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Date: Mon, 16 Oct 2006 16:51:25 -0700
From: Andrew Morton <akpm@...l.org>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [patch 01/12] fuse: fix hang on SMP
On Mon, 16 Oct 2006 18:27:10 +0200
Miklos Szeredi <miklos@...redi.hu> wrote:
> Fuse didn't always call i_size_write() with i_mutex held which caused
> rare hangs on SMP/32bit.
Yes, that is a bit of a trap. I'll maintain a patch in -mm which spits a
warning if i_size_write() is called without i_mutex held.
--- a/include/linux/fs.h~mm-only-i_size_write-debugging
+++ a/include/linux/fs.h
@@ -646,25 +646,7 @@ static inline loff_t i_size_read(struct
#endif
}
-/*
- * NOTE: unlike i_size_read(), i_size_write() does need locking around it
- * (normally i_mutex), otherwise on 32bit/SMP an update of i_size_seqcount
- * can be lost, resulting in subsequent i_size_read() calls spinning forever.
- */
-static inline void i_size_write(struct inode *inode, loff_t i_size)
-{
-#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
- write_seqcount_begin(&inode->i_size_seqcount);
- inode->i_size = i_size;
- write_seqcount_end(&inode->i_size_seqcount);
-#elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPT)
- preempt_disable();
- inode->i_size = i_size;
- preempt_enable();
-#else
- inode->i_size = i_size;
-#endif
-}
+void i_size_write(struct inode *inode, loff_t i_size);
static inline unsigned iminor(struct inode *inode)
{
diff -puN fs/inode.c~mm-only-i_size_write-debugging fs/inode.c
--- a/fs/inode.c~mm-only-i_size_write-debugging
+++ a/fs/inode.c
@@ -1384,6 +1384,23 @@ void __init inode_init(unsigned long mem
INIT_HLIST_HEAD(&inode_hashtable[loop]);
}
+void i_size_write(struct inode *inode, loff_t i_size)
+{
+ WARN_ON_ONCE(!mutex_is_locked(&inode->i_mutex));
+#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
+ write_seqcount_begin(&inode->i_size_seqcount);
+ inode->i_size = i_size;
+ write_seqcount_end(&inode->i_size_seqcount);
+#elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPT)
+ preempt_disable();
+ inode->i_size = i_size;
+ preempt_enable();
+#else
+ inode->i_size = i_size;
+#endif
+}
+EXPORT_SYMBOL(i_size_write);
+
void init_special_inode(struct inode *inode, umode_t mode, dev_t rdev)
{
inode->i_mode = mode;
_
-
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