| Message ID | 20220209123303.103340-2-ingo.rohloff@lauterbach.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 6a3cd5bef2531a1178234efa3bed788e3b3831f0 |
| Headers | show |
| Series | USB: usbfs: replace atomic64 accesses by spinlock | expand |
On Wed, Feb 09, 2022 at 01:33:03PM +0100, Ingo Rohloff wrote: > While the existing code code imposes a limit on the used memory, it might be > over pessimistic (even if this is unlikely). > > Example scenario: > 8 threads running in parallel, all entering > "usbfs_increase_memory_usage()" at the same time. > The atomic accesses in "usbfs_increase_memory_usage()" could be > serialized like this: > 8 x "atomic64_add" > 8 x "atomic64_read" > If the 8 x "atomic64_add" raise "usbfs_memory_usage" above the limit, > then all 8 calls of "usbfs_increase_memory_usage()" will return with > -ENOMEM. If you instead serialize over the whole access to > "usbfs_memory_usage" by using a spinlock, some of these calls will > succeed. > > Signed-off-by: Ingo Rohloff <ingo.rohloff@lauterbach.com> > --- Acked-by: Alan Stern <stern@rowland.harvard.edu> > drivers/usb/core/devio.c | 32 ++++++++++++++++++++++---------- > 1 file changed, 22 insertions(+), 10 deletions(-) > > diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c > index fa66e6e58792..6abb7294e919 100644 > --- a/drivers/usb/core/devio.c > +++ b/drivers/usb/core/devio.c > @@ -139,30 +139,42 @@ MODULE_PARM_DESC(usbfs_memory_mb, > /* Hard limit, necessary to avoid arithmetic overflow */ > #define USBFS_XFER_MAX (UINT_MAX / 2 - 1000000) > > -static atomic64_t usbfs_memory_usage; /* Total memory currently allocated */ > +static DEFINE_SPINLOCK(usbfs_memory_usage_lock); > +static u64 usbfs_memory_usage; /* Total memory currently allocated */ > > /* Check whether it's okay to allocate more memory for a transfer */ > static int usbfs_increase_memory_usage(u64 amount) > { > - u64 lim; > + u64 lim, total_mem; > + unsigned long flags; > + int ret; > > lim = READ_ONCE(usbfs_memory_mb); > lim <<= 20; > > - atomic64_add(amount, &usbfs_memory_usage); > - > - if (lim > 0 && atomic64_read(&usbfs_memory_usage) > lim) { > - atomic64_sub(amount, &usbfs_memory_usage); > - return -ENOMEM; > - } > + ret = 0; > + spin_lock_irqsave(&usbfs_memory_usage_lock, flags); > + total_mem = usbfs_memory_usage + amount; > + if (lim > 0 && total_mem > lim) > + ret = -ENOMEM; > + else > + usbfs_memory_usage = total_mem; > + spin_unlock_irqrestore(&usbfs_memory_usage_lock, flags); > > - return 0; > + return ret; > } > > /* Memory for a transfer is being deallocated */ > static void usbfs_decrease_memory_usage(u64 amount) > { > - atomic64_sub(amount, &usbfs_memory_usage); > + unsigned long flags; > + > + spin_lock_irqsave(&usbfs_memory_usage_lock, flags); > + if (amount > usbfs_memory_usage) > + usbfs_memory_usage = 0; > + else > + usbfs_memory_usage -= amount; > + spin_unlock_irqrestore(&usbfs_memory_usage_lock, flags); > } > > static int connected(struct usb_dev_state *ps) > -- > 2.17.1 >
diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c index fa66e6e58792..6abb7294e919 100644 --- a/drivers/usb/core/devio.c +++ b/drivers/usb/core/devio.c @@ -139,30 +139,42 @@ MODULE_PARM_DESC(usbfs_memory_mb, /* Hard limit, necessary to avoid arithmetic overflow */ #define USBFS_XFER_MAX (UINT_MAX / 2 - 1000000) -static atomic64_t usbfs_memory_usage; /* Total memory currently allocated */ +static DEFINE_SPINLOCK(usbfs_memory_usage_lock); +static u64 usbfs_memory_usage; /* Total memory currently allocated */ /* Check whether it's okay to allocate more memory for a transfer */ static int usbfs_increase_memory_usage(u64 amount) { - u64 lim; + u64 lim, total_mem; + unsigned long flags; + int ret; lim = READ_ONCE(usbfs_memory_mb); lim <<= 20; - atomic64_add(amount, &usbfs_memory_usage); - - if (lim > 0 && atomic64_read(&usbfs_memory_usage) > lim) { - atomic64_sub(amount, &usbfs_memory_usage); - return -ENOMEM; - } + ret = 0; + spin_lock_irqsave(&usbfs_memory_usage_lock, flags); + total_mem = usbfs_memory_usage + amount; + if (lim > 0 && total_mem > lim) + ret = -ENOMEM; + else + usbfs_memory_usage = total_mem; + spin_unlock_irqrestore(&usbfs_memory_usage_lock, flags); - return 0; + return ret; } /* Memory for a transfer is being deallocated */ static void usbfs_decrease_memory_usage(u64 amount) { - atomic64_sub(amount, &usbfs_memory_usage); + unsigned long flags; + + spin_lock_irqsave(&usbfs_memory_usage_lock, flags); + if (amount > usbfs_memory_usage) + usbfs_memory_usage = 0; + else + usbfs_memory_usage -= amount; + spin_unlock_irqrestore(&usbfs_memory_usage_lock, flags); } static int connected(struct usb_dev_state *ps)
While the existing code code imposes a limit on the used memory, it might be over pessimistic (even if this is unlikely). Example scenario: 8 threads running in parallel, all entering "usbfs_increase_memory_usage()" at the same time. The atomic accesses in "usbfs_increase_memory_usage()" could be serialized like this: 8 x "atomic64_add" 8 x "atomic64_read" If the 8 x "atomic64_add" raise "usbfs_memory_usage" above the limit, then all 8 calls of "usbfs_increase_memory_usage()" will return with -ENOMEM. If you instead serialize over the whole access to "usbfs_memory_usage" by using a spinlock, some of these calls will succeed. Signed-off-by: Ingo Rohloff <ingo.rohloff@lauterbach.com> --- drivers/usb/core/devio.c | 32 ++++++++++++++++++++++---------- 1 file changed, 22 insertions(+), 10 deletions(-)