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Subject[PATCH v2 1/6] proc: use down_read_killable mmap_sem for /proc/pid/maps
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Do not stuck forever if something wrong.
Killable lock allows to cleanup stuck tasks and simplifies investigation.

This function also used for /proc/pid/smaps.

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 | 6 +++++-
fs/proc/task_nommu.c | 6 +++++-
2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 01d4eb0e6bd1..2bf210229daf 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -166,7 +166,11 @@ static void *m_start(struct seq_file *m, loff_t *ppos)
if (!mm || !mmget_not_zero(mm))
return NULL;

- down_read(&mm->mmap_sem);
+ if (down_read_killable(&mm->mmap_sem)) {
+ mmput(mm);
+ return ERR_PTR(-EINTR);
+ }
+
hold_task_mempolicy(priv);
priv->tail_vma = get_gate_vma(mm);

diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c
index 36bf0f2e102e..7907e6419e57 100644
--- a/fs/proc/task_nommu.c
+++ b/fs/proc/task_nommu.c
@@ -211,7 +211,11 @@ static void *m_start(struct seq_file *m, loff_t *pos)
if (!mm || !mmget_not_zero(mm))
return NULL;

- down_read(&mm->mmap_sem);
+ if (down_read_killable(&mm->mmap_sem)) {
+ mmput(mm);
+ return ERR_PTR(-EINTR);
+ }
+
/* start from the Nth VMA */
for (p = rb_first(&mm->mm_rb); p; p = rb_next(p))
if (n-- == 0)
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