fs/direct-io.c: Fix compilation warning for uninitialized variables

Looks good to me,

Reviewed-by Christoph Hellwig <[email protected]>

Al, can you pick this up? It's the only warnings in many of my usual kernel builds at the moment.

[email protected] wrote ...

Quoted 5 lines

fs/direct-io.c +0 -0

index 98040ba388ac..c0a9854d2bc7 100644

fs/direct-io.c static int do_direct_IO(struct dio *dio, struct dio_submit *sdio, · line 917

Quoted 9 lines

fs/direct-io.c +2 -1

@@ -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 <[email protected]>

Al, can you pick this up? It's the only warnings in many of my usual kernel builds at the moment.

(quoted diff) +2 -1

@@ -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);

Quoted 17 lines · Christoph Hellwig

[email protected] wrote ...

Quoted 5 lines

fs/direct-io.c +0 -0

index 98040ba388ac..c0a9854d2bc7 100644

fs/direct-io.c static int do_direct_IO(struct dio *dio, struct dio_submit *sdio, · line 917

Quoted 9 lines

fs/direct-io.c +2 -1

@@ -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,

Quoted 5 lines

Reviewed-by Christoph Hellwig <[email protected]>

Al, can you pick this up? It's the only warnings in many of my usual kernel builds at the moment.

<>

Paul Bolle <[email protected]> wrote ...
<>

Quoted 15 lines

(quoted diff) +5 -1

@@ -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++;
 

Review static int do_direct_IO(struct dio *dio, struct dio_submit *sdio, · line 921

Quoted 2 lines

(quoted diff) +0 -0

 		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 <[email protected]> sent (above)

----
From: Boaz Harrosh <[email protected]>
Date: Wed, 16 Jul 2014 20:02:29 +0300
Subject: [PATCH] do_direct_IO: Fix compiler warning
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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 <[email protected]>

---
 fs/direct-io.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

fs/direct-io.c +2 -1

index 98040ba..156e6f0 100644
@@ -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);

Signature · 1 line

1.9.3

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 <[email protected]> sent (above)

Quoted 6 lines

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 <[email protected]> sent (above)

I don't think the initialization is wrong. The fix of moving the code defintively looks nicer,

while I think uninitialized_var is horrible wart

that won't get anywhere near my code.

Either way we should merge one of those fixes ASAP..

From: Paul Bolle <[email protected]>

The following warnings:

fs/direct-io.c: In function ‘__blockdev_direct_IO’:
fs/direct-io.c:1011:12: warning: ‘to’ may be used uninitialized in this function [-Wmaybe-uninitialized] fs/direct-io.c:913:16: note: ‘to’ was declared here
fs/direct-io.c:1011:12: warning: ‘from’ may be used uninitialized in this function [-Wmaybe-uninitialized] fs/direct-io.c:913:10: note: ‘from’ was declared here

are false positive because dio_get_page() either fails, or sets both 'from' and 'to'.

Maybe it's better to move initializing "to" and "from" out of dio_get_page(). That _might_ make it easier for both the the reader and the compiler to understand what's going on. Something like this:

Christoph Hellwig said ...
The fix of moving the code defintively looks nicer, while I think uninitialized_var is horrible wart that won't get anywhere near my code.

Boaz Harrosh I agree with Christoph and Paul

Signed-off-by Paul Bolle <[email protected]>

Signed-off-by Boaz Harrosh <[email protected]>

---
 fs/direct-io.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

fs/direct-io.c +7 -7

index 98040ba..2f024fc 100644
@@ -198,9 +198,8 @@ static inline int dio_refill_pages(struct dio *dio, struct dio_submit *sdio)
  * L1 cache.
  */
 static inline struct page *dio_get_page(struct dio *dio,
-		struct dio_submit *sdio, size_t *from, size_t *to)
+		struct dio_submit *sdio)
 {
-	int n;
 	if (dio_pages_present(sdio) == 0) {
 		int ret;
 

@@ -209,10 +208,7 @@ static inline struct page *dio_get_page(struct dio *dio,
 			return ERR_PTR(ret);
 		BUG_ON(dio_pages_present(sdio) == 0);
 	}
-	n = sdio->head++;
-	*from = n ? 0 : sdio->from;
-	*to = (n == sdio->tail - 1) ? sdio->to : PAGE_SIZE;
-	return dio->pages[n];
+	return dio->pages[sdio->head];
 }
 
 /**

@@ -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 */

Quoted 1 line

Signed-off-by Paul Bolle <[email protected]>

Paul this is your patch I put you as Signed-off-by please acknowledge

From: Paul Bolle <[email protected]>

The following warnings:

fs/direct-io.c: In function ‘__blockdev_direct_IO’:
fs/direct-io.c:1011:12: warning: ‘to’ may be used uninitialized in this function [-Wmaybe-uninitialized] fs/direct-io.c:913:16: note: ‘to’ was declared here
fs/direct-io.c:1011:12: warning: ‘from’ may be used uninitialized in this function [-Wmaybe-uninitialized] fs/direct-io.c:913:10: note: ‘from’ was declared here

are false positive because dio_get_page() either fails, or sets both 'from' and 'to'.

