Re: [RFC][PATCH] CMA: drivers/base/Kconfig: restrict CMA size to non-zero value
From: Gioh Kim
Date: Tue May 20 2014 - 20:15:25 EST
2014-05-20 ìí 8:38, Marek Szyprowski ì ê:
Hello,
On 2014-05-20 02:50, Gioh Kim wrote:
2014-05-20 ìì 4:59, Michal Nazarewicz ì ê:
On Sun, May 18 2014, Joonsoo Kim wrote:
I think that this problem is originated from atomic_pool_init().
If configured coherent_pool size is larger than default cma size,
it can be failed even if this patch is applied.
The coherent_pool size (atomic_pool.size) should be restricted smaller than cma size.
This is another issue, however I think the default atomic pool size is too small.
Only one port of USB host needs at most 256Kbytes coherent memory (according to the USB host spec).
This pool is used only for allocation done in atomic context (allocations
done with GFP_ATOMIC flag), otherwise the standard allocation path is used.
Are you sure that each usb host port really needs so much memory allocated
in atomic context?
I don't know why but drivers/usb/host/ohci-hcd.c:ohci_init() calls dma_alloc_coherent with zero gfp.
Therefore it occurs panic if CMA is turned on and CONFIG_CMA_SIZE_MBYTES is zero.
A pointer pool->vaddr is NULL in __alloc_from_pool.
Below is my kernel message.
[ 24.339858] -----------[ cut here ]-----------
[ 24.344535] WARNING: at arch/arm/mm/dma-mapping.c:492 __dma_alloc.isra.19+0x25c/0x2a4()
[ 24.352554] coherent pool not initialised!
[ 24.356644] Modules linked in:
[ 24.359701] CPU: 1 PID: 711 Comm: sh Not tainted 3.10.19+ #42
[ 24.365488] [<800140e0>] (unwind_backtrace+0x0/0xf8) from [<80011f20>] (show_stack+0x10/0x14)
[ 24.374045] [<80011f20>] (show_stack+0x10/0x14) from [<8001f21c>] (warn_slowpath_common+0x4c/0x6c)
[ 24.383022] [<8001f21c>] (warn_slowpath_common+0x4c/0x6c) from [<8001f2d0>] (warn_slowpath_fmt+0x30/0x40)
[ 24.392602] [<8001f2d0>] (warn_slowpath_fmt+0x30/0x40) from [<80017f5c>] (__dma_alloc.isra.19+0x25c/0x2a4)
[ 24.402270] [<80017f5c>] (__dma_alloc.isra.19+0x25c/0x2a4) from [<800180d0>] (arm_dma_alloc+0x90/0x98)
[ 24.411580] [<800180d0>] (arm_dma_alloc+0x90/0x98) from [<8034ab54>] (ohci_init+0x1b0/0x278)
[ 24.420035] [<8034ab54>] (ohci_init+0x1b0/0x278) from [<80332e00>] (usb_add_hcd+0x184/0x5b8)
[ 24.428484] [<80332e00>] (usb_add_hcd+0x184/0x5b8) from [<8034b8d4>] (ohci_platform_probe+0xd0/0x174)
[ 24.437713] [<8034b8d4>] (ohci_platform_probe+0xd0/0x174) from [<802f1cac>] (platform_drv_probe+0x14/0x18)
[ 24.447385] [<802f1cac>] (platform_drv_probe+0x14/0x18) from [<802f0a54>] (driver_probe_device+0x6c/0x1f8)
[ 24.457049] [<802f0a54>] (driver_probe_device+0x6c/0x1f8) from [<802ef16c>] (bus_for_each_drv+0x44/0x8c)
[ 24.466537] [<802ef16c>] (bus_for_each_drv+0x44/0x8c) from [<802f09bc>] (device_attach+0x74/0x80)
[ 24.475416] [<802f09bc>] (device_attach+0x74/0x80) from [<802f0050>] (bus_probe_device+0x84/0xa8)
[ 24.484295] [<802f0050>] (bus_probe_device+0x84/0xa8) from [<802ee89c>] (device_add+0x4c0/0x58c)
[ 24.493088] [<802ee89c>] (device_add+0x4c0/0x58c) from [<802f21b8>] (platform_device_add+0xac/0x214)
[ 24.502227] [<802f21b8>] (platform_device_add+0xac/0x214) from [<8001bf3c>] (lg115x_init_usb+0xbc/0xe4)
