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authorAndrea Arcangeli <aarcange@redhat.com>2017-09-07 02:25:00 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2017-09-07 03:27:30 +0300
commit212925802454672e6cd2949a727f5e2c1377bf06 (patch)
treefb3a18e24da3081e5ed3690e3908274a20f8886d /mm/mmap.c
parenta2468cc9bfdff6139f59ca896671e5819ff5f94a (diff)
downloadlinux-212925802454672e6cd2949a727f5e2c1377bf06.tar.xz
mm: oom: let oom_reap_task and exit_mmap run concurrently
This is purely required because exit_aio() may block and exit_mmap() may never start, if the oom_reap_task cannot start running on a mm with mm_users == 0. At the same time if the OOM reaper doesn't wait at all for the memory of the current OOM candidate to be freed by exit_mmap->unmap_vmas, it would generate a spurious OOM kill. If it wasn't because of the exit_aio or similar blocking functions in the last mmput, it would be enough to change the oom_reap_task() in the case it finds mm_users == 0, to wait for a timeout or to wait for __mmput to set MMF_OOM_SKIP itself, but it's not just exit_mmap the problem here so the concurrency of exit_mmap and oom_reap_task is apparently warranted. It's a non standard runtime, exit_mmap() runs without mmap_sem, and oom_reap_task runs with the mmap_sem for reading as usual (kind of MADV_DONTNEED). The race between the two is solved with a combination of tsk_is_oom_victim() (serialized by task_lock) and MMF_OOM_SKIP (serialized by a dummy down_write/up_write cycle on the same lines of the ksm_exit method). If the oom_reap_task() may be running concurrently during exit_mmap, exit_mmap will wait it to finish in down_write (before taking down mm structures that would make the oom_reap_task fail with use after free). If exit_mmap comes first, oom_reap_task() will skip the mm if MMF_OOM_SKIP is already set and in turn all memory is already freed and furthermore the mm data structures may already have been taken down by free_pgtables. [aarcange@redhat.com: incremental one liner] Link: http://lkml.kernel.org/r/20170726164319.GC29716@redhat.com [rientjes@google.com: remove unused mmput_async] Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1708141733130.50317@chino.kir.corp.google.com [aarcange@redhat.com: microoptimization] Link: http://lkml.kernel.org/r/20170817171240.GB5066@redhat.com Link: http://lkml.kernel.org/r/20170726162912.GA29716@redhat.com Fixes: 26db62f179d1 ("oom: keep mm of the killed task available") Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: David Rientjes <rientjes@google.com> Reported-by: David Rientjes <rientjes@google.com> Tested-by: David Rientjes <rientjes@google.com> Reviewed-by: Michal Hocko <mhocko@suse.com> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/mmap.c')
-rw-r--r--mm/mmap.c18
1 files changed, 18 insertions, 0 deletions
diff --git a/mm/mmap.c b/mm/mmap.c
index 52f6c6b18f40..4c5981651407 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -44,6 +44,7 @@
#include <linux/userfaultfd_k.h>
#include <linux/moduleparam.h>
#include <linux/pkeys.h>
+#include <linux/oom.h>
#include <linux/uaccess.h>
#include <asm/cacheflush.h>
@@ -3001,6 +3002,23 @@ void exit_mmap(struct mm_struct *mm)
/* Use -1 here to ensure all VMAs in the mm are unmapped */
unmap_vmas(&tlb, vma, 0, -1);
+ set_bit(MMF_OOM_SKIP, &mm->flags);
+ if (unlikely(tsk_is_oom_victim(current))) {
+ /*
+ * Wait for oom_reap_task() to stop working on this
+ * mm. Because MMF_OOM_SKIP is already set before
+ * calling down_read(), oom_reap_task() will not run
+ * on this "mm" post up_write().
+ *
+ * tsk_is_oom_victim() cannot be set from under us
+ * either because current->mm is already set to NULL
+ * under task_lock before calling mmput and oom_mm is
+ * set not NULL by the OOM killer only if current->mm
+ * is found not NULL while holding the task_lock.
+ */
+ down_write(&mm->mmap_sem);
+ up_write(&mm->mmap_sem);
+ }
free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, USER_PGTABLES_CEILING);
tlb_finish_mmu(&tlb, 0, -1);