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

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Message-ID: <5363876A.2030709@imgtec.com>
Date:	Fri, 2 May 2014 12:54:18 +0100
From:	James Hogan <james.hogan@...tec.com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Helge Deller <deller@....de>
CC:	<linux-kernel@...r.kernel.org>, <linux-parisc@...r.kernel.org>,
	"John David Anglin" <dave.anglin@...l.net>,
	<linux-metag@...r.kernel.org>
Subject: Re: [PATCH] parisc,metag: Do not hardcode maximum userspace stack
 size

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

Thanks
James


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