On 07/13/2014 02:50 PM, Christoph Hellwig wrote:
> pramod.gurav.etc@xxxxxxxxx wrote ...
>> diff --git a/fs/direct-io.c b/fs/direct-io.c
>> index 98040ba388ac..c0a9854d2bc7 100644
>> --- a/fs/direct-io.c
>> +++ b/fs/direct-io.c
>> @@ -910,7 +910,8 @@ static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,
>>
>> while (sdio->block_in_file < sdio->final_block_in_request) {
>> struct page *page;
>> - size_t from, to;
>> + size_t from = 0;
>> + size_t to = 0;
>> page = dio_get_page(dio, sdio, &from, &to);
>> if (IS_ERR(page)) {
>> ret = PTR_ERR(page);
> Looks good to me,
>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
>
> Al, can you pick this up? It's the only warnings in many of my usual
> kernel builds at the moment.
>
<>
Paul Bolle <pebolle@xxxxxxxxxx> wrote ...
<>
> @@ -911,11 +907,15 @@ static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,
> while (sdio->block_in_file < sdio->final_block_in_request) {
> struct page *page;
> size_t from, to;
> - page = dio_get_page(dio, sdio, &from, &to);
> +
> + page = dio_get_page(dio, sdio);
> if (IS_ERR(page)) {
> ret = PTR_ERR(page);
> goto out;
> }
> + from = sdio->head ? 0 : sdio->from;
> + to = (sdio->head == sdio->tail - 1) ? sdio->to : PAGE_SIZE;
> + sdio->head++;
>
> while (from < to) {
> unsigned this_chunk_bytes; /* # of bytes mapped */
<>
This is the wrong fix. GCC is wrong here. As shown by Paul Bolle if
you move the from / to set from dio_get_page() to here the warning goes away.
The minimal fix must use uninitialized_var() in this case. See patch below
But I think the proper fix Is the one Paul Bolle <pebolle@xxxxxxxxxx> sent (above)
----
From: Boaz Harrosh <boaz@xxxxxxxxxxxxx>
Date: Wed, 16 Jul 2014 20:02:29 +0300
Subject: [PATCH] do_direct_IO: Fix compiler warning
MIME-Version: 1.0
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Content-Transfer-Encoding: 8bit
This fixes
../fs/direct-io.c: In function ‘do_blockdev_direct_IO’:
../fs/direct-io.c:1011:12: warning: ‘from’ may be used uninitialized in this function [-Wmaybe-uninitialized]
u = (to - from) >> blkbits;
^
../fs/direct-io.c:1011:12: warning: ‘to’ may be used uninitialized in this function [-Wmaybe-uninitialized]
u = (to - from) >> blkbits;
I use: gcc version 4.8.3 20140624 (Red Hat 4.8.3-1)
GCC is wrong here so we should use the uninitialized_var() macro
and not silence it with = 0;
Signed-off-by: Boaz Harrosh <boaz@xxxxxxxxxxxxx>
---
fs/direct-io.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/direct-io.c b/fs/direct-io.c
index 98040ba..156e6f0 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -910,7 +910,8 @@ static int do_direct_IO(struct dio *dio, struct dio_submit *sdio,
while (sdio->block_in_file < sdio->final_block_in_request) {
struct page *page;
- size_t from, to;
+ size_t uninitialized_var(from), uninitialized_var(to);
+
page = dio_get_page(dio, sdio, &from, &to);
if (IS_ERR(page)) {
ret = PTR_ERR(page);
--
1.9.3
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