From: Miklos Szeredi <miklos@szeredi.hu>
Date: Tue, 17 Oct 2006 07:10:07 +0000 (-0700)
Subject: [PATCH] document i_size_write locking rules
X-Git-Tag: v2.6.19-rc3~179
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7762f5a0b709b415fda132258ad37b9f2a1db994;p=linux-2.6

[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>
---

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 34406ed467..661c7c5721 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)