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Subject[PATCH] mm: use down_read_killable for locking mmap_sem in access_remote_vm
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This function is used by ptrace and proc files like /proc/pid/cmdline and
/proc/pid/environ. Return 0 (bytes read) if current task is killed.

Mmap_sem could be locked for a long time or forever if something wrong.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
---
mm/memory.c | 4 +++-
mm/nommu.c | 3 ++-
2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 96f1d473c89a..2e6846d09023 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4348,7 +4348,9 @@ int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
void *old_buf = buf;
int write = gup_flags & FOLL_WRITE;

- down_read(&mm->mmap_sem);
+ if (down_read_killable(&mm->mmap_sem))
+ return 0;
+
/* ignore errors, just check how much was successfully transferred */
while (len) {
int bytes, ret, offset;
diff --git a/mm/nommu.c b/mm/nommu.c
index b492fd1fcf9f..cad8fb34088f 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1791,7 +1791,8 @@ int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
struct vm_area_struct *vma;
int write = gup_flags & FOLL_WRITE;

- down_read(&mm->mmap_sem);
+ if (down_read_killable(&mm->mmap_sem))
+ return 0;

/* the access must start within one of the target process's mappings */
vma = find_vma(mm, addr);
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