Re: [PATCH 11/18] coredump: make coredump_wait wait for mma_sem for write killable

From: Vlastimil Babka
Date: Fri Mar 11 2016 - 06:33:12 EST

On 02/29/2016 02:26 PM, Michal Hocko wrote:
From: Michal Hocko <mhocko@xxxxxxxx>

coredump_wait waits for mmap_sem for write currently which can
prevent oom_reaper to reclaim the oom victims address space
asynchronously because that requires mmap_sem for read. This might
happen if the oom victim is multi threaded and some thread(s) is
holding mmap_sem for read (e.g. page fault) and it is stuck in
the page allocator while other thread(s) reached coredump_wait

This patch simply uses down_write_killable and bails out with EINTR
if the lock got interrupted by the fatal signal. do_coredump will
return right away and do_group_exit will take care to zap the whole
thread group.

Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

fs/coredump.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index 9ea87e9fdccf..6b8aa1629891 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -410,7 +410,9 @@ static int coredump_wait(int exit_code, struct core_state *core_state)
core_state->dumper.task = tsk;
core_state-> = NULL;

- down_write(&mm->mmap_sem);
+ if (down_write_killable(&mm->mmap_sem))
+ return -EINTR;
if (!mm->core_state)
core_waiters = zap_threads(tsk, mm, core_state, exit_code);