Maybe it's better to move initializing "to" and "from" out of dio_get_page(). That _might_ make it easier for both the the reader and the compiler to understand what's going on. Something like this:

Christoph Hellwig said ...
The fix of moving the code defintively looks nicer, while I think uninitialized_var is horrible wart that won't get anywhere near my code.

Boaz Harrosh I agree with Christoph and Paul

Signed-off-by Paul Bolle <[email protected]>

Signed-off-by Boaz Harrosh <[email protected]>

---
 fs/direct-io.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

fs/direct-io.c +4 -7

index 98040ba..2f024fc 100644
@@ -198,9 +198,8 @@ static inline int dio_refill_pages(struct dio *dio, struct dio_submit *sdio)
  * L1 cache.
  */
 static inline struct page *dio_get_page(struct dio *dio,
-		struct dio_submit *sdio, size_t *from, size_t *to)
+		struct dio_submit *sdio)
 {
-	int n;
 	if (dio_pages_present(sdio) == 0) {
 		int ret;
 

@@ -209,10 +208,7 @@ static inline struct page *dio_get_page(struct dio *dio,
 			return ERR_PTR(ret);
 		BUG_ON(dio_pages_present(sdio) == 0);
 	}
-	n = sdio->head++;
-	*from = n ? 0 : sdio->from;
-	*to = (n == sdio->tail - 1) ? sdio->to : PAGE_SIZE;
-	return dio->pages[n];
+	return dio->pages[sdio->head];
 }
 
 /**

@@ -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);

Boaz,

Quoted 21 lines · Boaz Harrosh

From: Paul Bolle <[email protected]>

The following warnings:

fs/direct-io.c: In function ‘__blockdev_direct_IO’:
fs/direct-io.c:1011:12: warning: ‘to’ may be used uninitialized in this function [-Wmaybe-uninitialized] fs/direct-io.c:913:16: note: ‘to’ was declared here
fs/direct-io.c:1011:12: warning: ‘from’ may be used uninitialized in this function [-Wmaybe-uninitialized] fs/direct-io.c:913:10: note: ‘from’ was declared here

are false positive because dio_get_page() either fails, or sets both 'from' and 'to'.

Maybe it's better to move initializing "to" and "from" out of dio_get_page(). That _might_ make it easier for both the the reader and the compiler to understand what's going on. Something like this:

Christoph Hellwig said ...
The fix of moving the code defintively looks nicer, while I think uninitialized_var is horrible wart that won't get anywhere near my code.

Quoted 3 lines

Boaz Harrosh I agree with Christoph and Paul

Signed-off-by Paul Bolle <[email protected]>

This is simply not coorect!

Quoted 40 lines

Signed-off-by Boaz Harrosh <[email protected]>

---
 fs/direct-io.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

fs/direct-io.c +4 -7

index 98040ba..2f024fc 100644
@@ -198,9 +198,8 @@ static inline int dio_refill_pages(struct dio *dio, struct dio_submit *sdio)
  * L1 cache.
  */
 static inline struct page *dio_get_page(struct dio *dio,
-		struct dio_submit *sdio, size_t *from, size_t *to)
+		struct dio_submit *sdio)
 {
-	int n;
 	if (dio_pages_present(sdio) == 0) {
 		int ret;
 

@@ -209,10 +208,7 @@ static inline struct page *dio_get_page(struct dio *dio,
 			return ERR_PTR(ret);
 		BUG_ON(dio_pages_present(sdio) == 0);
 	}
-	n = sdio->head++;
-	*from = n ? 0 : sdio->from;
-	*to = (n == sdio->tail - 1) ? sdio->to : PAGE_SIZE;
-	return dio->pages[n];
+	return dio->pages[sdio->head];
 }
 
 /**

@@ -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);

fs/direct-io.c static int do_direct_IO(struct dio *dio, struct dio_submit *sdio, · line 921

Quoted 10 lines

fs/direct-io.c +3 -0

 		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 */

Paul Bolle

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From: Paul Bolle <[email protected]>

Looks good to me,

Reviewed-by Christoph Hellwig <[email protected]>

While it looks obvious, did you make sure it passes xfstests, which has a lot of direct I/O tests?