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Subject: Re: [PATCH] dma-debug: fix soft lockup when a lot of debug are
 enabled
To:     Anders Roxell <anders.roxell@linaro.org>, hch@lst.de
Cc:     m.szyprowski@samsung.com, iommu@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, rostedt@goodmis.org
References: <20181211103616.22137-1-anders.roxell@linaro.org>
From:   Robin Murphy <robin.murphy@arm.com>
Message-ID: <613667c4-f850-d88c-7a2e-76dda5d966f5@arm.com>
Date:   Tue, 11 Dec 2018 11:51:14 +0000
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Hi Anders,

On 11/12/2018 10:36, Anders Roxell wrote:
> When running a kernel in qemu with enough debugging options (slub-debug,
> ftrace, kcov, kasan, ubsan, ...) enabled together, that results in a
> slow initcall. So a 'watchdog: BUG: soft lockup' happens:
> 
> [   44.105619] Call trace:
> [   44.106709]  __slab_alloc+0x70/0x88
> [   44.107757]  kmem_cache_alloc_trace+0x13c/0x590
> [   44.108764]  prealloc_memory+0xb8/0x240
> [   44.109768]  dma_debug_init+0x174/0x1f0
> [   44.110725]  do_one_initcall+0x430/0x8b0
> [   44.111719]  do_initcall_level+0x548/0x5b4
> [   44.112672]  do_initcalls+0x28/0x4c
> [   44.113628]  do_basic_setup+0x34/0x3c
> [   44.114559]  kernel_init_freeable+0x194/0x24c
> [   44.115570]  kernel_init+0x24/0x18c
> [   44.116498]  ret_from_fork+0x10/0x18
> 
> Rework to call cond_resched(), in the function prealloc_memory()'s
> for-loop.

Funnily enough I've just done a bit of work in this area which should 
make allocation a lot more efficient - would you mind giving this series 
a spin on the same setup to see how much it helps the performance?

https://lore.kernel.org/lkml/cover.1544447601.git.robin.murphy@arm.com/

Thanks,
Robin.

> 
> Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
> ---
>   kernel/dma/debug.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
> index 231ca4628062..2abdc265aec4 100644
> --- a/kernel/dma/debug.c
> +++ b/kernel/dma/debug.c
> @@ -767,6 +767,7 @@ static int prealloc_memory(u32 num_entries)
>   	int i;
>   
>   	for (i = 0; i < num_entries; ++i) {
> +		cond_resched();
>   		entry = kzalloc(sizeof(*entry), GFP_KERNEL);
>   		if (!entry)
>   			goto out_err;
>