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Fri, 9 Feb 2018 16:03:45 -0500 Date: Fri, 9 Feb 2018 13:03:39 -0800 From: Andrew Morton To: "Huang, Ying" Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Huang Ying , Konrad Rzeszutek Wilk , Dan Streetman , Seth Jennings , Tetsuo Handa , Shaohua Li , Michal Hocko , Johannes Weiner , Mel Gorman , Shakeel Butt , Boris Ostrovsky , Juergen Gross , stable@vger.kernel.org, Sergey Senozhatsky , Minchan Kim Subject: Re: [PATCH -mm -v3] mm, swap, frontswap: Fix THP swap if frontswap enabled Message-Id: <20180209130339.e91c8709e9c46e5b3f941a29@linux-foundation.org> In-Reply-To: <20180209084947.22749-1-ying.huang@intel.com> References: <20180209084947.22749-1-ying.huang@intel.com> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Fri, 9 Feb 2018 16:49:47 +0800 "Huang, Ying" wrote: > From: Huang Ying > > It was reported by Sergey Senozhatsky that if THP (Transparent Huge > Page) and frontswap (via zswap) are both enabled, when memory goes low > so that swap is triggered, segfault and memory corruption will occur > in random user space applications as follow, > > kernel: urxvt[338]: segfault at 20 ip 00007fc08889ae0d sp 00007ffc73a7fc40 error 6 in libc-2.26.so[7fc08881a000+1ae000] > #0 0x00007fc08889ae0d _int_malloc (libc.so.6) > #1 0x00007fc08889c2f3 malloc (libc.so.6) > #2 0x0000560e6004bff7 _Z14rxvt_wcstoutf8PKwi (urxvt) > #3 0x0000560e6005e75c n/a (urxvt) > #4 0x0000560e6007d9f1 _ZN16rxvt_perl_interp6invokeEP9rxvt_term9hook_typez (urxvt) > #5 0x0000560e6003d988 _ZN9rxvt_term9cmd_parseEv (urxvt) > #6 0x0000560e60042804 _ZN9rxvt_term6pty_cbERN2ev2ioEi (urxvt) > #7 0x0000560e6005c10f _Z17ev_invoke_pendingv (urxvt) > #8 0x0000560e6005cb55 ev_run (urxvt) > #9 0x0000560e6003b9b9 main (urxvt) > #10 0x00007fc08883af4a __libc_start_main (libc.so.6) > #11 0x0000560e6003f9da _start (urxvt) > > After bisection, it was found the first bad commit is > bd4c82c22c367e068 ("mm, THP, swap: delay splitting THP after swapped > out"). > > The root cause is as follow. > > When the pages are written to swap device during swapping out in > swap_writepage(), zswap (fontswap) is tried to compress the pages > instead to improve the performance. But zswap (frontswap) will treat > THP as normal page, so only the head page is saved. After swapping > in, tail pages will not be restored to its original contents, so cause > the memory corruption in the applications. > > This is fixed via rejecting to save page in frontswap store functions > if the page is a THP. So that the THP will be swapped out to swap > device. > > Another choice is to split THP if frontswap is enabled. But it is > found that the frontswap enabling isn't flexible. For example, if > CONFIG_ZSWAP=y (cannot be module), frontswap will be enabled even if > zswap itself isn't enabled. > > Frontswap has multiple backends, to make it easy for one backend to > enable THP support, the THP checking is put in backend frontswap store > functions instead of the general interfaces. > > Fixes: bd4c82c22c367e068 ("mm, THP, swap: delay splitting THP after swapped out") > Reported-by: Sergey Senozhatsky > Tested-by: Sergey Senozhatsky I don't think Sergey has tested this version and I suspect this is a holdover from the earlier patch, so I'll remove this line. > Suggested-by: Minchan Kim # put THP checking in backend > Signed-off-by: "Huang, Ying" > Cc: Konrad Rzeszutek Wilk > Cc: Dan Streetman > Cc: Seth Jennings > Cc: Tetsuo Handa > Cc: Shaohua Li > Cc: Michal Hocko > Cc: Johannes Weiner > Cc: Mel Gorman > Cc: Shakeel Butt > Cc: Boris Ostrovsky > Cc: Juergen Gross > Cc: stable@vger.kernel.org # 4.14