[ 24.511618] [<8001bf3c>] (lg115x_init_usb+0xbc/0xe4) from [<80008734>] (do_user_initcalls+0x98/0x128)
[ 24.520843] [<80008734>] (do_user_initcalls+0x98/0x128) from [<80008870>] (proc_write_usercalls+0xac/0xd0)
[ 24.530512] [<80008870>] (proc_write_usercalls+0xac/0xd0) from [<80138f48>] (proc_reg_write+0x58/0x80)
[ 24.539830] [<80138f48>] (proc_reg_write+0x58/0x80) from [<800f0084>] (vfs_write+0xb0/0x1bc)
[ 24.548275] [<800f0084>] (vfs_write+0xb0/0x1bc) from [<800f04d0>] (SyS_write+0x3c/0x70)
[ 24.556287] [<800f04d0>] (SyS_write+0x3c/0x70) from [<8000e5c0>] (ret_fast_syscall+0x0/0x30)
[ 24.564726] --[ end trace c092568e2a263d21 ]--
[ 24.569345] ohci-platform ohci-platform.0: can't setup
[ 24.574498] ohci-platform ohci-platform.0: USB bus 1 deregistered
[ 24.582241] ohci-platform: probe of ohci-platform.0 failed with error -12
[ 24.590496] ohci-platform ohci-platform.1: Generic Platform OHCI Controller
[ 24.598984] ohci-platform ohci-platform.1: new USB bus registered, assigned bus number 1
If a platform has several ports, it needs more than 1MB.
Therefore the default atomic pool size should be at least 1MB.
How about below patch?
It uses fallback allocation if CMA is failed.
Yes, I thought about it, but __dma_alloc uses similar code:
else if (!IS_ENABLED(CONFIG_DMA_CMA))
addr = __alloc_remap_buffer(dev, size, gfp, prot, &page, caller);
else
addr = __alloc_from_contiguous(dev, size, prot, &page, caller);
so it probably needs to be changed as well.
If CMA option is not selected, __alloc_from_contiguous would not be called.
We don't need to the fallback allocation.
And if CMA option is selected and initialized correctly,
the cma allocation can fail in case of no-CMA-memory situation.
I thinks in that case we don't need to the fallback allocation also,
because it is normal case.
Therefore I think the restriction of CMA size option and make CMA work can cover every cases.
I think below patch is also good choice.
If both of you, Michal and Joonsoo, do not agree with me, please inform me.
I will make a patch including option restriction and fallback allocation.
I'm not sure if we need a fallback for failed CMA allocation. The only issue that
have been mentioned here and needs to be resolved is support for disabling cma by
kernel command line. Right now it will fails completely.
cma=0 in the kernel command line and CONFIG_CMA_SIZE_MBYTES 0 are set selected_size as zero in dma_contiguous_reserve.
And dma_contiguous_reserve_area cannot be called and atomic_pool is not initialized.
After that dma_alloc_coherent try to allocate via atomic_pool (__alloc_from_pool) or CMA (__alloc_from_contiguous).
Allocation via atomic_pool fails becauseof atomic_pool->vaddr is NULL.
And CMA allocation shouldn't be called because cma=0 or setting CONFIG_CMA_SIZE_MBYTES 0 is the same with disabling CMA.
If cma=0 or CONFIG_CMA_SIZE_MBYTES is 0, __alloc_remap_buffer should be called instead of __alloc_from_contiguous even-if CMA is turned on.
I'm poor at English so I describe the problem in seudo code:
if (CMA is turned on) and ((cma=0 in command line) or (CONFIG_CMA_SIZE_MBYTES=0))
try to allocate from CMA but CMA is not initialized
Best regards
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