From: "Gustavo A. R. Silva" <gustavoars@kernel.org>
To: David Sterba <dsterba@suse.com>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: [PATCH] btrfs: add special case to setget helpers for 64k pages
Date: Thu, 1 Jul 2021 16:57:40 -0500 [thread overview]
Message-ID: <20210701215740.GA12099@embeddedor> (raw)
In-Reply-To: <20210701160039.12518-1-dsterba@suse.com>
On Thu, Jul 01, 2021 at 06:00:39PM +0200, David Sterba wrote:
> On 64K pages the size of the extent_buffer::pages array is 1 and
> compilation with -Warray-bounds warns due to
>
> kaddr = page_address(eb->pages[idx + 1]);
>
> when reading byte range crossing page boundary.
>
> This does never actually overflow the array because on 64K because all
> the data fit in one page and bounds are checked by check_setget_bounds.
>
> To fix the reported overflow and warning add a copy of the non-crossing
> read/write code and put it behind a condition that's evaluated at
> compile time. That way only one implementation remains due to dead code
> elimination.
Any chance we can use a flexible-array in struct extent_buffer instead,
so all the warnings are removed?
Something like this:
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 62027f551b44..b82e8b694a3b 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -94,11 +94,11 @@ struct extent_buffer {
struct rw_semaphore lock;
- struct page *pages[INLINE_EXTENT_BUFFER_PAGES];
struct list_head release_list;
#ifdef CONFIG_BTRFS_DEBUG
struct list_head leak_list;
#endif
+ struct page *pages[];
};
/*
which is actually what is needed in this case to silence the
array-bounds warnings: the replacement of the one-element array
with a flexible-array member[1] in struct extent_buffer.
--
Gustavo
[1] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays
>
> Link: https://lore.kernel.org/lkml/20210623083901.1d49d19d@canb.auug.org.au/
> CC: Gustavo A. R. Silva <gustavoars@kernel.org>
> Signed-off-by: David Sterba <dsterba@suse.com>
> ---
> fs/btrfs/struct-funcs.c | 66 +++++++++++++++++++++++++----------------
> 1 file changed, 41 insertions(+), 25 deletions(-)
>
> diff --git a/fs/btrfs/struct-funcs.c b/fs/btrfs/struct-funcs.c
> index 8260f8bb3ff0..51204b280da8 100644
> --- a/fs/btrfs/struct-funcs.c
> +++ b/fs/btrfs/struct-funcs.c
> @@ -73,14 +73,18 @@ u##bits btrfs_get_token_##bits(struct btrfs_map_token *token, \
> } \
> token->kaddr = page_address(token->eb->pages[idx]); \
> token->offset = idx << PAGE_SHIFT; \
> - if (oip + size <= PAGE_SIZE) \
> + if (INLINE_EXTENT_BUFFER_PAGES == 1) { \
> return get_unaligned_le##bits(token->kaddr + oip); \
> + } else { \
> + if (oip + size <= PAGE_SIZE) \
> + return get_unaligned_le##bits(token->kaddr + oip); \
> \
> - memcpy(lebytes, token->kaddr + oip, part); \
> - token->kaddr = page_address(token->eb->pages[idx + 1]); \
> - token->offset = (idx + 1) << PAGE_SHIFT; \
> - memcpy(lebytes + part, token->kaddr, size - part); \
> - return get_unaligned_le##bits(lebytes); \
> + memcpy(lebytes, token->kaddr + oip, part); \
> + token->kaddr = page_address(token->eb->pages[idx + 1]); \
> + token->offset = (idx + 1) << PAGE_SHIFT; \
> + memcpy(lebytes + part, token->kaddr, size - part); \
> + return get_unaligned_le##bits(lebytes); \
> + } \
> } \
> u##bits btrfs_get_##bits(const struct extent_buffer *eb, \
> const void *ptr, unsigned long off) \
> @@ -94,13 +98,17 @@ u##bits btrfs_get_##bits(const struct extent_buffer *eb, \
> u8 lebytes[sizeof(u##bits)]; \
> \
> ASSERT(check_setget_bounds(eb, ptr, off, size)); \
