ACPI, APEI Fix the return value(==NULL) of acpi_pre_map().

PATCH In review Jin Dongming 2 participants 3 messages Sep 2, 2010 – Sep 3, 2010 ACPI

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Jin Dongming

author

2010-09-02 07:19 UTC #0 lore raw

PATCH 1/2 ACPI, APEI Fix the return value(==NULL) of acpi_pre_map().

acpi_pre_map() is used for remapping the physical address of I/O, so it should be return NULL or remapped virtual address. The problem is that when (paddr - pg_off) equals 0, no matter whether I/O remapping is successful or not, the function returns NULL.

In acpi_pre_map(), after the physical address is remapped successfully, it will check whether the physical address has been added into acpi_iomaps list again.
- If the physical address has been added into acpi_iomaps, the virtual address will be saved in vaddr.
- Otherwise, NULL be saved in vaddr.

So if the physical address is the first time to be remapped, vaddr will be NULL always.

In many cases, (paddr - pg_off) may not equal 0. So the function could work well. In our machine, (paddr - pg_off) equals 0, so the return value of acpi_pre_map() is NULL.

This patch fixed it and I confirmed it on x86_64 next-tree.

v2:
Modified the unsuitable description of patch.

v3:
Modified the wrong words in the description of patch.

Signed-off-by Jin Dongming <[email protected]>

Acked-by Huang Ying <[email protected]>

---
 drivers/acpi/atomicio.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

drivers/acpi/atomicio.c +2 -2

index 8f8bd73..1bc2614 100644
@@ -133,7 +133,7 @@ static void __iomem *acpi_pre_map(phys_addr_t paddr,
 
 	spin_lock_irqsave(&acpi_iomaps_lock, flags);
 	vaddr = __acpi_try_ioremap(paddr, size);
-	if (vaddr) {
+	if (unlikely(vaddr)) {
 		spin_unlock_irqrestore(&acpi_iomaps_lock, flags);
 		iounmap(map->vaddr);
 		kfree(map);

@@ -142,7 +142,7 @@ static void __iomem *acpi_pre_map(phys_addr_t paddr,
 	list_add_tail_rcu(&map->list, &acpi_iomaps);
 	spin_unlock_irqrestore(&acpi_iomaps_lock, flags);
 
-	return vaddr + (paddr - pg_off);
+	return map->vaddr + (paddr - pg_off);
 err_unmap:
 	iounmap(vaddr);
 	return NULL;

-- 1.7.1.

Bjorn Helgaas

2010-09-02 15:48 UTC #1 lore raw

Quoted 12 lines · Jin Dongming

acpi_pre_map() is used for remapping the physical address of I/O, so it should be return NULL or remapped virtual address. The problem is that when (paddr - pg_off) equals 0, no matter whether I/O remapping is successful or not, the function returns NULL.
In acpi_pre_map(), after the physical address is remapped successfully, it will check whether the physical address has been added into acpi_iomaps list again.
- If the physical address has been added into acpi_iomaps, the virtual address will be saved in vaddr.
- Otherwise, NULL be saved in vaddr.

Quoted 8 lines

So if the physical address is the first time to be remapped, vaddr will be NULL always.
In many cases, (paddr - pg_off) may not equal 0. So the function could work well. In our machine, (paddr - pg_off) equals 0, so the return value of acpi_pre_map() is NULL.
This patch fixed it and I confirmed it on x86_64 next-tree.

This description is complicated and obscures the very simple bug you are fixing. I suggest something like this:

ACPI: fix acpi_pre_map() return value

After we ioremap() a new region, we call __acpi_try_ioremap() to see whether another thread has already mapped the same region. This check clobbers "vaddr", so compute the return value using the ioremap() result "map->vaddr" instead.

Quoted 17 lines

v2:
Modified the unsuitable description of patch.
v3:
Modified the wrong words in the description of patch.
Signed-off-by Jin Dongming <[email protected]>
Acked-by Huang Ying <[email protected]>
---
 drivers/acpi/atomicio.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
drivers/acpi/atomicio.c +0 -0
index 8f8bd73..1bc2614 100644

drivers/acpi/atomicio.c static void __iomem *acpi_pre_map(phys_addr_t paddr, · line 136

Quoted 5 lines

drivers/acpi/atomicio.c +1 -1

@@ -133,7 +133,7 @@ static void __iomem *acpi_pre_map(phys_addr_t paddr,
 
 	spin_lock_irqsave(&acpi_iomaps_lock, flags);
 	vaddr = __acpi_try_ioremap(paddr, size);
-	if (vaddr) {
+	if (unlikely(vaddr)) {

This "unlikely" addition also obscures things. It's completely unrelated to the bug you're fixing, so it should be in a different patch, and I'm dubious that there's enough performance advantage to compensate for the decreased code readability. I wouldn't make this change unless you can measure a performance improvement.

