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 <[email protected]>
Reviewed-by: Roman Gushchin <[email protected]>
Reviewed-by: Cyrill Gorcunov <[email protected]>
Reviewed-by: Kirill Tkhai <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Michal Koutný <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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;