Re: [PATCH] ppc32: fix destroy_context() race condition
From: Eugene Surovegin <hidden>
Date: 2005-07-12 16:39:23
On Tue, Jul 12, 2005 at 10:23:51AM -0400, Guillaume Autran wrote:
quoted hunk ↗ jump to hunk
Fix for a race condition when a task gets preempted by another task while executing the destroy_context(...) in a FEW_CONTEXTS environment. mm->context == NO_CONTEXT but the context_map may indicate all contexts are in use. The solution to this problem is to disable kernel preemption while destroying a MMU context. Signed-off-by: Guillaume Autran <redacted> --- diff -Nru a/include/asm-ppc/mmu_context.h b/include/asm-ppc/mmu_context.h--- a/include/asm-ppc/mmu_context.h 2005-06-17 15:48:29.000000000 -0400 +++ b/include/asm-ppc/mmu_context.h 2005-07-05 08:58:46.000000000 -0400@@ -149,6 +149,7 @@*/ static inline void destroy_context(struct mm_struct *mm) { + preempt_disable(); if (mm->context != NO_CONTEXT) { clear_bit(mm->context, context_map); mm->context = NO_CONTEXT;@@ -156,6 +157,7 @@atomic_inc(&nr_free_contexts); #endif } + preempt_enable(); } static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
Could you explain, why this patch is needed? AFAIK, destroy_context() is only called from switch_mm(), which in turn is called from schedule() with preemption already disabled. If not, IMHO we have bigger problems, and "fixing" destroy_context() will only hide such problems. -- Eugene