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

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/156007493429.3335.14666825072272692455.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 2bf2102..781879a 100644 (file)
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -832,7 +832,10 @@ static int show_smaps_rollup(struct seq_file *m, void *v)
 
        memset(&mss, 0, sizeof(mss));
 
-       down_read(&mm->mmap_sem);
+       ret = down_read_killable(&mm->mmap_sem);
+       if (ret)
+               goto out_put_mm;
+
        hold_task_mempolicy(priv);
 
        for (vma = priv->mm->mmap; vma; vma = vma->vm_next) {
@@ -849,8 +852,9 @@ static int show_smaps_rollup(struct seq_file *m, void *v)
 
        release_task_mempolicy(priv);
        up_read(&mm->mmap_sem);
-       mmput(mm);
 
+out_put_mm:
+       mmput(mm);
 out_put_task:
        put_task_struct(priv->task);
        priv->task = NULL;