On 06/12/2018 15:11, Tony Battersby wrote:
On 12/6/18 4:25 AM, Krzysztof Kozlowski wrote:
On Thu, 6 Dec 2018 at 02:31, Tony Lindgren <tony@xxxxxxxxxxx> wrote:
Hi,
Looks like with commit 26abe88e830d ("mm/dmapool.c: improve scalability
of dma_pool_free()") I'm now getting spammed with lots of "(bad vaddr)"
on at least omap4 pandaboard, see below.
Any ideas what might be going wrong?
Regards,
Tony
8< ---------------------
omap-dma-engine 4a056000.dma-controller: dma_pool_free 4a056000.dma-controller, (ptrval) (bad vaddr)/0xbe800000
omap-dma-engine 4a056000.dma-controller: dma_pool_free 4a056000.dma-controller, (ptrval) (bad vaddr)/0xbe80001c
omap-dma-engine 4a056000.dma-controller: dma_pool_free 4a056000.dma-controller, (ptrval) (bad vaddr)/0xbe800038
...
I see it as well on all my Exynos boards, since yesterday's next. In
my case it is the USB EHCI driver:
exynos-ehci 12110000.usb: dma_pool_free ehci_qtd, (ptrval) (bad
vaddr)/0xb8844180
Full log here:
https://krzk.eu/#/builders/1/builds/2937/steps/12/logs/serial0
Best regards,
Krzysztof
Here is the prototype:
void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t dma);
With the old code, the 'dma' value had to be correct for use with
pool_find_page(), or else you would get an error. If the 'vaddr' value
was incorrect, it would corrupt the dmapool freelist, but you wouldn't
get an error unless DMAPOOL_DEBUG was enabled.
With my patch applied, 'vaddr' has to be correct for virt_to_page(). My
code also checks that 'dma' is consistent with 'vaddr' even if
DMAPOOL_DEBUG is disabled, since the check is fast and it will prevent
problems like this in the future.
Unfortunately that logic has a fatal flaw - DMA pools are backed by
dma_alloc_coherent(), and there is absolutely no guarantee that the
memory dma_alloc_coherent() returns is backed by a struct page at all.
Even if it is, there is still absolutely no guarantee that the vaddr
value it returns is valid for virt_to_page() - on many systems it will
be in vmalloc or some architecture-specific region of address space.
The problem is not that these drivers are buggy (they're not - the arch
code is returning a vmalloc()ed non-cacheable remap in the first place),
it's that 26abe88e830d is fundamentally unworkable and needs reverting.
Apparently the original patches managed not to catch my eye as something
I needed to review, sorry about that :(
Robin.
So if a buggy driver passes in a good value for 'dma' but a bad value
for 'vaddr', then it may have appeared to work previously (but with
possible data corruption, depending on the circumstances), but my patch
will expose the problem. You can confirm by reverting my dmapool
patches and enabling DMAPOOL_DEBUG, which is at the top of mm/dmapool.c:
#if defined(CONFIG_DEBUG_SLAB) || defined(CONFIG_SLUB_DEBUG_ON)
#define DMAPOOL_DEBUG 1
#endif
Tony Battersby
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