Re: [PATCH v2] kernel/resource: Fix locking in request_free_mem_region

Alistair Popple
2021-03-29T01:55:26Z

On Friday, 26 March 2021 4:15:36 PM AEDT Balbir Singh wrote:
> On Fri, Mar 26, 2021 at 12:20:35PM +1100, Alistair Popple wrote:
> > +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)));
>
> is_type is a bad name, are we saying "is" as in boolean question?
> Or is it short for something like intersection_type? I know you've
> just moved the code over :)

Yeah, I'm not a fan of that name either but I was just moving code over and
couldn't come up with anything better :)

It is a boolean question though - it is checking to see if resource *p is the
same type (flags+desc) of region as what is being checked for intersection.

> > +
> > + if (resource_overlaps(p, &res))
> > + 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(&resource_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, &res))
> > - is_type ? type++ : other++;
> > - }
> > + rc = __region_intersects(start, size, flags, desc);
> > read_unlock(&resource_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 +1180,17 @@ struct address_space *iomem_get_mapping(void)
> > return smp_load_acquire(&iomem_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 n,
> > - const char *name, int flags)
> > +static bool request_region_locked(struct resource *parent,
> > + struct resource *res, resource_size_t
start,
> > + resource_size_t n, const char *name, int
flags)
> > {
> > - DECLARE_WAITQUEUE(wait, current);
> > - struct resource *res = alloc_resource(GFP_KERNEL);
> > struct resource *orig_parent = parent;
> > -
> > - if (!res)
> > - return NULL;
> > + DECLARE_WAITQUEUE(wait, current);
>
> This part of the diff looks confusing, do we have a waitqueue and we call
> schedule() within a function called with the lock held?

Good point. schedule() does get called but the lock is dropped first:

if (conflict->flags & flags & IORESOURCE_MUXED) {
add_wait_queue(&muxed_resource_wait, &wait);
write_unlock(&resource_lock);
set_current_state(TASK_UNINTERRUPTIBLE);
schedule();
remove_wait_queue(&muxed_resource_wait, &wait);
write_lock(&resource_lock);
continue;
}

This isn't an issue though as it's only used for request_muxed_region() which
isn't used for the ZONE_DEVICE allocation and by design doesn't search for
free space. Ie. IORESOURCE_MUXED will never be set for
request_free_mem_region().

> >
> > res->name = name;
> > res->start = start;
> > res->end = start + n - 1;
> >
> > - write_lock(&resource_lock);
> > -
> > for (;;) {
> > struct resource *conflict;
> >
> > @@ -1230,16 +1225,39 @@ struct resource * __request_region(struct resource
*parent,
> > write_lock(&resource_lock);
> > continue;
> > }
> > - /* Uhhuh, that didn't work out.. */
> > - free_resource(res);
> > - res = NULL;
> > - break;
> > + return false;
> > }
> > - write_unlock(&resource_lock);
> >
> > if (res && orig_parent == &iomem_resource)
> > revoke_iomem(res);
> >
> > + return true;
> > +}
> > +
> > +/**
> > + * __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 n,
> > + const char *name, int flags)
> > +{
> > + struct resource *res = alloc_resource(GFP_KERNEL);
> > +
> > + if (!res)
> > + return NULL;
> > +
> > + write_lock(&resource_lock);
> > + if (!request_region_locked(parent, res, start, n, name, flags)) {
> > + /* Uhhuh, that didn't work out.. */
> > + free_resource(res);
> > + res = NULL;
> > + }
> > + write_unlock(&resource_lock);
>
> Should the function be called __request_region_locked?

This is the name of original function, so this is just maintaining the
original behaviour by taking the lock and calling the inner function
(request_region_locked) rather than having it coded directly there.

__request_region() is rarely called directly and is mostly called via macros:

include/linux/ioport.h:#define request_region(start,n,name)
__request_region(&ioport_resource, (start), (n), (name), 0)
include/linux/ioport.h:#define request_muxed_region(start,n,name)
__request_region(&ioport_resource, (start), (n), (name), IORESOURCE_MUXED)
include/linux/ioport.h:#define __request_mem_region(start,n,name, excl)
__request_region(&iomem_resource, (start), (n), (name), excl)
include/linux/ioport.h:#define request_mem_region(start,n,name)
__request_region(&iomem_resource, (start), (n), (name), 0)

Thanks,

- Alistair

> > return res;
> > }
> > EXPORT_SYMBOL(__request_region);
> > @@ -1779,26 +1797,50 @@ static struct resource
*__request_free_mem_region(struct device *dev,
> > {
> > resource_size_t end, addr;
> > struct resource *res;
> > + struct region_devres *dr = NULL;
> > +
> > + res = alloc_resource(GFP_KERNEL);
> > + if (!res)
> > + return ERR_PTR(-ENOMEM);
> > +
> > + if (dev) {
> > + dr = devres_alloc(devm_region_release, sizeof(struct
region_devres),
> > + GFP_KERNEL);
> > + if (!dr) {
> > + free_resource(res);
> > + return ERR_PTR(-ENOMEM);
> > + }
> > + }
> >
> > size = ALIGN(size, 1UL << PA_SECTION_SHIFT);
> > end = min_t(unsigned long, base->end, (1UL << MAX_PHYSMEM_BITS) -
1);
> > addr = end - size + 1UL;
> >
> > + write_lock(&resource_lock);
> > for (; addr > size && addr >= base->start; addr -= size) {
> > - if (region_intersects(addr, size, 0, IORES_DESC_NONE) !=
> > + if (__region_intersects(addr, size, 0, IORES_DESC_NONE) !=
> > REGION_DISJOINT)
> > continue;
> >
> > - if (dev)
> > - res = devm_request_mem_region(dev, addr, size,
name);
> > - else
> > - res = request_mem_region(addr, size, name);
> > - if (!res)
> > - return ERR_PTR(-ENOMEM);
> > + if (!request_region_locked(&iomem_resource, res, addr,
> > + size, name, 0))
> > + break;
> > +
> > res->desc = IORES_DESC_DEVICE_PRIVATE_MEMORY;
> > + if (dev) {
> > + dr->parent = &iomem_resource;
> > + dr->start = addr;
> > + dr->n = size;
> > + devres_add(dev, dr);
> > + }
> > +
> > + write_unlock(&resource_lock);
> > return res;
> > }
> >
> > + write_unlock(&resource_lock);
> > + free_resource(res);
> > +
> > return ERR_PTR(-ERANGE);
> > }
> >
>
> Balbir Singh.