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SubjectRe: [PATCH v3] perf, x86: Fix multi-segment problem of perf_event_intel_uncore
On Fri, Sep 04, 2015 at 02:28:36AM +0900, Taku Izumi wrote:

> +struct pci2phy_map *__find_pci2phy_map(int segment)
> +{
> + struct pci2phy_map *map;
> +
> + lockdep_assert_held(&pci2phy_map_lock);
> +
> + list_for_each_entry(map, &pci2phy_map_head, list) {
> + if (map->segment == segment)
> + return map;
> + }
> +
> + map = kmalloc(sizeof(struct pci2phy_map), GFP_ATOMIC);

So Ingo would really rather you didn't add a GFP_ATOMIC here; they are
rather fragile.

http://lkml.kernel.org/r/20150901113147.GA11161@gmail.com

I figured you'd come up with something... :/

> + if (map) {
> + map->segment = segment;
> + list_add_tail(&map->list, &pci2phy_map_head);
> + }
> +
> + return map;
> +}


Something like this might work; but please consider it carefully,
because I certainly didn't.

struct pci2phy_map *__find_pci2phy_map(int segment)
{
struct pci2phy_map *map, *alloc = NULL;

lockdep_assert_held(&pci2phy_map_lock);

retry:
list_for_each_entry(map, &pci2phy_map_head, list) {
if (map->segment == segment)
goto done;
}

if (!alloc) {
raw_spin_unlock(&pci2phy_map_lock);
alloc = kmalloc(sizeof(struct pci2phy_map), GFP_KERNEL);
raw_spin_lock(&pci2phy_map_lock);

if (alloc)
goto retry;

return NULL;
} else {
map = alloc;
alloc = NULL;
}

map->segment = segment;
list_add_tail(&map->list, &pci2phy_map_head);

done:
if (alloc)
kfree(alloc);

return map;
}


> @@ -1106,16 +1107,26 @@ static int snbep_pci2phy_map_init(int devid)
> err = pci_read_config_dword(ubox_dev, 0x54, &config);
> if (err)
> break;
> +
> + segment = pci_domain_nr(ubox_dev->bus);
> + raw_spin_lock(&pci2phy_map_lock);
> + map = __find_pci2phy_map(segment);
> + if (!map) {
> + err = -ENOMEM;
> + break;

And here you leak the lock..

> + }
> +
> /*
> * every three bits in the Node ID mapping register maps
> * to a particular node.
> */
> for (i = 0; i < 8; i++) {
> if (nodeid == ((config >> (3 * i)) & 0x7)) {
> - uncore_pcibus_to_physid[bus] = i;
> + map->pbus_to_physid[bus] = i;
> break;
> }
> }
> + raw_spin_unlock(&pci2phy_map_lock);
> }


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