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mm/mmap.c: use IS_ERR_VALUE to check return value of get_unmapped_area

PATCH In review Gaowei Pu 2 participants 3 messages Oct 12, 2019 – Oct 16, 2019

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Gaowei Pu

author
#0 lore raw

PATCH v2 1/1 mm/mmap.c: use IS_ERR_VALUE to check return value of get_unmapped_area

get_unmapped_area already cover the offset_in_page() check and returned with error ptr. So replace offset_in_page() with IS_ERR_VALUE().

Signed-off-by Gaowei Pu <[email protected]>

V2: fix compile warnning.

---
 mm/mmap.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)
mm/mmap.c +5 -4
index 7e8c3e8ae75f..6aebfeb6a486 100644
@@ -1430,7 +1430,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 	 * that it represents a valid section of the address space.
 	 */
 	addr = get_unmapped_area(file, addr, len, pgoff, flags);
-	if (offset_in_page(addr))
+	if (IS_ERR_VALUE(addr))
 		return addr;
 
 	if (flags & MAP_FIXED_NOREPLACE) {

@@ -2990,15 +2990,16 @@ static int do_brk_flags(unsigned long addr, unsigned long len, unsigned long fla
 	struct rb_node **rb_link, *rb_parent;
 	pgoff_t pgoff = addr >> PAGE_SHIFT;
 	int error;
+	unsigned long mapped_addr;
 
 	/* Until we need other flags, refuse anything except VM_EXEC. */
 	if ((flags & (~VM_EXEC)) != 0)
 		return -EINVAL;
 	flags |= VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;
 
-	error = get_unmapped_area(NULL, addr, len, 0, MAP_FIXED);
-	if (offset_in_page(error))
-		return error;
+	mapped_addr = get_unmapped_area(NULL, addr, len, 0, MAP_FIXED);
+	if (IS_ERR_VALUE(mapped_addr))
+		return mapped_addr;
 
 	error = mlock_future_check(mm, mm->def_flags, len);
 	if (error)
Signature · 1 line
2.23.0
#1 lore raw
Quoted 2 lines · Gaowei Pu

get_unmapped_area already cover the offset_in_page() check and returned with error ptr. So replace offset_in_page() with IS_ERR_VALUE().

I have to say that I found offset_in_page check quite unintuitive. It is a relict from the past I suspect. A newer code seems to use IS_ERR_VALUE. If we want to make the code consistent then I am for it. Could you check other users as well? git grep suggests checking kernel/events/uprobes.c, mm/mmap.c and mm/mremap.c.

I would simply use the following for the changelog
"
get_unmapped_area returns an address or -errno on failure. Historically we have checked for the failure by offset_in_page() which is correct but quite hard to read. Newer code started using IS_ERR_VALUE which is much easier to read. Convert remaining users of offset_in_page as well.

This shouldn't introduce any functional changes.
"

Quoted 43 lines
Signed-off-by Gaowei Pu <[email protected]>

V2: fix compile warnning.

---
 mm/mmap.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)
mm/mmap.c +5 -4
index 7e8c3e8ae75f..6aebfeb6a486 100644
@@ -1430,7 +1430,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 	 * that it represents a valid section of the address space.
 	 */
 	addr = get_unmapped_area(file, addr, len, pgoff, flags);
-	if (offset_in_page(addr))
+	if (IS_ERR_VALUE(addr))
 		return addr;
 
 	if (flags & MAP_FIXED_NOREPLACE) {

@@ -2990,15 +2990,16 @@ static int do_brk_flags(unsigned long addr, unsigned long len, unsigned long fla
 	struct rb_node **rb_link, *rb_parent;
 	pgoff_t pgoff = addr >> PAGE_SHIFT;
 	int error;
+	unsigned long mapped_addr;
 
 	/* Until we need other flags, refuse anything except VM_EXEC. */
 	if ((flags & (~VM_EXEC)) != 0)
 		return -EINVAL;
 	flags |= VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;
 
-	error = get_unmapped_area(NULL, addr, len, 0, MAP_FIXED);
-	if (offset_in_page(error))
-		return error;
+	mapped_addr = get_unmapped_area(NULL, addr, len, 0, MAP_FIXED);
+	if (IS_ERR_VALUE(mapped_addr))
+		return mapped_addr;
 
 	error = mlock_future_check(mm, mm->def_flags, len);
 	if (error)
Signature · 1 line
2.23.0
Signature · 2 lines
Michal Hocko
SUSE Labs
author
#2 lore raw
Quoted 10 lines · Michal Hocko
Quoted 2 lines · Gaowei Pu

get_unmapped_area already cover the offset_in_page() check and returned with error ptr. So replace offset_in_page() with IS_ERR_VALUE().

I have to say that I found offset_in_page check quite unintuitive. It is a relict from the past I suspect. A newer code seems to use IS_ERR_VALUE. If we want to make the code consistent then I am for it. Could you check other users as well? git grep suggests checking kernel/events/uprobes.c, mm/mmap.c and mm/mremap.c.

I only noticed the offset_in_page check after returned from get_unmapped_area is redundant.
So I just replace the places where get_unmapped_area returned. As you mentioned, IS_ERR_VALUE maybe
the newer code to check the error ptr compared to offset_in_page which is really unintuitive and therefore I will
replace them in mm/mmap.c and mm/mremap.c.

Quoted 20 lines

I would simply use the following for the changelog
"
get_unmapped_area returns an address or -errno on failure. Historically we have checked for the failure by offset_in_page() which is correct but quite hard to read. Newer code started using IS_ERR_VALUE which is much easier to read. Convert remaining users of offset_in_page as well.

This shouldn't introduce any functional changes.
"

OK, I will use your changelog and resend a patch. Thanks.

Quoted 2 lines

2.23.0

--
Michal Hocko
SUSE Labs