lkml.org 
[lkml]   [2021]   [Dec]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
Subject[PATCH v3 2/2] mm/oom_kill: allow process_mrelease to run under mmap_lock protection
From
With exit_mmap holding mmap_write_lock during free_pgtables call,
process_mrelease does not need to elevate mm->mm_users in order to
prevent exit_mmap from destrying pagetables while __oom_reap_task_mm
is walking the VMA tree. The change prevents process_mrelease from
calling the last mmput, which can lead to waiting for IO completion
in exit_aio.

Fixes: 337546e83fc7 ("mm/oom_kill.c: prevent a race between process_mrelease and exit_mmap")
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
mm/oom_kill.c | 27 +++++++++++++++------------
1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 1ddabefcfb5a..67780386f478 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -1169,15 +1169,15 @@ SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags)
goto put_task;
}

- if (mmget_not_zero(p->mm)) {
- mm = p->mm;
- if (task_will_free_mem(p))
- reap = true;
- else {
- /* Error only if the work has not been done already */
- if (!test_bit(MMF_OOM_SKIP, &mm->flags))
- ret = -EINVAL;
- }
+ mm = p->mm;
+ mmgrab(mm);
+
+ if (task_will_free_mem(p))
+ reap = true;
+ else {
+ /* Error only if the work has not been done already */
+ if (!test_bit(MMF_OOM_SKIP, &mm->flags))
+ ret = -EINVAL;
}
task_unlock(p);

@@ -1188,13 +1188,16 @@ SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags)
ret = -EINTR;
goto drop_mm;
}
- if (!__oom_reap_task_mm(mm))
+ /*
+ * Check MMF_OOM_SKIP again under mmap_read_lock protection to ensure
+ * possible change in exit_mmap is seen
+ */
+ if (!test_bit(MMF_OOM_SKIP, &mm->flags) && !__oom_reap_task_mm(mm))
ret = -EAGAIN;
mmap_read_unlock(mm);

drop_mm:
- if (mm)
- mmput(mm);
+ mmdrop(mm);
put_task:
put_task_struct(task);
return ret;
--
2.34.1.400.ga245620fadb-goog
\
 
 \ /
  Last update: 2021-12-07 22:51    [W:0.059 / U:0.240 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site