From: Chris Wright <chrisw@sous-sol.org>
Date: Sat, 22 Jul 2006 16:26:48 +0000 (-0700)
Subject: add fix for existing filemap fix
X-Git-Tag: v2.6.17.7~6
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=aeac910b666c355494c33191b67743b7b42326c3;p=thirdparty%2Fkernel%2Fstable-queue.git

add fix for existing filemap fix
---

diff --git a/pending-2.6.17/generic_file_buffered_write-handle-zero-length-iovec-segments.patch b/pending-2.6.17/generic_file_buffered_write-handle-zero-length-iovec-segments.patch
new file mode 100644
index 00000000000..ce5a311ed32
--- /dev/null
+++ b/pending-2.6.17/generic_file_buffered_write-handle-zero-length-iovec-segments.patch
@@ -0,0 +1,89 @@
+From 81b0c8713385ce1b1b9058e916edcf9561ad76d6 Mon Sep 17 00:00:00 2001
+From: Andrew Morton <akpm@osdl.org>
+Date: Thu, 29 Jun 2006 02:24:26 -0700
+Subject: [PATCH] [PATCH] generic_file_buffered_write(): handle zero-length iovec segments
+
+The recent generic_file_write() deadlock fix caused
+generic_file_buffered_write() to loop inifinitely when presented with a
+zero-length iovec segment.  Fix.
+
+Note that this fix deliberately avoids calling ->prepare_write(),
+->commit_write() etc with a zero-length write.  This is because I don't trust
+all filesystems to get that right.
+
+This is a cautious approach, for 2.6.17.x.  For 2.6.18 we should just go ahead
+and call ->prepare_write() and ->commit_write() with the zero length and fix
+any broken filesystems.  So I'll make that change once this code is stabilised
+and backported into 2.6.17.x.
+
+The reason for preferring to call ->prepare_write() and ->commit_write() with
+the zero-length segment: a zero-length segment _should_ be sufficiently
+uncommon that this is the correct way of handling it.  We don't want to
+optimise for poorly-written userspace at the expense of well-written
+userspace.
+
+Cc: "Vladimir V. Saveliev" <vs@namesys.com>
+Cc: Neil Brown <neilb@suse.de>
+Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
+Cc: Chris Wright <chrisw@sous-sol.org>
+Cc: Greg KH <greg@kroah.com>
+Cc: <stable@kernel.org>
+Cc: walt <wa1ter@myrealbox.com>
+Signed-off-by: Andrew Morton <akpm@osdl.org>
+Signed-off-by: Linus Torvalds <torvalds@osdl.org>
+Signed-off-by: Chris Wright <chrisw@sous-sol.org>
+---
+ mm/filemap.c |    9 ++++++++-
+ mm/filemap.h |    4 ++--
+ 2 files changed, 10 insertions(+), 3 deletions(-)
+
+diff --git a/mm/filemap.c b/mm/filemap.c
+index 4082b3b..648f2c0 100644
+--- a/mm/filemap.c
++++ b/mm/filemap.c
+@@ -2125,6 +2125,12 @@ generic_file_buffered_write(struct kiocb
+ 			break;
+ 		}
+ 
++		if (unlikely(bytes == 0)) {
++			status = 0;
++			copied = 0;
++			goto zero_length_segment;
++		}
++
+ 		status = a_ops->prepare_write(file, page, offset, offset+bytes);
+ 		if (unlikely(status)) {
+ 			loff_t isize = i_size_read(inode);
+@@ -2154,7 +2160,8 @@ generic_file_buffered_write(struct kiocb
+ 			page_cache_release(page);
+ 			continue;
+ 		}
+-		if (likely(copied > 0)) {
++zero_length_segment:
++		if (likely(copied >= 0)) {
+ 			if (!status)
+ 				status = copied;
+ 
+diff --git a/mm/filemap.h b/mm/filemap.h
+index 536979f..3f2a343 100644
+--- a/mm/filemap.h
++++ b/mm/filemap.h
+@@ -88,7 +88,7 @@ filemap_set_next_iovec(const struct iove
+ 	const struct iovec *iov = *iovp;
+ 	size_t base = *basep;
+ 
+-	while (bytes) {
++	do {
+ 		int copy = min(bytes, iov->iov_len - base);
+ 
+ 		bytes -= copy;
+@@ -97,7 +97,7 @@ filemap_set_next_iovec(const struct iove
+ 			iov++;
+ 			base = 0;
+ 		}
+-	}
++	} while (bytes);
+ 	*iovp = iov;
+ 	*basep = base;
+ }
+