> - if (oip + size <= PAGE_SIZE) \
> + if (INLINE_EXTENT_BUFFER_PAGES == 1) { \
> return get_unaligned_le##bits(kaddr + oip); \
> + } else { \
> + if (oip + size <= PAGE_SIZE) \
> + return get_unaligned_le##bits(kaddr + oip); \
> \
> - memcpy(lebytes, kaddr + oip, part); \
> - kaddr = page_address(eb->pages[idx + 1]); \
> - memcpy(lebytes + part, kaddr, size - part); \
> - return get_unaligned_le##bits(lebytes); \
> + memcpy(lebytes, kaddr + oip, part); \
> + kaddr = page_address(eb->pages[idx + 1]); \
> + memcpy(lebytes + part, kaddr, size - part); \
> + return get_unaligned_le##bits(lebytes); \
> + } \
> } \
> void btrfs_set_token_##bits(struct btrfs_map_token *token, \
> const void *ptr, unsigned long off, \
> @@ -124,15 +132,19 @@ void btrfs_set_token_##bits(struct btrfs_map_token *token, \
> } \
> token->kaddr = page_address(token->eb->pages[idx]); \
> token->offset = idx << PAGE_SHIFT; \
> - if (oip + size <= PAGE_SIZE) { \
> + if (INLINE_EXTENT_BUFFER_PAGES == 1) { \
> put_unaligned_le##bits(val, token->kaddr + oip); \
> - return; \
> + } else { \
> + if (oip + size <= PAGE_SIZE) { \
> + put_unaligned_le##bits(val, token->kaddr + oip); \
> + return; \
> + } \
> + put_unaligned_le##bits(val, lebytes); \
> + memcpy(token->kaddr + oip, lebytes, part); \
> + token->kaddr = page_address(token->eb->pages[idx + 1]); \
> + token->offset = (idx + 1) << PAGE_SHIFT; \
> + memcpy(token->kaddr, lebytes + part, size - part); \
> } \
> - put_unaligned_le##bits(val, lebytes); \
> - memcpy(token->kaddr + oip, lebytes, part); \
> - token->kaddr = page_address(token->eb->pages[idx + 1]); \
> - token->offset = (idx + 1) << PAGE_SHIFT; \
> - memcpy(token->kaddr, lebytes + part, size - part); \
> } \
> void btrfs_set_##bits(const struct extent_buffer *eb, void *ptr, \
> unsigned long off, u##bits val) \
> @@ -146,15 +158,19 @@ void btrfs_set_##bits(const struct extent_buffer *eb, void *ptr, \
> u8 lebytes[sizeof(u##bits)]; \
> \
> ASSERT(check_setget_bounds(eb, ptr, off, size)); \
> - if (oip + size <= PAGE_SIZE) { \
> + if (INLINE_EXTENT_BUFFER_PAGES == 1) { \
> put_unaligned_le##bits(val, kaddr + oip); \
> - return; \
> - } \
> + } else { \
> + if (oip + size <= PAGE_SIZE) { \
> + put_unaligned_le##bits(val, kaddr + oip); \
> + return; \
> + } \
> \
> - put_unaligned_le##bits(val, lebytes); \
> - memcpy(kaddr + oip, lebytes, part); \
> - kaddr = page_address(eb->pages[idx + 1]); \
> - memcpy(kaddr, lebytes + part, size - part); \
> + put_unaligned_le##bits(val, lebytes); \
> + memcpy(kaddr + oip, lebytes, part); \
> + kaddr = page_address(eb->pages[idx + 1]); \
> + memcpy(kaddr, lebytes + part, size - part); \
> + } \
> }
>
> DEFINE_BTRFS_SETGET_BITS(8)
> --
> 2.31.1
>
next prev parent reply other threads:[~2021-07-01 21:55 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-01 16:00 [PATCH] btrfs: add special case to setget helpers for 64k pages David Sterba
2021-07-01 21:57 ` Gustavo A. R. Silva [this message]
2021-07-01 23:59 ` Qu Wenruo
2021-07-02 0:09 ` Gustavo A. R. Silva
2021-07-02 0:21 ` Qu Wenruo
2021-07-02 0:39 ` Gustavo A. R. Silva
2021-07-02 0:39 ` Qu Wenruo
2021-07-02 1:09 ` Gustavo A. R. Silva
2021-07-02 10:22 ` David Sterba
2021-07-02 7:10 ` Christoph Hellwig
2021-07-02 11:06 ` David Sterba
2021-07-05 8:33 ` Christoph Hellwig
2021-07-08 14:34 ` David Sterba
2021-07-14 23:37 ` Gustavo A. R. Silva
2021-07-28 15:32 ` David Sterba
2021-07-28 16:00 ` David Sterba
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