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 > -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html