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Date: Tue, 5 Jul 2016 11:42:02 -0400 (EDT)
From: Alan Stern <stern@rowland.harvard.edu>
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To: Dmitry Vyukov <dvyukov@google.com>
cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Vegard Nossum <vegard.nossum@oracle.com>, <chunfeng.yun@mediatek.com>,
        <geert@linux-m68k.org>, USB list <linux-usb@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        syzkaller <syzkaller@googlegroups.com>,
        Kostya Serebryany <kcc@google.com>,
        Alexander Potapenko <glider@google.com>
Subject: Re: usb: memory allocation WARNING in hcd_buffer_alloc
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On Tue, 5 Jul 2016, Dmitry Vyukov wrote:

> Hello,
> 
> The following program trigger the following WARNING:
> 
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 6263 at mm/page_alloc.c:3584[<     inline     >]
> __alloc_pages_slowpath mm/page_alloc.c:3584
> WARNING: CPU: 0 PID: 6263 at mm/page_alloc.c:3584[<      none      >]
> __alloc_pages_nodemask+0x1731/0x2350 mm/page_alloc.c:3854
> Modules linked in:
> CPU: 0 PID: 6263 Comm: a.out Not tainted 4.7.0-rc5+ #28
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>  ffffffff880b58e0 ffff88006ad3f778 ffffffff82cc01af ffffffff86cf92c0
>  fffffbfff1016b1c 0000000000000000 0000000000000000 ffffffff86cf92c0
>  ffffffff816b7881 0000000000000009 ffff88006ad3f7c0 ffffffff8136d17f
> Call Trace:
>  [<     inline     >] __dump_stack lib/dump_stack.c:15
>  [<ffffffff82cc01af>] dump_stack+0x12e/0x18f lib/dump_stack.c:51
>  [<ffffffff8136d17f>] __warn+0x19f/0x1e0 kernel/panic.c:516
>  [<ffffffff8136d38c>] warn_slowpath_null+0x2c/0x40 kernel/panic.c:551
>  [<     inline     >] __alloc_pages_slowpath mm/page_alloc.c:3584
>  [<ffffffff816b7881>] __alloc_pages_nodemask+0x1731/0x2350 mm/page_alloc.c:3854
>  [<     inline     >] __alloc_pages include/linux/gfp.h:432
>  [<     inline     >] __alloc_pages_node include/linux/gfp.h:445
>  [<     inline     >] alloc_pages_node include/linux/gfp.h:459
>  [<ffffffff8120b28f>] dma_generic_alloc_coherent+0xff/0x250
> arch/x86/kernel/pci-dma.c:102
>  [<     inline     >] dma_alloc_attrs include/linux/dma-mapping.h:374
>  [<     inline     >] dma_alloc_coherent include/linux/dma-mapping.h:401
>  [<ffffffff84699f1d>] hcd_buffer_alloc+0x1dd/0x400 drivers/usb/core/buffer.c:140
>  [<ffffffff8465a670>] usb_alloc_coherent+0x60/0x80 drivers/usb/core/usb.c:740
>  [<ffffffff846a12ba>] usbdev_mmap+0x19a/0x650 drivers/usb/core/devio.c:244
>  [<ffffffff8175ae2f>] mmap_region+0x87f/0xfe0 mm/mmap.c:1507
>  [<ffffffff8175bf2d>] do_mmap+0x99d/0xbf0 mm/mmap.c:1286
>  [<     inline     >] do_mmap_pgoff include/linux/mm.h:2005
>  [<ffffffff81701e66>] vm_mmap_pgoff+0x156/0x1a0 mm/util.c:302
>  [<     inline     >] SYSC_mmap_pgoff mm/mmap.c:1336
>  [<ffffffff81754dea>] SyS_mmap_pgoff+0x34a/0x580 mm/mmap.c:1294
>  [<     inline     >] SYSC_mmap arch/x86/kernel/sys_x86_64.c:95
>  [<ffffffff81208ff6>] SyS_mmap+0x16/0x20 arch/x86/kernel/sys_x86_64.c:86
>  [<ffffffff86a94e00>] entry_SYSCALL_64_fastpath+0x23/0xc1
> arch/x86/entry/entry_64.S:207
> ---[ end trace 94402e12bc6578e5 ]---
> 
> // autogenerated by syzkaller (http://github.com/google/syzkaller)
> #include <pthread.h>
> #include <stdint.h>
> #include <string.h>
> #include <sys/syscall.h>
> #include <unistd.h>
> #include <sys/mman.h>
> 
> int main()
> {
>   int fd = open("/dev/bus/usb/001/001", 0x800ul, 0);
>   mmap((void*)0x201c4000ul, 0xc00000ul, 0x3ul, 0x20012ul, fd, 0x0ul);
>   return 0;
> }
> 
> On commit 1a0a02d1efa066001fd315c1b4df583d939fa2c4 (Jun 30).

This is an attempt to allocate 12 MB of coherent memory.  As far as I 
can tell, the WARNING refers to invalid bits set in the gfp_mask.

However the original allocation comes from usbdev_mmap() in 
drivers/usb/core/devio.c:

	mem = usb_alloc_coherent(ps->dev, size, GFP_USER, &dma_handle);

I don't see how that ends up causing the WARNING.

Alan Stern