Messages in this thread | | | Date | Fri, 16 Dec 2011 12:56:29 -0800 | From | Frank Rowand <> | Subject | Re: [PATCH] PREEMPT_RT_FULL: ARM context switch needs IRQs enabled |
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On 12/15/11 19:20, Frank Rowand wrote: > > ARMv6 and later have VIPT caches and the TLBs are tagged with an ASID > (application specific ID). The number of ASIDs is limited to 256 and > the allocation algorithm requires IPIs when all the ASIDs have been > used. The IPIs require interrupts enabled during context switch for > deadlock avoidance. > > The RT patch mm-protect-activate-switch-mm.patch disables irqs around > activate_mm() and switch_mm(), which are the portion of the ARMv6 > context switch that require interrupts enabled. > > The solution for the ARMv6 processors could be to _not_ disable irqs. > A more conservative solution is to provide the same environment that > the scheduler provides, that is preempt_disable(). This is more > resilient for possible future changes to the ARM context switch code > that is not aware of the RT patches. > > This patch will conflict slightly with Catalin's patch set to remove > __ARCH_WANT_INTERRUPTS_ON_CTXSW, when that is accepted: > > http://lkml.indiana.edu/hypermail/linux/kernel/1111.3/01893.html > > When Catalin's patch set is accepted, this RT patch will need to reverse > the change in patch 6 to arch/arm/include/asm/system.h: > > -#ifndef CONFIG_CPU_HAS_ASID > -#define __ARCH_WANT_INTERRUPTS_ON_CTXSW > -#endif > > Signed-off-by: Frank Rowand <frank.rowand@am.sony.com> > > --- > fs/exec.c | 8 8 + 0 - 0 ! > mm/mmu_context.c | 8 8 + 0 - 0 ! > 2 files changed, 16 insertions(+) > > Index: b/fs/exec.c > =================================================================== > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -837,12 +837,20 @@ static int exec_mmap(struct mm_struct *m > } > } > task_lock(tsk); > +#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
Self critique... I really, really dislike this ifdef because it will fail silently if the includes are changed and as a result the include file that defines __ARCH_WANT_INTERRUPTS_ON_CTXSW (arch/arm/include/asm/system.h) is not included.
Does anyone have any brilliant ideas for an alternative approach?
-Frank
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