linux-kernel - Re: [RFC][PATCH 6/8] mm: handle_speculative

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Date:	Tue, 05 Jan 2010 10:37:09 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"minchan.kim@...il.com" <minchan.kim@...il.com>,
	cl@...ux-foundation.org,
	"hugh.dickins" <hugh.dickins@...cali.co.uk>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC][PATCH 6/8] mm: handle_speculative_fault()

On Mon, 2010-01-04 at 19:13 -0800, Linus Torvalds wrote:
> 
> Protecting the vma isn't enough. You need to protect the whole FS stack 
> with rcu. Probably by moving _all_ of "free_vma()" into the RCU path 
> (which means that the whole file/inode gets de-allocated at that later RCU 
> point, rather than synchronously). Not just the actual kfree. 

Right, looking at that I found another interesting challenge, fput() can
sleep and I suspect that even with call_srcu() its callbacks have to be
atomic.

While looking at that code, I found the placement of might_sleep() a tad
confusing, I'd expect that to be in fput() since that is the regular
entry point (all except AIO, which does crazy things).

---
 fs/file_table.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/file_table.c b/fs/file_table.c
index 69652c5..6070c32 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -196,6 +196,8 @@ EXPORT_SYMBOL(alloc_file);
 
 void fput(struct file *file)
 {
+	might_sleep();
+
 	if (atomic_long_dec_and_test(&file->f_count))
 		__fput(file);
 }
@@ -236,8 +238,6 @@ void __fput(struct file *file)
 	struct vfsmount *mnt = file->f_path.mnt;
 	struct inode *inode = dentry->d_inode;
 
-	might_sleep();
-
 	fsnotify_close(file);
 	/*
 	 * The function eventpoll_release() should be the first called


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