From b25749a58cae52de28ddc5d642531f9f6b01084c Mon Sep 17 00:00:00 2001 From: =?utf8?q?Fabian=20Gr=C3=BCnbichler?= Date: Wed, 28 Mar 2018 15:14:00 +0200 Subject: [PATCH] fix #1633: potential deadlock with shmem MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Signed-off-by: Fabian Grünbichler --- ...wait-for-lock_page-in-shmem_unused_h.patch | 103 ++++++++++++++++++ 1 file changed, 103 insertions(+) create mode 100644 patches/kernel/0007-mm-shmem-do-not-wait-for-lock_page-in-shmem_unused_h.patch diff --git a/patches/kernel/0007-mm-shmem-do-not-wait-for-lock_page-in-shmem_unused_h.patch b/patches/kernel/0007-mm-shmem-do-not-wait-for-lock_page-in-shmem_unused_h.patch new file mode 100644 index 0000000..9d640ed --- /dev/null +++ b/patches/kernel/0007-mm-shmem-do-not-wait-for-lock_page-in-shmem_unused_h.patch @@ -0,0 +1,103 @@ +From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 +From: "Kirill A. Shutemov" +Date: Fri, 23 Mar 2018 09:19:21 +0100 +Subject: [PATCH] mm/shmem: do not wait for lock_page() in + shmem_unused_huge_shrink() +MIME-Version: 1.0 +Content-Type: text/plain; charset=UTF-8 +Content-Transfer-Encoding: 8bit + +shmem_unused_huge_shrink() gets called from reclaim path. Waiting for +page lock may lead to deadlock there. + +There was a bug report that may be attributed to this: + +http://lkml.kernel.org/r/alpine.LRH.2.11.1801242349220.30642@mail.ewheeler.net + +Replace lock_page() with trylock_page() and skip the page if we failed to +lock it. We will get to the page on the next scan. + +We can test for the PageTransHuge() outside the page lock as we only need +protection against splitting the page under us. Holding pin oni the page +is enough for this. + +Link: http://lkml.kernel.org/r/20180316210830.43738-1-kirill.shutemov@linux.intel.com +Fixes: 779750d20b93 ("shmem: split huge pages beyond i_size under memory pressure") +Signed-off-by: Kirill A. Shutemov +Reported-by: Eric Wheeler +Acked-by: Michal Hocko +Reviewed-by: Andrew Morton +Cc: Tetsuo Handa +Cc: Hugh Dickins +Cc: [4.8+] +Signed-off-by: Andrew Morton <> +(cherry-picked from https://git.kernel.org/pub/scm/linux/kernel/git/mhocko/mm.git/commit/?h=since-4.15&id=73eccc61c701ee7b4223aea2079542a712feeea7) +Signed-off-by: Fabian Grünbichler +--- + mm/shmem.c | 31 ++++++++++++++++++++----------- + 1 file changed, 20 insertions(+), 11 deletions(-) + +diff --git a/mm/shmem.c b/mm/shmem.c +index f6695c111086..800482fe6ed6 100644 +--- a/mm/shmem.c ++++ b/mm/shmem.c +@@ -497,36 +497,45 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo, + info = list_entry(pos, struct shmem_inode_info, shrinklist); + inode = &info->vfs_inode; + +- if (nr_to_split && split >= nr_to_split) { +- iput(inode); +- continue; +- } ++ if (nr_to_split && split >= nr_to_split) ++ goto leave; + +- page = find_lock_page(inode->i_mapping, ++ page = find_get_page(inode->i_mapping, + (inode->i_size & HPAGE_PMD_MASK) >> PAGE_SHIFT); + if (!page) + goto drop; + ++ /* No huge page at the end of the file: nothing to split */ + if (!PageTransHuge(page)) { +- unlock_page(page); + put_page(page); + goto drop; + } + ++ /* ++ * Leave the inode on the list if we failed to lock ++ * the page at this time. ++ * ++ * Waiting for the lock may lead to deadlock in the ++ * reclaim path. ++ */ ++ if (!trylock_page(page)) { ++ put_page(page); ++ goto leave; ++ } ++ + ret = split_huge_page(page); + unlock_page(page); + put_page(page); + +- if (ret) { +- /* split failed: leave it on the list */ +- iput(inode); +- continue; +- } ++ /* If split failed leave the inode on the list */ ++ if (ret) ++ goto leave; + + split++; + drop: + list_del_init(&info->shrinklist); + removed++; ++leave: + iput(inode); + } + +-- +2.14.2 + -- 2.39.2