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Subject[PATCH 0/8] cpumask: Replace/optimize cpumask_of_cpu & cpumask_t operations

> From Rusty Russell <rusty@rustcorp.com.au>:
>
> Hi Christoph/Mike,
>
> Looked at cpumask_of_cpu as introduced in
> 9f0e8d0400d925c3acd5f4e01dbeb736e4011882 (x86: convert cpumask_of_cpu
> macro to allocated array), and I don't think it's safe:
>
> #define cpumask_of_cpu(cpu) \
> (*({ \
> typeof(_unused_cpumask_arg_) m; \
> if (sizeof(m) == sizeof(unsigned long)) { \
> m.bits[0] = 1UL<<(cpu); \
> } else { \
> cpus_clear(m); \
> cpu_set((cpu), m); \
> } \
> &m; \
> }))
>
> Referring to &m once out of scope is invalid, and I can't find any
> evidence that it's legal here. In particular, the change
> b53e921ba1cff8453dc9a87a84052fa12d5b30bd (generic: reduce stack pressure
> in sched_affinity) which passes &m to other functions seems highly risky.

* Patch 1 replaces the dangerous lvalue version of cpumask_of_cpu
with new cpumask_of_cpu_ptr macros. These are patterned after the
node_to_cpumask_ptr macros.

* Patches 2..6 optimizes various places where a pointer to the cpumask_of_cpu
value will result in reducing stack pressure.

* Patch 7 provides a generic set of CPUMASK_ALLOC macros patterned after
the SCHED_CPUMASK_ALLOC macros. This is used where multiple cpumask_t
variables are declared on the stack to reduce the amount of stack space
required.

* Patch 8 uses the CPUMASK_ALLOC macros in the centrino_target() function.

Based on linux-2.6.tip/master at the following commit:

commit 0a91813e16ebd5c2d9b5c2acd5b7c91742112c4f
Merge: 9a635fa... 724dce0...
Author: Ingo Molnar <mingo@elte.hu>
Date: Tue Jul 15 14:55:17 2008 +0200


Signed-off-by: Mike Travis <travis@sgi.com>
Cc: Tigran Aivazian <tigran@aivazian.fsnet.co.uk>
Cc: Greg Banks <gnb@sgi.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Adrian Bunk <bunk@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paul Jackson <pj@sgi.com>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Dean Nelson <dcn@sgi.com>
Cc: Venki Pallipadi <venkatesh.pallipadi@intel.com>
Cc: Robert Richter <robert.richter@amd.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
---
--


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