Commit 6a3cd5be authored by Ingo Rohloff's avatar Ingo Rohloff Committed by Greg Kroah-Hartman
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USB: usbfs: Use a spinlock instead of atomic accesses to tally used memory. 



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.

Acked-by: default avatarAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: default avatarIngo Rohloff <ingo.rohloff@lauterbach.com>
Link: https://lore.kernel.org/r/20220209123303.103340-2-ingo.rohloff@lauterbach.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent c3c9cee5

drivers/usb/core/devio.c

+22 −10
Original line number Diff line number Diff line
@@ -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)