Re: [PATCH v3] kernel/resource: Fix locking in request_free_mem_region
On 3/29/21 9:59 PM, Alistair Popple wrote:
...
res->desc = IORES_DESC_DEVICE_PRIVATE_MEMORY;
+ if (dev) {
+ dr->parent = _resource;
+ dr->start = addr;
+ dr->n = size;
+ devres_add(dev, dr);
+ }
+
+ write_unlock(_lock);
+ revoke_iomem(res);
This is new, and not mentioned in the commit log, and therefore quite
surprising. It seems like the right thing to do but it also seems like a
different fix! I'm not saying that it should be a separate patch, but it
does seem worth loudly mentioning in the commit log, yes?
This isn't a different fix though, it is just about maintaining the original
behaviour which called revoke_iomem() after dropping the lock. I inadvertently
switched this around in the initial patch such that revoke_iomem() got called
with the lock, leading to deadlock on x86 with CONFIG_IO_STRICT_DEVMEM=y.
This does change the order of revoke_iomem() and devres_add() slightly, but as
far as I can tell that shouldn't be an issue. Can call that out in the commit
log.
Maybe that's why it looked like a change to me. I do think it's worth
mentioning.
thanks,
--
John Hubbard
NVIDIA
Re: [PATCH v3] kernel/resource: Fix locking in request_free_mem_region
On Tuesday, 30 March 2021 2:42:34 PM AEDT John Hubbard wrote:
> On 3/29/21 5:38 PM, Alistair Popple wrote:
> > request_free_mem_region() is used to find an empty range of physical
> > addresses for hotplugging ZONE_DEVICE memory. It does this by iterating
> > over the range of possible addresses using region_intersects() to see if
> > the range is free.
> >
> > region_intersects() obtains a read lock before walking the resource tree
> > to protect against concurrent changes. However it drops the lock prior
> > to returning. This means by the time request_mem_region() is called in
> > request_free_mem_region() another thread may have already reserved the
> > requested region resulting in unexpected failures and a message in the
> > kernel log from hitting this condition:
> >
> > /*
> > * mm/hmm.c reserves physical addresses which then
> > * become unavailable to other users. Conflicts are
> > * not expected. Warn to aid debugging if encountered.
> > */
> > if (conflict->desc == IORES_DESC_DEVICE_PRIVATE_MEMORY) {
> > pr_warn("Unaddressable device %s %pR conflicts with %pR",
> > conflict->name, conflict, res);
> >
> > To fix this create versions of region_intersects() and
> > request_mem_region() that allow the caller to take the appropriate lock
> > such that it may be held over the required calls.
> >
> > Instead of creating another version of devm_request_mem_region() that
> > doesn't take the lock open-code it to allow the caller to pre-allocate
> > the required memory prior to taking the lock.
> >
> > Fixes: 0c385190392d8 ("resource: add a not device managed
request_free_mem_region variant")
> > Fixes: 0092908d16c60 ("mm: factor out a devm_request_free_mem_region
helper")
>
> Hi Alistair!
>
> The above "Fixes:" tag looks wrong to me, because that commit did not create
> the broken locking that this patch fixes. Therefore, I think that particular
line
> should be removed from the commit description.
Right, the last "Fixes:" tag is the origin of the bug but the refactoring into
different functions and files made it non-obvious how this patch was related.
Happy to drop these though.
> Another note below:
>
> > Fixes: 4ef589dc9b10c ("mm/hmm/devmem: device memory hotplug using
ZONE_DEVICE")
> > Signed-off-by: Alistair Popple
> > Acked-by: Balbir Singh
> > Reported-by: kernel test robot
> >
> > ---
> >
> > Hi Andrew,
> >
> > This fixes a boot issue reported by the kernel test robot with the
> > previous version of the patch on x86 with CONFIG_IO_STRICT_DEVMEM=y.
