On Mon, Apr 9, 2012 at 10:22 AM, Jiang Liu <liuj97@xxxxxxxxx> wrote:
> Use RCU list to protect mmconfig list from dynamic change
> when supporting PCI host bridge hotplug.
I'm not convinced this is safe. But I'm not an RCU expert, so maybe
you can convince me :)
Documentation/RCU/checklist.txt says the update code still requires
mutual exclusion, and I don't see any in list_add_sorted() or its
callers.
MMCONFIG accesses are already protected by the pci_config_lock
spinlock, so I don't think the performance advantages of RCU really
gain us anything in this situation.
It would definitely be simpler to just hold pci_config_lock while
updating and searching the pci_mmcfg_list, but if there are issues
with that, you can educate me about what they are and why this RCU
code is correct.
Bjorn
> Signed-off-by: Jiang Liu <jiang.liu@xxxxxxxxxx>
> ---
> arch/x86/pci/mmconfig-shared.c | 11 ++++++-----
> arch/x86/pci/mmconfig_32.c | 13 +++++++++++--
> arch/x86/pci/mmconfig_64.c | 13 +++++++++++--
> 3 files changed, 28 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/pci/mmconfig-shared.c b/arch/x86/pci/mmconfig-shared.c
> index 5e2cd2a..3bcc361 100644
> --- a/arch/x86/pci/mmconfig-shared.c
> +++ b/arch/x86/pci/mmconfig-shared.c
> @@ -17,6 +17,7 @@
> #include <linux/bitmap.h>
> #include <linux/dmi.h>
> #include <linux/slab.h>
> +#include <linux/rculist.h>
> #include <asm/e820.h>
> #include <asm/pci_x86.h>
> #include <asm/acpi.h>
> @@ -45,20 +46,20 @@ static __init void free_all_mmcfg(void)
> pci_mmconfig_remove(cfg);
> }
>
> -static __init void list_add_sorted(struct pci_mmcfg_region *new)
> +static __devinit void list_add_sorted(struct pci_mmcfg_region *new)
> {
> struct pci_mmcfg_region *cfg;
>
> /* keep list sorted by segment and starting bus number */
> - list_for_each_entry(cfg, &pci_mmcfg_list, list) {
> + list_for_each_entry_rcu(cfg, &pci_mmcfg_list, list) {
> if (cfg->segment > new->segment ||
> (cfg->segment == new->segment &&
> cfg->start_bus >= new->start_bus)) {
> - list_add_tail(&new->list, &cfg->list);
> + list_add_tail_rcu(&new->list, &cfg->list);
> return;
> }
> }
> - list_add_tail(&new->list, &pci_mmcfg_list);
> + list_add_tail_rcu(&new->list, &pci_mmcfg_list);
> }
>
> static __devinit struct pci_mmcfg_region *pci_mmconfig_alloc(int segment,
> @@ -111,7 +112,7 @@ struct pci_mmcfg_region *pci_mmconfig_lookup(int segment, int bus)
> {
> struct pci_mmcfg_region *cfg;
>
> - list_for_each_entry(cfg, &pci_mmcfg_list, list)
> + list_for_each_entry_rcu(cfg, &pci_mmcfg_list, list)
> if (cfg->segment == segment &&
> cfg->start_bus <= bus && bus <= cfg->end_bus)
> return cfg;
> diff --git a/arch/x86/pci/mmconfig_32.c b/arch/x86/pci/mmconfig_32.c
> index 5372e86..5dad04a 100644
> --- a/arch/x86/pci/mmconfig_32.c
> +++ b/arch/x86/pci/mmconfig_32.c
> @@ -11,6 +11,7 @@
>
> #include <linux/pci.h>
> #include <linux/init.h>
> +#include <linux/rcupdate.h>
> #include <asm/e820.h>
> #include <asm/pci_x86.h>
> #include <acpi/acpi.h>
> @@ -60,9 +61,12 @@ err: *value = -1;
> return -EINVAL;
> }
>
> + rcu_read_lock();
> base = get_base_addr(seg, bus, devfn);
> - if (!base)
> + if (!base) {
> + rcu_read_unlock();
> goto err;
> + }
>
> raw_spin_lock_irqsave(&pci_config_lock, flags);
>
> @@ -80,6 +84,7 @@ err: *value = -1;
> break;
> }
> raw_spin_unlock_irqrestore(&pci_config_lock, flags);
> + rcu_read_unlock();
>
> return 0;
> }
> @@ -93,9 +98,12 @@ static int pci_mmcfg_write(unsigned int seg, unsigned int bus,
> if ((bus > 255) || (devfn > 255) || (reg > 4095))
> return -EINVAL;
>
> + rcu_read_lock();
> base = get_base_addr(seg, bus, devfn);
> - if (!base)
> + if (!base) {
> + rcu_read_unlock();
> return -EINVAL;
> + }
>
> raw_spin_lock_irqsave(&pci_config_lock, flags);
>
> @@ -113,6 +121,7 @@ static int pci_mmcfg_write(unsigned int seg, unsigned int bus,
> break;
> }
> raw_spin_unlock_irqrestore(&pci_config_lock, flags);
> + rcu_read_unlock();
>
> return 0;
> }
> diff --git a/arch/x86/pci/mmconfig_64.c b/arch/x86/pci/mmconfig_64.c
> index 915a493..acc48c5 100644
> --- a/arch/x86/pci/mmconfig_64.c
> +++ b/arch/x86/pci/mmconfig_64.c
> @@ -9,6 +9,7 @@
> #include <linux/init.h>
> #include <linux/acpi.h>
> #include <linux/bitmap.h>
> +#include <linux/rcupdate.h>
> #include <asm/e820.h>
> #include <asm/pci_x86.h>
>
> @@ -34,9 +35,12 @@ err: *value = -1;
> return -EINVAL;
> }
>
> + rcu_read_lock();
> addr = pci_dev_base(seg, bus, devfn);
> - if (!addr)
> + if (!addr) {
> + rcu_read_unlock();
> goto err;
> + }
>
> switch (len) {
> case 1:
> @@ -49,6 +53,7 @@ err: *value = -1;
> *value = mmio_config_readl(addr + reg);
> break;
> }
> + rcu_read_unlock();
>
> return 0;
> }
> @@ -62,9 +67,12 @@ static int pci_mmcfg_write(unsigned int seg, unsigned int bus,
> if (unlikely((bus > 255) || (devfn > 255) || (reg > 4095)))
> return -EINVAL;
>
> + rcu_read_lock();
> addr = pci_dev_base(seg, bus, devfn);
> - if (!addr)
> + if (!addr) {
> + rcu_read_unlock();
> return -EINVAL;
> + }
>
> switch (len) {
> case 1:
> @@ -77,6 +85,7 @@ static int pci_mmcfg_write(unsigned int seg, unsigned int bus,
> mmio_config_writel(addr + reg, value);
> break;
> }
> + rcu_read_unlock();
>
> return 0;
> }
> --
> 1.7.5.4
>
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