proc: use down_read_killable mmap_sem for /proc/pid/pagemap

Do not remain stuck forever if something goes wrong.  Using a killable
lock permits cleanup of stuck tasks and simplifies investigation.

Link: http://lkml.kernel.org/r/156007493638.3335.4872164955523928492.stgit@buzz
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Reviewed-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Cyrill Gorcunov <gorcunov@gmail.com>
Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 781879a91e3bd1f5d688f59cf4baa78deddf68b2..78bed6adc62d21ff20e8f4d046761df7f2792b47 100644 (file)
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1547,7 +1547,9 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
                /* overflow ? */
                if (end < start_vaddr || end > end_vaddr)
                        end = end_vaddr;
-               down_read(&mm->mmap_sem);
+               ret = down_read_killable(&mm->mmap_sem);
+               if (ret)
+                       goto out_free;
                ret = walk_page_range(start_vaddr, end, &pagemap_walk);
                up_read(&mm->mmap_sem);
                start_vaddr = end;