> > This was due to the platform specific implementation of
> > devmem_is_allowed() creating a recursive lock which I missed. I notice
> > you have put v2 in mmtom so apologies for the churn but can you please
> > use this version instead? Thanks.
> >
> > - Alistair
> > ---
> > kernel/resource.c | 142 ++
> > 1 file changed, 92 insertions(+), 50 deletions(-)
> >
> > diff --git a/kernel/resource.c b/kernel/resource.c
> > index 627e61b0c124..7061b9f903ca 100644
> > --- a/kernel/resource.c
> > +++ b/kernel/resource.c
> > @@ -523,6 +523,34 @@ int __weak page_is_ram(unsigned long pfn)
> > }
> > EXPORT_SYMBOL_GPL(page_is_ram);
> >
> > +static int __region_intersects(resource_size_t start, size_t size,
> > + unsigned long flags, unsigned long desc)
> > +{
> > + struct resource res;
> > + int type = 0; int other = 0;
> > + struct resource *p;
> > +
> > + res.start = start;
> > + res.end = start + size - 1;
> > +
> > + for (p = iomem_resource.child; p ; p = p->sibling) {
> > + bool is_type = (((p->flags & flags) == flags) &&
> > + ((desc == IORES_DESC_NONE) ||
> > +(desc == p->desc)));
> > +
> > + if (resource_overlaps(p, ))
> > + is_type ? type++ : other++;
> > + }
> > +
> > + if (type == 0)
> > + return REGION_DISJOINT;
> > +
> > + if (other == 0)
> > + return REGION_INTERSECTS;
> > +
> > + return REGION_MIXED;
> > +}
> > +
> > /**
> >* region_intersects() - determine intersection of region with known
resources
> >* @start: region start address
> > @@ -546,31 +574,12 @@ EXPORT_SYMBOL_GPL(page_is_ram);
> > int region_intersects(resource_size_t start, size_t size, unsigned long
flags,
> > unsigned long desc)
> > {
> > - struct resource res;
> > - int type = 0; int other = 0;
> > - struct resource *p;
> > -
> > - res.start = start;
> > - res.end = start + size - 1;
> > + int rc;
> >
> > read_lock(_lock);
> > - for (p = iomem_resource.child; p ; p = p->sibling) {
> > - bool is_type = (((p->flags & flags) == flags) &&
> > - ((desc == IORES_DESC_NONE) ||
> > -(desc == p->desc)));
> > -
> > - if
Re: [PATCH v3] kernel/resource: Fix locking in request_free_mem_region
On 3/29/21 5:38 PM, Alistair Popple wrote:
request_free_mem_region() is used to find an empty range of physical
addresses for hotplugging ZONE_DEVICE memory. It does this by iterating
over the range of possible addresses using region_intersects() to see if
the range is free.
region_intersects() obtains a read lock before walking the resource tree
to protect against concurrent changes. However it drops the lock prior
to returning. This means by the time request_mem_region() is called in
request_free_mem_region() another thread may have already reserved the
requested region resulting in unexpected failures and a message in the
kernel log from hitting this condition:
/*
* mm/hmm.c reserves physical addresses which then
* become unavailable to other users. Conflicts are
* not expected. Warn to aid debugging if encountered.
*/
if (conflict->desc == IORES_DESC_DEVICE_PRIVATE_MEMORY) {
pr_warn("Unaddressable device %s %pR conflicts with %pR",
conflict->name, conflict, res);
To fix this create versions of region_intersects() and
request_mem_region() that allow the caller to take the appropriate lock
such that it may be held over the required calls.
Instead of creating another version of devm_request_mem_region() that
doesn't take the lock open-code it to allow the caller to pre-allocate
the required memory prior to taking the lock.
Fixes: 0c385190392d8 ("resource: add a not device managed request_free_mem_region
variant")
Fixes: 0092908d16c60 ("mm: factor out a devm_request_free_mem_region helper")
Hi Alistair!
The above "Fixes:" tag looks wrong to me, because that commit did not create
the broken locking that this patch fixes. Therefore, I think that particular
line
should be removed from the commit description.
