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 <[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 2bf210229dafbcc09b70a2c135335f639602ec09..781879a91e3bd1f5d688f59cf4baa78deddf68b2 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;