Re: [PATCH 2/8] MIPS: pci-rt2880: remove unneeded locks

[Sergey Ryazanov <ryazanov.s.a@gmail.com>]

On Tue, Apr 13, 2021 at 4:28 PM Sergey Ryazanov <ryazanov.s.a@gmail.com> wrote:
> On Tue, Apr 13, 2021 at 9:22 AM Ilya Lipnitskiy
> <ilya.lipnitskiy@gmail.com> wrote:
> > Mirror pci-rt3883 fix from commit e5067c718b3a ("MIPS: pci-rt3883:
> > Remove odd locking in PCI config space access code"). pci-rt2880 shares
> > the driver layout with pci-rt3883 and the same reasons apply.
> >
> > Caller (generic PCI code) already does proper locking, so no need to add
> > another one here. Local PCI read/write functions are never called
> > simultaneously, also they do not require synchronization with the PCI
> > controller ops, since they are used before the controller registration.
> >
> > Suggested-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
> > Signed-off-by: Ilya Lipnitskiy <ilya.lipnitskiy@gmail.com>
> > ---
> >  arch/mips/pci/pci-rt2880.c | 13 -------------
> >  1 file changed, 13 deletions(-)
> >
> > diff --git a/arch/mips/pci/pci-rt2880.c b/arch/mips/pci/pci-rt2880.c
> > index 19f7860fb28b..b4ee07cbcf2a 100644
> > --- a/arch/mips/pci/pci-rt2880.c
> > +++ b/arch/mips/pci/pci-rt2880.c
> > @@ -41,7 +41,6 @@
> >  #define RT2880_PCI_REG_ARBCTL          0x80
> >
> >  static void __iomem *rt2880_pci_base;
> > -static DEFINE_SPINLOCK(rt2880_pci_lock);
> >
> >  static u32 rt2880_pci_reg_read(u32 reg)
> >  {
> > @@ -63,7 +62,6 @@ static inline u32 rt2880_pci_get_cfgaddr(unsigned int bus, unsigned int slot,
> >  static int rt2880_pci_config_read(struct pci_bus *bus, unsigned int devfn,
> >                                   int where, int size, u32 *val)
> >  {
> > -       unsigned long flags;
> >         u32 address;
> >         u32 data;
> >         int busn = 0;
> > @@ -74,10 +72,8 @@ static int rt2880_pci_config_read(struct pci_bus *bus, unsigned int devfn,
> >         address = rt2880_pci_get_cfgaddr(busn, PCI_SLOT(devfn), PCI_FUNC(devfn),
> >                                          where);
> >
> > -       spin_lock_irqsave(&rt2880_pci_lock, flags);
> >         rt2880_pci_reg_write(address, RT2880_PCI_REG_CONFIG_ADDR);
> >         data = rt2880_pci_reg_read(RT2880_PCI_REG_CONFIG_DATA);
> > -       spin_unlock_irqrestore(&rt2880_pci_lock, flags);
> >
> >         switch (size) {
> >         case 1:
> > @@ -97,7 +93,6 @@ static int rt2880_pci_config_read(struct pci_bus *bus, unsigned int devfn,
> >  static int rt2880_pci_config_write(struct pci_bus *bus, unsigned int devfn,
> >                                    int where, int size, u32 val)
> >  {
> > -       unsigned long flags;
> >         u32 address;
> >         u32 data;
> >         int busn = 0;
> > @@ -108,7 +103,6 @@ static int rt2880_pci_config_write(struct pci_bus *bus, unsigned int devfn,
> >         address = rt2880_pci_get_cfgaddr(busn, PCI_SLOT(devfn), PCI_FUNC(devfn),
> >                                          where);
> >
> > -       spin_lock_irqsave(&rt2880_pci_lock, flags);
> >         rt2880_pci_reg_write(address, RT2880_PCI_REG_CONFIG_ADDR);
> >         data = rt2880_pci_reg_read(RT2880_PCI_REG_CONFIG_DATA);
> >
> > @@ -127,7 +121,6 @@ static int rt2880_pci_config_write(struct pci_bus *bus, unsigned int devfn,
> >         }
> >
> >         rt2880_pci_reg_write(data, RT2880_PCI_REG_CONFIG_DATA);
> > -       spin_unlock_irqrestore(&rt2880_pci_lock, flags);
> >
> >         return PCIBIOS_SUCCESSFUL;
> >  }
> > @@ -159,31 +152,25 @@ static struct pci_controller rt2880_pci_controller = {
> >
> >  static inline u32 rt2880_pci_read_u32(unsigned long reg)
> >  {
> > -       unsigned long flags;
> >         u32 address;
> >         u32 ret;
> >
> >         address = rt2880_pci_get_cfgaddr(0, 0, 0, reg);
> >
> > -       spin_lock_irqsave(&rt2880_pci_lock, flags);
> >         rt2880_pci_reg_write(address, RT2880_PCI_REG_CONFIG_ADDR);
> >         ret = rt2880_pci_reg_read(RT2880_PCI_REG_CONFIG_DATA);
> > -       spin_unlock_irqrestore(&rt2880_pci_lock, flags);
> >
> >         return ret;
> >  }
> >
> >  static inline void rt2880_pci_write_u32(unsigned long reg, u32 val)
> >  {
> > -       unsigned long flags;
> >         u32 address;
> >
> >         address = rt2880_pci_get_cfgaddr(0, 0, 0, reg);
> >
> > -       spin_lock_irqsave(&rt2880_pci_lock, flags);
> >         rt2880_pci_reg_write(address, RT2880_PCI_REG_CONFIG_ADDR);
> >         rt2880_pci_reg_write(val, RT2880_PCI_REG_CONFIG_DATA);
> > -       spin_unlock_irqrestore(&rt2880_pci_lock, flags);
> >  }
> >
> >  int pcibios_map_irq(const struct pci_dev *dev, u8 slot, u8 pin)
>
> RT2880 PCI driver calls rt2880_pci_write_u32()/rt2880_pci_read_u32()
> from pcibios_map_irq(), which is called outside the scope of the
> pci_lock spinlock that is defined in /drivers/pci/access.c. So it
> looks like this could lead to a race between
> rt2880_pci_write_u32()/rt2880_pci_read_u32() and
> rt2880_pci_config_read()/rt2880_pci_config_write() functions.
>
> The code that uses rt2880_pci_write_u32()/rt2880_pci_read_u32() in the
> pcibios_map_irq() duplicates a BAR initialization procedure, which is
> already performed by the rt288x_pci_probe().
>
> Maybe we should remove duplicated code in the pcibios_map_irq() to
> reduce duplication and to avoid possible race in configuration space
> access?
>
> If you fix this possible race, feel free to add in the next patch version my
> Reviewed-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>

Whoops, I just checked the whole series on the patchwork and realized
that you already removed this duplicated code in the first patch of
the series. In such a case this patch is Ok. Sorry for bothering.

Reviewed-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>

-- 
Sergey