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Subject: [PATCH v2 4/6] proc: use down_read_killable mmap_sem for
 /proc/pid/clear_refs
From:   Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
To:     linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org
Cc:     Oleg Nesterov <oleg@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Michal Hocko <mhocko@kernel.org>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Kirill Tkhai <ktkhai@virtuozzo.com>,
        Michal =?utf-8?q?Koutn=C3=BD?= <mkoutny@suse.com>,
        Al Viro <viro@zeniv.linux.org.uk>, Roman Gushchin <guro@fb.com>
Date:   Sun, 09 Jun 2019 13:08:58 +0300
Message-ID: <156007493826.3335.5424884725467456239.stgit@buzz>
In-Reply-To: <156007465229.3335.10259979070641486905.stgit@buzz>
References: <156007465229.3335.10259979070641486905.stgit@buzz>
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Do not stuck forever if something wrong.
Killable lock allows to cleanup stuck tasks and simplifies investigation.

Replace the only unkillable mmap_sem lock in clear_refs_write.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Reviewed-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Cyrill Gorcunov <gorcunov@gmail.com>
Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Michal Hocko <mhocko@suse.com>
---
 fs/proc/task_mmu.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 78bed6adc62d..7f84d1477b5b 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1140,7 +1140,10 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
 			goto out_mm;
 		}
 
-		down_read(&mm->mmap_sem);
+		if (down_read_killable(&mm->mmap_sem)) {
+			count = -EINTR;
+			goto out_mm;
+		}
 		tlb_gather_mmu(&tlb, mm, 0, -1);
 		if (type == CLEAR_REFS_SOFT_DIRTY) {
 			for (vma = mm->mmap; vma; vma = vma->vm_next) {