2022-09-22 03:13:01

by Kees Cook

Subject: [PATCH 04/12] btrfs: send: Proactively round up to kmalloc bucket size

Instead of discovering the kmalloc bucket size _after_ allocation, round
up proactively so the allocation is explicitly made for the full size,
allowing the compiler to correctly reason about the resulting size of
the buffer through the existing __alloc_size() hint.

Cc: [email protected]
Signed-off-by: Kees Cook <[email protected]>
---
fs/btrfs/send.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index e7671afcee4f..d40d65598e8f 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -435,6 +435,11 @@ static int fs_path_ensure_buf(struct fs_path *p, int len)
path_len = p->end - p->start;
old_buf_len = p->buf_len;

+ /*
+ * Allocate to the next largest kmalloc bucket size, to let
+ * the fast path happen most of the time.
+ */
+ len = kmalloc_size_roundup(len);
/*
* First time the inline_buf does not suffice
*/
@@ -448,11 +453,7 @@ static int fs_path_ensure_buf(struct fs_path *p, int len)
if (!tmp_buf)
return -ENOMEM;
p->buf = tmp_buf;
- /*
- * The real size of the buffer is bigger, this will let the fast path
- * happen most of the time
- */
- p->buf_len = ksize(p->buf);
+ p->buf_len = len;

if (p->reversed) {
tmp_buf = p->buf + old_buf_len - path_len - 1;
--
2.34.1

2022-09-22 13:41:53

by David Sterba

Subject: Re: [PATCH 04/12] btrfs: send: Proactively round up to kmalloc bucket size

On Wed, Sep 21, 2022 at 08:10:05PM -0700, Kees Cook wrote:
> Instead of discovering the kmalloc bucket size _after_ allocation, round
> up proactively so the allocation is explicitly made for the full size,
> allowing the compiler to correctly reason about the resulting size of
> the buffer through the existing __alloc_size() hint.
>
> Cc: [email protected]
> Signed-off-by: Kees Cook <[email protected]>

Acked-by: David Sterba <[email protected]>