drivers/acpi/atomicio.c static void __iomem *acpi_pre_map(phys_addr_t paddr, · line 145

Quoted 9 lines

drivers/acpi/atomicio.c +1 -1

 		spin_unlock_irqrestore(&acpi_iomaps_lock, flags);
 		iounmap(map->vaddr);
 		kfree(map);

@@ -142,7 +142,7 @@ static void __iomem *acpi_pre_map(phys_addr_t paddr,
 	list_add_tail_rcu(&map->list, &acpi_iomaps);
 	spin_unlock_irqrestore(&acpi_iomaps_lock, flags);
 
-	return vaddr + (paddr - pg_off);
+	return map->vaddr + (paddr - pg_off);

Since you're changing this line anyway, I think you should change it to:

  return map->vaddr + (paddr - map->paddr);

so it matches __acpi_try_ioremap().

Quoted 10 lines

drivers/acpi/atomicio.c +0 -2
 err_unmap:
 	iounmap(vaddr);
 	return NULL;
-- 1.7.1.
 
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Jin Dongming

author

2010-09-03 08:36 UTC #2 lore raw

Hi, Bjorn Helgaas

I will modify this patch and resend it as soon as possible in next week.

Best Regards,
Jin Dongming

Quoted 94 lines · Bjorn Helgaas

Quoted 12 lines · Jin Dongming
acpi_pre_map() is used for remapping the physical address of I/O, so it should be return NULL or remapped virtual address. The problem is that when (paddr - pg_off) equals 0, no matter whether I/O remapping is successful or not, the function returns NULL.
In acpi_pre_map(), after the physical address is remapped successfully, it will check whether the physical address has been added into acpi_iomaps list again.
- If the physical address has been added into acpi_iomaps, the virtual address will be saved in vaddr.
- Otherwise, NULL be saved in vaddr.
Quoted 8 lines
So if the physical address is the first time to be remapped, vaddr will be NULL always.
In many cases, (paddr - pg_off) may not equal 0. So the function could work well. In our machine, (paddr - pg_off) equals 0, so the return value of acpi_pre_map() is NULL.
This patch fixed it and I confirmed it on x86_64 next-tree.
This description is complicated and obscures the very simple bug you are fixing. I suggest something like this:
ACPI: fix acpi_pre_map() return value
After we ioremap() a new region, we call __acpi_try_ioremap() to see whether another thread has already mapped the same region. This check clobbers "vaddr", so compute the return value using the ioremap() result "map->vaddr" instead.
Quoted 17 lines
v2:
Modified the unsuitable description of patch.
v3:
Modified the wrong words in the description of patch.
Signed-off-by Jin Dongming <[email protected]>
Acked-by Huang Ying <[email protected]>
---
 drivers/acpi/atomicio.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
drivers/acpi/atomicio.c +0 -0
index 8f8bd73..1bc2614 100644
drivers/acpi/atomicio.c static void __iomem *acpi_pre_map(phys_addr_t paddr, · line 136
Quoted 5 lines
drivers/acpi/atomicio.c +1 -1
@@ -133,7 +133,7 @@ static void __iomem *acpi_pre_map(phys_addr_t paddr,
 
 	spin_lock_irqsave(&acpi_iomaps_lock, flags);
 	vaddr = __acpi_try_ioremap(paddr, size);
-	if (vaddr) {
+	if (unlikely(vaddr)) {
This "unlikely" addition also obscures things. It's completely unrelated to the bug you're fixing, so it should be in a different patch, and I'm dubious that there's enough performance advantage to compensate for the decreased code readability. I wouldn't make this change unless you can measure a performance improvement.
drivers/acpi/atomicio.c static void __iomem *acpi_pre_map(phys_addr_t paddr, · line 145
Quoted 9 lines
drivers/acpi/atomicio.c +1 -1
 		spin_unlock_irqrestore(&acpi_iomaps_lock, flags);
 		iounmap(map->vaddr);
 		kfree(map);
@@ -142,7 +142,7 @@ static void __iomem *acpi_pre_map(phys_addr_t paddr,
 	list_add_tail_rcu(&map->list, &acpi_iomaps);
 	spin_unlock_irqrestore(&acpi_iomaps_lock, flags);
 
-	return vaddr + (paddr - pg_off);
+	return map->vaddr + (paddr - pg_off);
Since you're changing this line anyway, I think you should change it to:
  return map->vaddr + (paddr - map->paddr);
so it matches __acpi_try_ioremap().
Quoted 10 lines
drivers/acpi/atomicio.c +0 -2
 err_unmap:
 	iounmap(vaddr);
 	return NULL;
-- 1.7.1.
 
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