Re: [RFC][PATCH 6/8] mm: handle_speculative_fault()

[Peter Zijlstra]

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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