Another note below:
Fixes: 4ef589dc9b10c ("mm/hmm/devmem: device memory hotplug using ZONE_DEVICE")
Signed-off-by: Alistair Popple
Acked-by: Balbir Singh
Reported-by: kernel test robot
---
Hi Andrew,
This fixes a boot issue reported by the kernel test robot with the
previous version of the patch on x86 with CONFIG_IO_STRICT_DEVMEM=y.
This was due to the platform specific implementation of
devmem_is_allowed() creating a recursive lock which I missed. I notice
you have put v2 in mmtom so apologies for the churn but can you please
use this version instead? Thanks.
- Alistair
---
kernel/resource.c | 142 ++
1 file changed, 92 insertions(+), 50 deletions(-)
diff --git a/kernel/resource.c b/kernel/resource.c
index 627e61b0c124..7061b9f903ca 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -523,6 +523,34 @@ int __weak page_is_ram(unsigned long pfn)
}
EXPORT_SYMBOL_GPL(page_is_ram);
+static int __region_intersects(resource_size_t start, size_t size,
+ unsigned long flags, unsigned long desc)
+{
+ struct resource res;
+ int type = 0; int other = 0;
+ struct resource *p;
+
+ res.start = start;
+ res.end = start + size - 1;
+
+ for (p = iomem_resource.child; p ; p = p->sibling) {
+ bool is_type = (((p->flags & flags) == flags) &&
+ ((desc == IORES_DESC_NONE) ||
+(desc == p->desc)));
+
+ if (resource_overlaps(p, ))
+ is_type ? type++ : other++;
+ }
+
+ if (type == 0)
+ return REGION_DISJOINT;
+
+ if (other == 0)
+ return REGION_INTERSECTS;
+
+ return REGION_MIXED;
+}
+
/**
* region_intersects() - determine intersection of region with known resources
* @start: region start address
@@ -546,31 +574,12 @@ EXPORT_SYMBOL_GPL(page_is_ram);
int region_intersects(resource_size_t start, size_t size, unsigned long flags,
unsigned long desc)
{
- struct resource res;
- int type = 0; int other = 0;
- struct resource *p;
-
- res.start = start;
- res.end = start + size - 1;
+ int rc;
read_lock(_lock);
- for (p = iomem_resource.child; p ; p = p->sibling) {
- bool is_type = (((p->flags & flags) == flags) &&
- ((desc == IORES_DESC_NONE) ||
-(desc == p->desc)));
-
- if (resource_overlaps(p, ))
- is_type ? type++ : other++;
- }
+ rc = __region_intersects(start, size, flags, desc);
read_unlock(_lock);
-
- if (type == 0)
- return REGION_DISJOINT;
-
- if (other == 0)
- return REGION_INTERSECTS;
-
- return REGION_MIXED;
+ return rc;
}
EXPORT_SYMBOL_GPL(region_intersects);
@@ -1171,31 +1180,16 @@ struct address_space *iomem_get_mapping(void)
return smp_load_acquire(_inode)->i_mapping;
}
-/**
- * __request_region - create a new busy resource
[PATCH v3] kernel/resource: Fix locking in request_free_mem_region
request_free_mem_region() is used to find an empty range of physical
addresses for hotplugging ZONE_DEVICE memory. It does this by iterating
over the range of possible addresses using region_intersects() to see if
the range is free.
region_intersects() obtains a read lock before walking the resource tree
to protect against concurrent changes. However it drops the lock prior
to returning. This means by the time request_mem_region() is called in
request_free_mem_region() another thread may have already reserved the
requested region resulting in unexpected failures and a message in the
kernel log from hitting this condition:
/*
* mm/hmm.c reserves physical addresses which then
* become unavailable to other users. Conflicts are
* not expected. Warn to aid debugging if encountered.
