Re: [PATCH] parisc,metag: Do not hardcode maximum userspace stack size

Helge Deller
2014-05-13T19:45:14Z

Hi James,

On 05/13/2014 01:18 PM, James Hogan wrote:
> On 04/05/14 08:28, Helge Deller wrote:
>> On 05/02/2014 04:48 PM, James Bottomley wrote:
>>> On Fri, 2014-05-02 at 12:54 +0100, James Hogan wrote:
>>>> On 01/05/14 18:50, James Bottomley wrote:
>>>>>
>>>>>> +config MAX_STACK_SIZE_MB
>>>>>> + int "Maximum user stack size (MB)"
>>>>>> + default 80
>>>>>> + range 8 256 if METAG
>>>>>> + range 8 2048
>>>>>> + depends on STACK_GROWSUP
>>>>>> + help
>>>>>> + This is the maximum stack size in Megabytes in the VM layout of user
>>>>>> + processes when the stack grows upwards (currently only on parisc and
>>>>>> + metag arch). The stack will be located at the highest memory address
>>>>>> + minus the given value, unless the RLIMIT_STACK hard limit is changed
>>>>>> + to a smaller value in which case that is used.
>>>>>> +
>>>>>> + A sane initial value is 80 MB.
>>>>>
>>>>> There's one final issue with this: placement of the stack only really
>>>>> matters on 32 bits. We have three expanding memory areas: stack, heap
>>>>> and maps. On 64 bits these are placed well separated from each other on
>>>>> 64 bits, so an artificial limit like this doesn't matter.
>>>>
>>>> Does the following fixup diff look reasonable? It forces
>>>> MAX_STACK_SIZE_MB to 1024 and hides the Kconfig option for 64BIT,
>>>> effectively leaving the behaviour unchanged in that case.
>>>>
>>>> diff --git a/mm/Kconfig b/mm/Kconfig
>>>> index e80075979530..b0307f737bd7 100644
>>>> --- a/mm/Kconfig
>>>> +++ b/mm/Kconfig
>>>> @@ -583,7 +583,8 @@ config GENERIC_EARLY_IOREMAP
>>>> bool
>>>>
>>>> config MAX_STACK_SIZE_MB
>>>> - int "Maximum user stack size (MB)"
>>>> + int "Maximum user stack size (MB)" if !64BIT
>>>> + default 1024 if 64BIT
>>>> default 80
>>>> range 8 256 if METAG
>>>> range 8 2048
>>>
>>> Yes, I think that's probably correct ...
>>
>> No, it's not correct.
>> It will then choose then a 1GB stack for compat tasks on 64bit kernel.
>
> Sorry for the delay (I had most of last week off sick and still catching
> up).

No problem.

> That's a good point. It makes me think the best way to handle it is in a
> new definition in asm/processor.h, maybe STACK_SIZE_MAX. Does something
> like this look better? This patch isn't getting any cleaner
> unfortunately.

Yes, it's correct now.
Just tested it. Thanks!

Another problem:
I think you wanted to get it backported into older kernels?
It seems the changes to mm/Kconfig will not apply cleanly to 3.14 or lower,
and the changes to arch/parisc/kernel/sys_parisc.c will not apply to 3.13 or lower...

Maybe cleaning up the patch to apply cleanly to 3.14 would make sense
and ignore older kernels?

