[PATCH AUTOSEL 4.19 094/101] proc: use down_read_killable mmap_sem for /proc/pid/smaps_rollup

[Sasha Levin <sashal@kernel.org>]

From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>

[ Upstream commit a26a97815548574213fd37f29b4b78ccc6d9ed20 ]

Do not remain stuck forever if something goes wrong.  Using a killable
lock permits cleanup of stuck tasks and simplifies investigation.

Link: http://lkml.kernel.org/r/156007493429.3335.14666825072272692455.stgit@buzz
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>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/proc/task_mmu.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index c5819baee35c..b2010055180e 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -826,7 +826,10 @@ static int show_smaps_rollup(struct seq_file *m, void *v)
 
 	memset(&mss, 0, sizeof(mss));
 
-	down_read(&mm->mmap_sem);
+	ret = down_read_killable(&mm->mmap_sem);
+	if (ret)
+		goto out_put_mm;
+
 	hold_task_mempolicy(priv);
 
 	for (vma = priv->mm->mmap; vma; vma = vma->vm_next) {
@@ -843,8 +846,9 @@ static int show_smaps_rollup(struct seq_file *m, void *v)
 
 	release_task_mempolicy(priv);
 	up_read(&mm->mmap_sem);
-	mmput(mm);
 
+out_put_mm:
+	mmput(mm);
 out_put_task:
 	put_task_struct(priv->task);
 	priv->task = NULL;
-- 
2.20.1