*/
if (conflict->desc == IORES_DESC_DEVICE_PRIVATE_MEMORY) {
pr_warn("Unaddressable device %s %pR conflicts with %pR",
conflict->name, conflict, res);
To fix this create versions of region_intersects() and
request_mem_region() that allow the caller to take the appropriate lock
such that it may be held over the required calls.
Instead of creating another version of devm_request_mem_region() that
doesn't take the lock open-code it to allow the caller to pre-allocate
the required memory prior to taking the lock.
Fixes: 0c385190392d8 ("resource: add a not device managed
request_free_mem_region variant")
Fixes: 0092908d16c60 ("mm: factor out a devm_request_free_mem_region helper")
Fixes: 4ef589dc9b10c ("mm/hmm/devmem: device memory hotplug using ZONE_DEVICE")
Signed-off-by: Alistair Popple
Acked-by: Balbir Singh
Reported-by: kernel test robot
---
Hi Andrew,
This fixes a boot issue reported by the kernel test robot with the
previous version of the patch on x86 with CONFIG_IO_STRICT_DEVMEM=y.
This was due to the platform specific implementation of
devmem_is_allowed() creating a recursive lock which I missed. I notice
you have put v2 in mmtom so apologies for the churn but can you please
use this version instead? Thanks.
- Alistair
---
kernel/resource.c | 142 ++
1 file changed, 92 insertions(+), 50 deletions(-)
diff --git a/kernel/resource.c b/kernel/resource.c
index 627e61b0c124..7061b9f903ca 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -523,6 +523,34 @@ int __weak page_is_ram(unsigned long pfn)
}
EXPORT_SYMBOL_GPL(page_is_ram);
+static int __region_intersects(resource_size_t start, size_t size,
+ unsigned long flags, unsigned long desc)
+{
+ struct resource res;
+ int type = 0; int other = 0;
+ struct resource *p;
+
+ res.start = start;
+ res.end = start + size - 1;
+
+ for (p = iomem_resource.child; p ; p = p->sibling) {
+ bool is_type = (((p->flags & flags) == flags) &&
+ ((desc == IORES_DESC_NONE) ||
+(desc == p->desc)));
+
+ if (resource_overlaps(p, ))
+ is_type ? type++ : other++;
+ }
+
+ if (type == 0)
+ return REGION_DISJOINT;
+
+ if (other == 0)
+ return REGION_INTERSECTS;
+
+ return REGION_MIXED;
+}
+
/**
* region_intersects() - determine intersection of region with known resources
* @start: region start address
@@ -546,31 +574,12 @@ EXPORT_SYMBOL_GPL(page_is_ram);
int region_intersects(resource_size_t start, size_t size, unsigned long flags,
unsigned long desc)
{
- struct resource res;
- int type = 0; int other = 0;
- struct resource *p;
-
- res.start = start;
- res.end = start + size - 1;
+ int rc;
read_lock(_lock);
- for (p = iomem_resource.child; p ; p = p->sibling) {
- bool is_type = (((p->flags & flags) == flags) &&
- ((desc == IORES_DESC_NONE) ||
-(desc == p->desc)));
-
- if (resource_overlaps(p, ))
- is_type ? type++ : other++;
- }
+ rc = __region_intersects(start, size, flags, desc);
read_unlock(_lock);
-
- if (type == 0)
- return REGION_DISJOINT;
-
- if (other == 0)
- return REGION_INTERSECTS;
-
- return REGION_MIXED;
+ return rc;
}
EXPORT_SYMBOL_GPL(region_intersects);
@@ -1171,31 +1180,16 @@ struct address_space *iomem_get_mapping(void)
return smp_load_acquire(_inode)->i_mapping;
}
-/**
- * __request_region - create a new busy resource region
- * @parent: parent resource descriptor
- * @start: resource start address
- * @n: resource region size
- * @name: reserving caller's ID string
- * @flags: IO resource flags
- */
-struct resource * __request_region(struct resource *parent,
- resource_size_t start, resource_size_t
