The patch titled Subject: mm, swap, frontswap: Fix THP swap if frontswap enabled has been added to the -mm tree. Its filename is mm-swap-frontswap-fix-thp-swap-if-frontswap-enabled.patch

This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-swap-frontswap-fix-thp-swap-if-f... and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-swap-frontswap-fix-thp-swap-if-f...

Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/SubmitChecklist when testing your code ***

The -mm tree is included into linux-next and is updated there every 3-4 working days

------------------------------------------------------ From: Huang Ying huang.ying.caritas@gmail.com Subject: mm, swap, frontswap: Fix THP swap if frontswap enabled

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 follows:

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 splitting THP before writing the page to swap device if frontswap is enabled. To deal with the situation where frontswap is enabled at runtime, whether the page is THP is checked before using frontswap during swapping out too.

Link: http://lkml.kernel.org/r/20180207070035.30302-1-ying.huang@intel.com Fixes: bd4c82c22c367e068 ("mm, THP, swap: delay splitting THP after swapped out") Signed-off-by: "Huang, Ying" ying.huang@intel.com Reported-by: Sergey Senozhatsky sergey.senozhatsky@gmail.com Tested-by: Sergey Senozhatsky sergey.senozhatsky@gmail.com Cc: Konrad Rzeszutek Wilk konrad.wilk@oracle.com Cc: Dan Streetman ddstreet@ieee.org Cc: Seth Jennings sjenning@redhat.com Cc: Minchan Kim minchan@kernel.org Cc: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Cc: Shaohua Li shli@kernel.org Cc: Michal Hocko mhocko@suse.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Mel Gorman mgorman@techsingularity.net Cc: Shakeel Butt shakeelb@google.com Cc: stable@vger.kernel.org [4.14+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/page_io.c | 2 +- mm/swapfile.c | 3 +++ 2 files changed, 4 insertions(+), 1 deletion(-)

diff -puN mm/page_io.c~mm-swap-frontswap-fix-thp-swap-if-frontswap-enabled mm/page_io.c --- a/mm/page_io.c~mm-swap-frontswap-fix-thp-swap-if-frontswap-enabled +++ a/mm/page_io.c @@ -250,7 +250,7 @@ int swap_writepage(struct page *page, st unlock_page(page); goto out; } - if (frontswap_store(page) == 0) { + if (!PageTransHuge(page) && frontswap_store(page) == 0) { set_page_writeback(page); unlock_page(page); end_page_writeback(page); diff -puN mm/swapfile.c~mm-swap-frontswap-fix-thp-swap-if-frontswap-enabled mm/swapfile.c --- a/mm/swapfile.c~mm-swap-frontswap-fix-thp-swap-if-frontswap-enabled +++ a/mm/swapfile.c @@ -934,6 +934,9 @@ int get_swap_pages(int n_goal, bool clus

/* Only single cluster request supported */ WARN_ON_ONCE(n_goal > 1 && cluster); + /* Frontswap doesn't support THP */ + if (frontswap_enabled() && cluster) + goto noswap;

avail_pgs = atomic_long_read(&nr_swap_pages) / nr_pages; if (avail_pgs <= 0) _

Patches currently in -mm which might be from huang.ying.caritas@gmail.com are

mm-swap-frontswap-fix-thp-swap-if-frontswap-enabled.patch fontswap-thp-fix.patch