From 7762f5a0b709b415fda132258ad37b9f2a1db994 Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <miklos@szeredi.hu>
Date: Tue, 17 Oct 2006 00:10:07 -0700
Subject: [PATCH] [PATCH] document i_size_write locking rules
Unless someone reads the documentation for write_seqcount_{begin,end} it is
not obvious, that i_size_write() needs locking. Especially, that lack of such
locking can result in a system hang.
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---
include/linux/fs.h | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 34406ed467c35..661c7c5721492 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -656,7 +656,11 @@ static inline loff_t i_size_read(struct inode *inode)
#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)