linux-kernel - [PATCH] proc: add a reschedule point in proc_readfd

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Message-ID: <1449169927.25029.10.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 03 Dec 2015 11:12:07 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [PATCH] proc: add a reschedule point in proc_readfd_common()

From: Eric Dumazet <edumazet@...gle.com>

User can pass an arbitrary large buffer to getdents().

It is typically a 32KB buffer used by libc scandir() implementation.

When scanning /proc/{pid}/fd, we can hold cpu way too long,
so add a cond_resched() to be kind with other tasks.

We've seen latencies of more than 50ms on real workloads.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
---
 fs/proc/fd.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 3c2a915c695a..56afa5ef08f2 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -258,6 +258,7 @@ static int proc_readfd_common(struct file *file, struct dir_context *ctx,
 				     name, len, instantiate, p,
 				     (void *)(unsigned long)fd))
 			goto out_fd_loop;
+		cond_resched();
 		rcu_read_lock();
 	}
 	rcu_read_unlock();


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