[PATCH] ia64: fix floating-point preemption problem
There've been reports of problems with CONFIG_PREEMPT=y and the high floating point partition. This is caused by the possibility of preemption and rescheduling on a different processor while saving or restioirng the high partition. The only places where the FPU state is touched are in ptrace, in switch_to(), and where handling a floating-point exception. In switch_to() preemption is off. So it's only in trap.c and ptrace.c that we need to prevent preemption. Here is a patch that adds commentary to make the conditions clear, and adds appropriate preempt_{en,dis}able() calls to make it so. In trap.c I use preempt_enable_no_resched(), as we're about to return to user space where the preemption flag will be checked anyway. Signed-off-by: Peter Chubb <peterc@gelato.unsw.edu.au> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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@ -635,11 +635,17 @@ ia64_flush_fph (struct task_struct *task)
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{
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struct ia64_psr *psr = ia64_psr(ia64_task_regs(task));
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/*
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* Prevent migrating this task while
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* we're fiddling with the FPU state
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*/
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preempt_disable();
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if (ia64_is_local_fpu_owner(task) && psr->mfh) {
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psr->mfh = 0;
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task->thread.flags |= IA64_THREAD_FPH_VALID;
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ia64_save_fpu(&task->thread.fph[0]);
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}
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preempt_enable();
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}
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/*
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@ -220,13 +220,21 @@ disabled_fph_fault (struct pt_regs *regs)
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/* first, grant user-level access to fph partition: */
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psr->dfh = 0;
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/*
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* Make sure that no other task gets in on this processor
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* while we're claiming the FPU
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*/
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preempt_disable();
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#ifndef CONFIG_SMP
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{
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struct task_struct *fpu_owner
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= (struct task_struct *)ia64_get_kr(IA64_KR_FPU_OWNER);
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if (ia64_is_local_fpu_owner(current))
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if (ia64_is_local_fpu_owner(current)) {
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preempt_enable_no_resched();
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return;
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}
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if (fpu_owner)
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ia64_flush_fph(fpu_owner);
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@ -244,6 +252,7 @@ disabled_fph_fault (struct pt_regs *regs)
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*/
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psr->mfh = 1;
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}
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preempt_enable_no_resched();
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}
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static inline int
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@ -403,7 +403,10 @@ extern void ia64_setreg_unknown_kr (void);
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* task_struct at this point.
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*/
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/* Return TRUE if task T owns the fph partition of the CPU we're running on. */
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/*
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* Return TRUE if task T owns the fph partition of the CPU we're running on.
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* Must be called from code that has preemption disabled.
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*/
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#define ia64_is_local_fpu_owner(t) \
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({ \
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struct task_struct *__ia64_islfo_task = (t); \
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@ -411,7 +414,10 @@ extern void ia64_setreg_unknown_kr (void);
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&& __ia64_islfo_task == (struct task_struct *) ia64_get_kr(IA64_KR_FPU_OWNER)); \
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})
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/* Mark task T as owning the fph partition of the CPU we're running on. */
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/*
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* Mark task T as owning the fph partition of the CPU we're running on.
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* Must be called from code that has preemption disabled.
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*/
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#define ia64_set_local_fpu_owner(t) do { \
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struct task_struct *__ia64_slfo_task = (t); \
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__ia64_slfo_task->thread.last_fph_cpu = smp_processor_id(); \
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