From 6a3cd5bef2531a1178234efa3bed788e3b3831f0 Mon Sep 17 00:00:00 2001
From: Ingo Rohloff <ingo.rohloff@lauterbach.com>
Date: Wed, 9 Feb 2022 13:33:03 +0100
Subject: [PATCH] USB: usbfs: Use a spinlock instead of atomic accesses to
tally used memory.
Git-commit: 6a3cd5bef2531a1178234efa3bed788e3b3831f0
References: jsc#PED-531
Patch-mainline: v5.18-rc1
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: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Ingo Rohloff <ingo.rohloff@lauterbach.com>
Link: https://lore.kernel.org/r/20220209123303.103340-2-ingo.rohloff@lauterbach.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
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)
--
2.35.3