linux-kernel - Re: [PATCH] task_work: remove fifo ordering guarantee

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Date:	Sat, 29 Aug 2015 07:11:13 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Maciej Żenczykowski <maze@...gle.com>
Subject: Re: [PATCH] task_work: remove fifo ordering guarantee

On Sat, 2015-08-29 at 06:57 -0700, Eric Dumazet wrote:

> Now we also could question why we needed commit
> 4a9d4b024a3102fc083c925c242d98ac27b1c5f6 ("switch fput to task_work_add
> ") since it seems quite an overhead at task exit with 10^6 of files to
> close.
> 
> I understood the 'schedule_work() for interrupt/kernel_thread callers'
> part, but not the task_work_add() one.

If this needs to be kept, maybe then add following, to make sure
we flush the list at most every BITS_PER_LONG files

diff --git a/fs/file.c b/fs/file.c
index 6c672ad329e9..f3d0a79cef05 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -22,6 +22,7 @@
 #include <linux/spinlock.h>
 #include <linux/rcupdate.h>
 #include <linux/workqueue.h>
+#include <linux/task_work.h>
 
 int sysctl_nr_open __read_mostly = 1024*1024;
 int sysctl_nr_open_min = BITS_PER_LONG;
@@ -392,6 +393,7 @@ static struct fdtable *close_files(struct
files_struct * files)
 			i++;
 			set >>= 1;
 		}
+		task_work_run();
 	}
 
 	return fdt;


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