[PATCH] Bug in fs/afs/write.c function afs_write_back_from_locked_page()

[PATCH] Bug in fs/afs/write.c function afs_write_back_from_locked_page()

[Mika Kukkonen]

Following bug was uncovered by compiling with '-W' flag:

  CC [M]  fs/afs/write.o
fs/afs/write.c: In function ‘afs_write_back_from_locked_page’:
fs/afs/write.c:398: warning: comparison of unsigned expression >= 0 is always true

Loop variable 'n' is unsigned, so wraps around happily as far as I can
see. Trival fix attached (compile tested only).

Signed-Off-By: Mika Kukkonen <mikukkon@iki.fi>

diff --git a/fs/afs/write.c b/fs/afs/write.c
index 83ff292..4bca263 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -395,8 +395,9 @@ static int afs_write_back_from_locked_page(struct afs_writeback *wb,
 		if (n == 0)
 			goto no_more;
 		if (pages[0]->index != start) {
-			for (n--; n >= 0; n--)
+			for (n--; n > 0; n--)
 				put_page(pages[n]);
+			put_page(pages[0]);
 			goto no_more;
 		}

Re: [PATCH] Bug in fs/afs/write.c function afs_write_back_from_locked_page()

[David Howells]

How about the attached instead?

David
---
AFS: Fix interminable loop in afs_write_back_from_locked_page()

From: Mika Kukkonen <mikukkon@miku.homelinux.net>

Following bug was uncovered by compiling with '-W' flag:

  CC [M]  fs/afs/write.o
fs/afs/write.c: In function ‘afs_write_back_from_locked_page’:
fs/afs/write.c:398: warning: comparison of unsigned expression >= 0 is always true

Loop variable 'n' is unsigned, so wraps around happily as far as I can
see. Trival fix attached (compile tested only).

Signed-Off-By: Mika Kukkonen <mikukkon@iki.fi>
Signed-off-by: David Howells <dhowells@redhat.com>
---

 fs/afs/write.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/afs/write.c b/fs/afs/write.c
index 67ae4db..c26d5e8 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -395,8 +395,10 @@ static int afs_write_back_from_locked_page(struct afs_writeback *wb,
 		if (n == 0)
 			goto no_more;
 		if (pages[0]->index != start) {
-			for (n--; n >= 0; n--)
-				put_page(pages[n]);
+			do {
+				put_page(pages[--n]);
+			} while (n > 0);
+			put_page(pages[0]);
 			goto no_more;
 		}
 

Re: [PATCH] Bug in fs/afs/write.c function afs_write_back_from_locked_page()

[David Howells]

David Howells <dhowells@redhat.com> wrote:

> How about the attached instead?

Blech.  How about this instead?  I forgot to remove the extra put_page() you
added.

David
---
AFS: Fix interminable loop in afs_write_back_from_locked_page()

From: Mika Kukkonen <mikukkon@miku.homelinux.net>

Following bug was uncovered by compiling with '-W' flag:

  CC [M]  fs/afs/write.o
fs/afs/write.c: In function ‘afs_write_back_from_locked_page’:
fs/afs/write.c:398: warning: comparison of unsigned expression >= 0 is always true

Loop variable 'n' is unsigned, so wraps around happily as far as I can
see. Trival fix attached (compile tested only).

Signed-Off-By: Mika Kukkonen <mikukkon@iki.fi>
Signed-off-by: David Howells <dhowells@redhat.com>
---

 fs/afs/write.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/afs/write.c b/fs/afs/write.c
index 67ae4db..28f3751 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -395,8 +395,9 @@ static int afs_write_back_from_locked_page(struct afs_writeback *wb,
 		if (n == 0)
 			goto no_more;
 		if (pages[0]->index != start) {
-			for (n--; n >= 0; n--)
-				put_page(pages[n]);
+			do {
+				put_page(pages[--n]);
+			} while (n > 0);
 			goto no_more;
 		}