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Subject[PATCH v2 2/6] proc: use down_read_killable mmap_sem for /proc/pid/smaps_rollup
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Do not stuck forever if something wrong.
Killable lock allows to cleanup stuck tasks and simplifies investigation.

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 | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 2bf210229daf..781879a91e3b 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -832,7 +832,10 @@ 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) {
@@ -849,8 +852,9 @@ 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;
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