* [PATCH v2] f2fs: replace a build-time warning with runtime WARN_ON
@ 2016-10-27 15:32 Arnd Bergmann
2016-11-02 7:09 ` Chao Yu
0 siblings, 1 reply; 3+ messages in thread
From: Arnd Bergmann @ 2016-10-27 15:32 UTC (permalink / raw)
To: Jaegeuk Kim, Chao Yu
Cc: Arnd Bergmann, Fan Li, Weichao Guo, linux-f2fs-devel, linux-kernel
gcc is unsure about the use of last_ofs_in_node, which might happen
without a prior initialization:
fs/f2fs//git/arm-soc/fs/f2fs/data.c: In function ‘f2fs_map_blocks’:
fs/f2fs/data.c:799:54: warning: ‘last_ofs_in_node’ may be used uninitialized in this function [-Wmaybe-uninitialized]
if (prealloc && dn.ofs_in_node != last_ofs_in_node + 1) {
As pointed out by Chao Yu, the code is actually correct as 'prealloc'
is only set if the last_ofs_in_node has been set, the two always
get updated together.
This initializes last_ofs_in_node to dn.ofs_in_node for each
new dnode at the start of the 'next_block' loop, which at that
point is a correct initialization as well. I assume that compilers
that correctly track the contents of the variables and do not
warn about the condition also figure out that they can eliminate
the extra assignment here.
Fixes: 46008c6d4232 ("f2fs: support in batch multi blocks preallocation")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
fs/f2fs/data.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
v2: use simpler workaround, as discussed with Chao Yu.
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 68edb47f5f71..cf5ec39f907d 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -713,7 +713,7 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map,
}
prealloc = 0;
- ofs_in_node = dn.ofs_in_node;
+ last_ofs_in_node = ofs_in_node = dn.ofs_in_node;
end_offset = ADDRS_PER_PAGE(dn.node_page, inode);
next_block:
--
2.9.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v2] f2fs: replace a build-time warning with runtime WARN_ON
2016-10-27 15:32 [PATCH v2] f2fs: replace a build-time warning with runtime WARN_ON Arnd Bergmann
@ 2016-11-02 7:09 ` Chao Yu
2016-11-02 13:53 ` Arnd Bergmann
0 siblings, 1 reply; 3+ messages in thread
From: Chao Yu @ 2016-11-02 7:09 UTC (permalink / raw)
To: Arnd Bergmann, Jaegeuk Kim
Cc: Fan Li, Weichao Guo, linux-f2fs-devel, linux-kernel
Hi Arnd, Jaegeuk,
It is trivial, but it's better keep commit *title*, commit log and code
consistent. :)
Thanks,
On 2016/10/27 23:32, Arnd Bergmann wrote:
> gcc is unsure about the use of last_ofs_in_node, which might happen
> without a prior initialization:
>
> fs/f2fs//git/arm-soc/fs/f2fs/data.c: In function ‘f2fs_map_blocks’:
> fs/f2fs/data.c:799:54: warning: ‘last_ofs_in_node’ may be used uninitialized in this function [-Wmaybe-uninitialized]
> if (prealloc && dn.ofs_in_node != last_ofs_in_node + 1) {
>
> As pointed out by Chao Yu, the code is actually correct as 'prealloc'
> is only set if the last_ofs_in_node has been set, the two always
> get updated together.
>
> This initializes last_ofs_in_node to dn.ofs_in_node for each
> new dnode at the start of the 'next_block' loop, which at that
> point is a correct initialization as well. I assume that compilers
> that correctly track the contents of the variables and do not
> warn about the condition also figure out that they can eliminate
> the extra assignment here.
>
> Fixes: 46008c6d4232 ("f2fs: support in batch multi blocks preallocation")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> fs/f2fs/data.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> v2: use simpler workaround, as discussed with Chao Yu.
>
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 68edb47f5f71..cf5ec39f907d 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -713,7 +713,7 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map,
> }
>
> prealloc = 0;
> - ofs_in_node = dn.ofs_in_node;
> + last_ofs_in_node = ofs_in_node = dn.ofs_in_node;
> end_offset = ADDRS_PER_PAGE(dn.node_page, inode);
>
> next_block:
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v2] f2fs: replace a build-time warning with runtime WARN_ON
2016-11-02 7:09 ` Chao Yu
@ 2016-11-02 13:53 ` Arnd Bergmann
0 siblings, 0 replies; 3+ messages in thread
From: Arnd Bergmann @ 2016-11-02 13:53 UTC (permalink / raw)
To: Chao Yu; +Cc: Jaegeuk Kim, Fan Li, Weichao Guo, linux-f2fs-devel, linux-kernel
On Wednesday 02 November 2016, Chao Yu wrote:
> Hi Arnd, Jaegeuk,
>
> It is trivial, but it's better keep commit *title*, commit log and code
> consistent. :)
Sorry for my silly mistake, sent it again with a new subject now.
Arnd
^ permalink raw reply [flat|nested] 3+ messages in thread
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2016-10-27 15:32 [PATCH v2] f2fs: replace a build-time warning with runtime WARN_ON Arnd Bergmann
2016-11-02 7:09 ` Chao Yu
2016-11-02 13:53 ` Arnd Bergmann
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