proc: add a schedule point in proc_pid_readdir()

[ Upstream commit 3ba4bce ]

We have seen proc_pid_readdir() invocations holding cpu for more than 50
ms.  Add a cond_resched() to be gentle with other tasks.

[[email protected]: coding style fix]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Eric Dumazet <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Signed-off-by: Sasha Levin <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Eric Dumazet

fs/proc/base.c

@@ -3181,6 +3181,8 @@ int proc_pid_readdir(struct file *file, struct dir_context *ctx)
 	     iter.tgid += 1, iter = next_tgid(ns, iter)) {
 		char name[PROC_NUMBUF];
 		int len;
+
+		cond_resched();
 		if (!has_pid_permissions(ns, iter.task, 2))
 			continue;