Re: 2.6.2-rc2 nfsd+xfs spins in i_size_read()

[Andrew Morton <akpm@osdl.org>]

Christoph Hellwig <hch@infradead.org> wrote:
>
> On Fri, Jan 30, 2004 at 02:34:59PM -0800, Andrew Morton wrote:
> > If two CPUs hit i_size_write() at the same time we have a bug.  That
> > function requires that the caller provide external serialisation, via i_sem.
> 
> O_APPEND|O_DIRECT writes could do that under XFS..

Sigh.


diff -puN include/linux/fs.h~i_size_write-check include/linux/fs.h
--- 25/include/linux/fs.h~i_size_write-check	Fri Jan 30 15:09:47 2004
+++ 25-akpm/include/linux/fs.h	Fri Jan 30 15:10:28 2004
@@ -464,9 +464,11 @@ static inline loff_t i_size_read(struct 
 #endif
 }
 
+void i_size_write_check(struct inode *inode);
 
 static inline void i_size_write(struct inode *inode, loff_t i_size)
 {
+	i_size_write_check(inode);
 #if BITS_PER_LONG==32 && defined(CONFIG_SMP)
 	write_seqcount_begin(&inode->i_size_seqcount);
 	inode->i_size = i_size;
diff -puN mm/filemap.c~i_size_write-check mm/filemap.c
--- 25/mm/filemap.c~i_size_write-check	Fri Jan 30 15:10:23 2004
+++ 25-akpm/mm/filemap.c	Fri Jan 30 15:11:41 2004
@@ -2010,3 +2010,18 @@ out:
 }
 
 EXPORT_SYMBOL_GPL(generic_file_direct_IO);
+
+void i_size_write_check(struct inode *inode)
+{
+	static int count = 0;
+
+	if (down_trylock(&inode->i_sem) == 0) {
+		if (count < 10) {
+			count++;
+			printk("i_size_write() called without i_sem\n");
+			dump_stack();
+		}
+		up(&inode->i_sem);
+	}
+}
+EXPORT_SYMBOL(i_size_write_check);

_