amounts of memory when an external > > fragmentation event occurs") together with following patch > > 73444bc4d8f92e46a20 ("mm, page_alloc: do not wake kswapd with zone lock held") > > helps me to boot normally. > > > > Well, that's a bad start to any day. Thanks for tracking it down. Does > the following patch help? I can't test it properly as I didn't recreate > your boot image or initrd but this appears to get past the initial boot > phase at least. Hi Mel, The patch works for me. The day gets better indeed. :-) Tested-by: Yury Norov Yury > ---8<--- > mm, page_alloc: Fix a division by zero error when boosting watermarks > > Yury Norov reported that an arm64 KVM instance could not boot since after > v5.0-rc1 and could addressed by reverting the patches > > 1c30844d2dfe272d58c ("mm: reclaim small amounts of memory when an external > 73444bc4d8f92e46a20 ("mm, page_alloc: do not wake kswapd with zone lock held") > > The problem is that a division by zero error is possible if boosting occurs > either very early in boot or if the high watermark is very small. This > patch checks for the conditions and avoids boosting in those cases. > > Fixes: 1c30844d2dfe ("mm: reclaim small amounts of memory when an external fragmentation event occurs") > Reported-by: Yury Norov > Signed-off-by: Mel Gorman > > --- > mm/page_alloc.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index d295c9bc01a8..ae7e4ba5b9f5 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -2170,6 +2170,11 @@ static inline void boost_watermark(struct zone *zone) > > max_boost = mult_frac(zone->_watermark[WMARK_HIGH], > watermark_boost_factor, 10000); > + > + /* high watermark be be uninitialised or very small */ > + if (!max_boost) > + return; > + > max_boost = max(pageblock_nr_pages, max_boost); > > zone->watermark_boost = min(zone->watermark_boost + pageblock_nr_pages, >