From: arnd@arndb•de (Arnd Bergmann)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] USB: ehci: use packed, aligned(4) instead of removing the packed attribute
Date: Tue, 21 Jun 2011 13:25:16 +0200 [thread overview]
Message-ID: <201106211325.16777.arnd@arndb.de> (raw)
In-Reply-To: <alpine.LFD.2.00.1106201814490.2142@xanadu.home>
On Tuesday 21 June 2011, Nicolas Pitre wrote:
> On Mon, 20 Jun 2011, Arnd Bergmann wrote:
> This example is flawed. The DMA API documentation already forbids DMA to
> the stack because of cache line sharing issues. If you declare your
> buffer outside of the function body, the compiler can't optimize away
> the buffer store anymore, and this example works as expected without any
> memory clobber.
Ok, another example, even simpler:
int f(int *dma_buf, volatile int *mmio_reg)
{
(void) *mmio_reg; /* wait for DMA to complete */
return *dma_buf;
}
gcc-4.4, 4.5 and 4.6 all turn this into:
ldr r0, [r0, #0]
ldr r3, [r1, #0]
bx lr
which means that the dma_buf variable is dereferenced before the
volatile mmio_reg variable, which opens up a race: An interrupt may have
signalled us that a DMA is in progress, so we read a MMIO register from
the device (this is guaranteed to flush the DMA on PCI and similar buses).
If we read the dma_buf before we read the mmio register, the data we get
back may be stale.
Adding a barrier() between the two turns the assembly into the expected
ldr r3, [r1, #0]
ldr r0, [r0, #0]
bx lr
Arnd
next prev parent reply other threads:[~2011-06-21 11:25 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-27 14:34 [PATCH] echi: remove structure packing from ehci_def Rabin Vincent
2011-04-27 15:15 ` Sergei Shtylyov
2011-04-27 15:37 ` [PATCHv2] " Rabin Vincent
2011-06-16 16:17 ` [PATCH] USB: ehci: use packed, aligned(4) instead of removing the packed attribute Alexander Holler
2011-06-16 17:09 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern
2011-06-16 17:55 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann
2011-06-16 19:25 ` [PATCH] USB: ehci: use packed,aligned(4) " Alexander Holler
2011-06-16 19:46 ` Alan Stern
2011-06-16 20:10 ` Alexander Holler
2011-06-16 20:20 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann
2011-06-19 15:02 ` Nicolas Pitre
2011-06-19 19:00 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern
2011-06-19 20:02 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann
2011-06-19 20:11 ` Arnd Bergmann
2011-06-19 21:39 ` Nicolas Pitre
2011-06-19 21:27 ` Nicolas Pitre
2011-06-20 15:03 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern
2011-06-20 16:16 ` [PATCH] USB: ehci: use packed, aligned(4) " Nicolas Pitre
2011-06-20 16:48 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern
2011-06-20 16:58 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann
2011-06-20 19:02 ` Russell King - ARM Linux
2011-06-20 19:20 ` Nicolas Pitre
2011-06-20 19:29 ` Nicolas Pitre
2011-06-20 17:10 ` Nicolas Pitre
2011-06-20 17:35 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern
2011-06-20 18:48 ` Russell King - ARM Linux
2011-06-20 20:26 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann
2011-06-20 20:50 ` Nicolas Pitre
2011-06-20 20:55 ` [PATCH] USB: ehci: use packed,aligned(4) " Russell King - ARM Linux
2011-06-20 21:23 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann
2011-06-20 22:23 ` Nicolas Pitre
2011-06-21 11:25 ` Arnd Bergmann [this message]
2011-06-25 1:25 ` Nicolas Pitre
2011-06-25 8:09 ` Arnd Bergmann
2011-06-28 18:51 ` Nicolas Pitre
2011-06-29 10:56 ` Arnd Bergmann
2011-06-20 19:14 ` Nicolas Pitre
2011-06-20 19:32 ` Russell King - ARM Linux
2011-06-20 20:14 ` Arnd Bergmann
2011-06-20 20:42 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern
2011-06-20 22:36 ` [PATCH] USB: ehci: use packed, aligned(4) " Nicolas Pitre
2011-06-21 15:06 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern
2011-06-20 17:39 ` Alexander Holler
2011-06-20 18:39 ` Alan Stern
2011-06-20 18:46 ` Alexander Holler
2011-06-20 18:57 ` Alan Stern
2011-06-20 19:56 ` [PATCH] USB: ehci: use packed, aligned(4) " Nicolas Pitre
2011-06-20 21:04 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern
2011-06-20 22:31 ` [PATCH] USB: ehci: use packed, aligned(4) " Nicolas Pitre
2011-06-21 14:58 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern
2011-06-21 20:41 ` [PATCH] USB: ehci: use packed, aligned(4) " Nicolas Pitre
2011-06-22 6:23 ` [PATCH] USB: ehci: use packed,aligned(4) " Alexander Holler
2011-06-20 20:09 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann
2011-06-20 21:05 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern
2011-06-20 20:07 ` [PATCH] USB: ehci: use packed, aligned(4) " Arnd Bergmann
2011-06-20 20:28 ` Nicolas Pitre
2011-06-20 20:39 ` Arnd Bergmann
2011-06-20 21:03 ` Nicolas Pitre
2011-06-23 9:47 ` Alexander Holler
2011-06-23 14:25 ` Alan Stern
2011-06-24 11:40 ` Alexander Holler
2011-06-20 16:26 ` Arnd Bergmann
2011-06-16 20:30 ` [PATCH] USB: ehci: use packed,aligned(4) " Alan Stern
2011-06-16 18:16 ` Alexander Holler
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