Helge

> From 6ecb0392a3b670c4bf1641a6ec56f22427ca8b57 Mon Sep 17 00:00:00 2001
> From: Helge Deller <deller@gmx.de>
> Date: Wed, 30 Apr 2014 23:26:02 +0200
> Subject: [PATCH 1/1] parisc,metag: Do not hardcode maximum userspace stack
> size
>
> This patch affects only architectures where the stack grows upwards
> (currently parisc and metag only). On those do not hardcode the maximum
> initial stack size to 1GB for 32-bit processes, but make it configurable
> via a config option.
>
> The main problem with the hardcoded stack size is, that we have two
> memory regions which grow upwards: stack and heap. To keep most of the
> memory available for heap in a flexmap memoy layout, it makes no sense
> to hard allocate up to 1GB of the memory for stack which can't be used
> as heap then.
>
> This patch makes the stack size configurable and uses 80MB as default
> value which has been in use during the last few years on parisc and
> which didn't showed any problems yet.
>
> This also fixes a BUG on metag if the RLIMIT_STACK hard limit is
> increased beyond a safe value by root. E.g. when starting a process
> after running "ulimit -H -s unlimited" it will then attempt to use a
> stack size of the maximum 1GB which is far too big for metag's limited
> user virtual address space (stack_top is usually 0x3ffff000):
> BUG: failure at fs/exec.c:589/shift_arg_pages()!
>
> Signed-off-by: Helge Deller <deller@gmx.de>
> Signed-off-by: James Hogan <james.hogan@imgtec.com>
> Cc: linux-parisc@vger.kernel.org
> Cc: linux-metag@vger.kernel.org
> Cc: John David Anglin <dave.anglin@bell.net>
> Cc: stable@vger.kernel.org # only needed for >= v3.9 (arch/metag)
> ---
> v3 (James Hogan):
> - fix so that 64-bit parisc processes still use the 1GB limit.
> CONFIG_STACK_GROWSUP arches should provide a STACK_SIZE_MAX in their
> asm/processor.h, and for parisc it depends on USER_WIDE_MODE (whether
> the current process is 64-bit).
> v2 (James Hogan):
> - updated description to mention BUG on metag.
> - added custom range limit for METAG.
> - moved Kconfig symbol to mm/Kconfig and reworded.
> - fixed "matag" typo.
> ---
> arch/metag/include/asm/processor.h | 2 ++
> arch/parisc/include/asm/processor.h | 5 +++++
> arch/parisc/kernel/sys_parisc.c | 6 +++---
> fs/exec.c | 6 +++---
> mm/Kconfig | 15 +++++++++++++++
> 5 files changed, 28 insertions(+), 6 deletions(-)
>
> diff --git a/arch/metag/include/asm/processor.h b/arch/metag/include/asm/processor.h
> index f16477d1f571..a8a37477c66e 100644
> --- a/arch/metag/include/asm/processor.h
> +++ b/arch/metag/include/asm/processor.h
> @@ -22,6 +22,8 @@
> /* Add an extra page of padding at the top of the stack for the guard page. */
> #define STACK_TOP (TASK_SIZE - PAGE_SIZE)
> #define STACK_TOP_MAX STACK_TOP
> +/* Maximum virtual space for stack */
> +#define STACK_SIZE_MAX (CONFIG_MAX_STACK_SIZE_MB*1024*1024)
>
> /* This decides where the kernel will search for a free chunk of vm
> * space during mmap's.
> diff --git a/arch/parisc/include/asm/processor.h b/arch/parisc/include/asm/processor.h
> index 198a86feb574..d951c9681ab3 100644
> --- a/arch/parisc/include/asm/processor.h
> +++ b/arch/parisc/include/asm/processor.h
> @@ -55,6 +55,11 @@
> #define STACK_TOP TASK_SIZE
> #define STACK_TOP_MAX DEFAULT_TASK_SIZE
>
> +/* Allow bigger stacks for 64-bit processes */
> +#define STACK_SIZE_MAX (USER_WIDE_MODE \
> + ? (1 << 30) /* 1 GB */ \
> + : (CONFIG_MAX_STACK_SIZE_MB*1024*1024))
> +
> #endif
>
> #ifndef __ASSEMBLY__
> diff --git a/arch/parisc/kernel/sys_parisc.c b/arch/parisc/kernel/sys_parisc.c
> index 31ffa9b55322..e1ffea2f9a0b 100644
> --- a/arch/parisc/kernel/sys_parisc.c
> +++ b/arch/parisc/kernel/sys_parisc.c
> @@ -72,10 +72,10 @@ static unsigned long mmap_upper_limit(void)
> {
> unsigned long stack_base;
>
> - /* Limit stack size to 1GB - see setup_arg_pages() in fs/exec.c */
> + /* Limit stack size - see setup_arg_pages() in fs/exec.c */
> stack_base = rlimit_max(RLIMIT_STACK);
> - if (stack_base > (1 << 30))
> - stack_base = 1 << 30;
> + if (stack_base > STACK_SIZE_MAX)
> + stack_base = STACK_SIZE_MAX;
>
> return PAGE_ALIGN(STACK_TOP - stack_base);
> }
> diff --git a/fs/exec.c b/fs/exec.c
> index 476f3ebf437e..238b7aa26f68 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -657,10 +657,10 @@ int setup_arg_pages(struct linux_binprm *bprm,
> unsigned long rlim_stack;
>
> #ifdef CONFIG_STACK_GROWSUP
> - /* Limit stack size to 1GB */
> + /* Limit stack size */
> stack_base = rlimit_max(RLIMIT_STACK);
> - if (stack_base > (1 << 30))
> - stack_base = 1 << 30;
> + if (stack_base > STACK_SIZE_MAX)
> + stack_base = STACK_SIZE_MAX;
>
> /* Make sure we didn't let the argument array grow too large. */
> if (vma->vm_end - vma->vm_start > stack_base)
> diff --git a/mm/Kconfig b/mm/Kconfig
> index ebe5880c29d6..1b5a95f0fa01 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -581,3 +581,18 @@ config PGTABLE_MAPPING
>
> config GENERIC_EARLY_IOREMAP
> bool
> +
> +config MAX_STACK_SIZE_MB
> + int "Maximum user stack size for 32-bit processes (MB)"
> + default 80
> + range 8 256 if METAG
> + range 8 2048
> + depends on STACK_GROWSUP && (!64BIT || COMPAT)
> + help
> + This is the maximum stack size in Megabytes in the VM layout of 32-bit
> + user processes when the stack grows upwards (currently only on parisc
> + and metag arch). The stack will be located at the highest memory
> + address minus the given value, unless the RLIMIT_STACK hard limit is
> + changed to a smaller value in which case that is used.
> +
> + A sane initial value is 80 MB.
>