The patch titled
Subject: mm: use down_read_killable for locking mmap_sem in access_remote_vm
has been added to the -mm tree. Its filename is
mm-use-down_read_killable-for-locking-mmap_sem-in-access_remote_vm.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-use-down_read_killable-for-locking-mmap_sem-in-access_remote_vm.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-use-down_read_killable-for-locking-mmap_sem-in-access_remote_vm.patch
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------------------------------------------------------
From: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Subject: mm: use down_read_killable for locking mmap_sem in access_remote_vm
This function is used by ptrace and proc files like /proc/pid/cmdline and
/proc/pid/environ.
Access_remote_vm never returns error codes, all errors are ignored and
only size of successfully read data is returned. So, if current task was
killed we'll simply return 0 (bytes read).
Mmap_sem could be locked for a long time or forever if something goes
wrong. Using a killable lock permits cleanup of stuck tasks and
simplifies investigation.
Link: http://lkml.kernel.org/r/156007494202.3335.16782303099589302087.stgit@buzz
Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Reviewed-by: Michal Koutný <mkoutny@xxxxxxxx>
Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxx>
Cc: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 4 +++-
mm/nommu.c | 3 ++-
2 files changed, 5 insertions(+), 2 deletions(-)
--- a/mm/memory.c~mm-use-down_read_killable-for-locking-mmap_sem-in-access_remote_vm
+++ a/mm/memory.c
@@ -4344,7 +4344,9 @@ int __access_remote_vm(struct task_struc
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;
--- a/mm/nommu.c~mm-use-down_read_killable-for-locking-mmap_sem-in-access_remote_vm
+++ a/mm/nommu.c
@@ -1792,7 +1792,8 @@ int __access_remote_vm(struct task_struc
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);
_
Patches currently in -mm which might be from khlebnikov@xxxxxxxxxxxxxx are
proc-use-down_read_killable-mmap_sem-for-proc-pid-maps.patch
proc-use-down_read_killable-mmap_sem-for-proc-pid-smaps_rollup.patch
proc-use-down_read_killable-mmap_sem-for-proc-pid-pagemap.patch
proc-use-down_read_killable-mmap_sem-for-proc-pid-clear_refs.patch
proc-use-down_read_killable-mmap_sem-for-proc-pid-map_files.patch
mm-use-down_read_killable-for-locking-mmap_sem-in-access_remote_vm.patch
