From 2b4bc78956bdcc2bb4c49b3af955be776817e897 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (Red Hat)" Date: Sat, 22 Jun 2013 13:16:19 -0400 Subject: [PATCH] trace,x86: Do not call local_irq_save() in load_current_idt() As load_current_idt() is now what is used to update the IDT for the switches needed for NMI, lockdep debug, and for tracing, it must not call local_irq_save(). This is because one of the users of this is lockdep, which does tracing of local_irq_save() and when the debug trap is hit, we need to update the IDT before tracing interrupts being disabled. As load_current_idt() is used to do this, calling local_irq_save() which lockdep traces, defeats the point of calling load_current_idt(). As interrupts are already disabled when used by lockdep and NMI, the only other user is tracing that can disable interrupts itself. Simply have the tracing update disable interrupts before calling load_current_idt() instead of breaking the other users. Here's the dump that happened: ------------[ cut here ]------------ WARNING: at /work/autotest/nobackup/linux-test.git/kernel/fork.c:1196 copy_process+0x2c3/0x1398() DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled) Modules linked in: CPU: 1 PID: 4570 Comm: gdm-simple-gree Not tainted 3.10.0-rc3-test+ #5 Hardware name: /DG965MQ, BIOS MQ96510J.86A.0372.2006.0605.1717 06/05/2006 ffffffff81d2a7a5 ffff88006ed13d50 ffffffff8192822b ffff88006ed13d90 ffffffff81035f25 ffff8800721c6000 ffff88006ed13da0 0000000001200011 0000000000000000 ffff88006ed5e000 ffff8800721c6000 ffff88006ed13df0 Call Trace: [] dump_stack+0x19/0x1b [] warn_slowpath_common+0x67/0x80 [] warn_slowpath_fmt+0x46/0x48 [] ? __raw_spin_lock_init+0x31/0x52 [] copy_process+0x2c3/0x1398 [] do_fork+0xa8/0x260 [] ? trace_preempt_on+0x2a/0x2f [] ? trace_hardirqs_on_thunk+0x3a/0x3f [] ? sysret_check+0x1b/0x56 [] ? sysret_check+0x1b/0x56 [] SyS_clone+0x16/0x18 [] stub_clone+0x69/0x90 [] ? system_call_fastpath+0x16/0x1b ---[ end trace 8b157a9d20ca1aa2 ]--- in fork.c: #ifdef CONFIG_PROVE_LOCKING DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled); <-- bug here DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled); #endif Cc: Seiji Aguchi Signed-off-by: Steven Rostedt --- arch/x86/include/asm/desc.h | 10 ++++------ arch/x86/kernel/tracepoint.c | 4 ++++ 2 files changed, 8 insertions(+), 6 deletions(-) diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h index 1377ecb29d8d..b90e5dfeee46 100644 --- a/arch/x86/include/asm/desc.h +++ b/arch/x86/include/asm/desc.h @@ -497,21 +497,19 @@ static inline void load_trace_idt(void) #endif /* - * the load_current_idt() is called with interrupt disabled by local_irq_save() + * The load_current_idt() must be called with interrupts disabled * to avoid races. That way the IDT will always be set back to the expected - * descriptor. + * descriptor. It's also called when a CPU is being initialized, and + * that doesn't need to disable interrupts, as nothing should be + * bothering the CPU then. */ static inline void load_current_idt(void) { - unsigned long flags; - - local_irq_save(flags); if (is_debug_idt_enabled()) load_debug_idt(); else if (is_trace_idt_enabled()) load_trace_idt(); else load_idt((const struct desc_ptr *)&idt_descr); - local_irq_restore(flags); } #endif /* _ASM_X86_DESC_H */ diff --git a/arch/x86/kernel/tracepoint.c b/arch/x86/kernel/tracepoint.c index 1423efe98fbc..4e584a8d6edd 100644 --- a/arch/x86/kernel/tracepoint.c +++ b/arch/x86/kernel/tracepoint.c @@ -29,7 +29,11 @@ static void set_trace_idt_ctr(int val) static void switch_idt(void *arg) { + unsigned long flags; + + local_irq_save(flags); load_current_idt(); + local_irq_restore(flags); } void trace_irq_vector_regfunc(void) -- 2.20.1