coredump: make coredump_wait wait for mmap_sem for write killable

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 already.

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.

Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/coredump.c b/fs/coredump.c
index 492c2db..38a7ab8 100644 (file)
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -413,7 +413,9 @@ static int coredump_wait(int exit_code, struct core_state *core_state)
        core_state->dumper.task = tsk;
        core_state->dumper.next = 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);
        up_write(&mm->mmap_sem);