On Tue, Sep 25, 2012 at 11:36:54AM -0700, Paul E. McKenney wrote: > On Tue, Sep 25, 2012 at 08:28:23PM +0200, Sasha Levin wrote: > > On 09/25/2012 02:06 PM, Frederic Weisbecker wrote: > > > Sasha, sorry to burden you with more testing request. > > > Could you please try out this new branch? It includes some fixes after Wu > > > Fenguang and > > > Dan Carpenter reports (not related to your warnings though) and a patch > > > on the top > > > of the pile to ensure I diagnosed well the problem, which return > > > immediately from > > > rcu_user_*() APIs if we are in an interrupt. > > > > > > This way we'll have a clearer view. I also would like to know if there > > > are other > > > problems with the rcu user mode. > > > > > > Thanks! > > > > Alrighty, I don't see any warnings anymore. > > > > I'll keep everything running just in case. > > Very good news!!! Thank you both!!!
So, I've pushed the fixes in a new branch. Changes are: * Added in_interrupt() checks in "rcu: New rcu_user_enter() and rcu_user_exit() APIs" so that rcu_user_enter/exit() don't nest in rcu_irq_enter/exit(). We'll need a longer term solution I guess because of: - Irq bad nesting - An exception could happen in the middle of irq_exit(), although that's quite unlikely (ie: between sub_preempt_count(HARDIRQ) and add_preempt_count(SOFTIRQ) or between sub_preempt_count(SOFTIRQ or HARDIRQ) and rcu_irq_exit(). May be I should rather check for (rdtp->dynticks_nesting & (DYNTICK_TASK_FLAG -1)) to find out if we are in the middle of an irq from an RCU POV. * Fix the !notifie_die(...) == NOTIFY_STOP to become notifie_die(...) != NOTIFY_STOP. Reported by Wu Fenguang and Dan Carpenter. Fixes are folded inside: "x86: Exception hooks for userspace RCU extended QS". The branch (rebase on top of your rcu/idle) is: git://github.com/fweisbec/linux-dynticks.git rcu/idle-for-v3.7-take5 Diff against your rcu/idle: diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index cb20776..3789675 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -232,8 +232,8 @@ DO_ERROR_INFO(X86_TRAP_AC, SIGBUS, "alignment check", alignment_check, dotraplinkage void do_stack_segment(struct pt_regs *regs, long error_code) { exception_enter(regs); - if (!notify_die(DIE_TRAP, "stack segment", regs, error_code, - X86_TRAP_SS, SIGBUS) == NOTIFY_STOP) { + if (notify_die(DIE_TRAP, "stack segment", regs, error_code, + X86_TRAP_SS, SIGBUS) != NOTIFY_STOP) { preempt_conditional_sti(regs); do_trap(X86_TRAP_SS, SIGBUS, "stack segment", regs, error_code, NULL); preempt_conditional_cli(regs); @@ -285,8 +285,8 @@ do_general_protection(struct pt_regs *regs, long error_code) tsk->thread.error_code = error_code; tsk->thread.trap_nr = X86_TRAP_GP; - if (!notify_die(DIE_GPF, "general protection fault", regs, error_code, - X86_TRAP_GP, SIGSEGV) == NOTIFY_STOP) + if (notify_die(DIE_GPF, "general protection fault", regs, error_code, + X86_TRAP_GP, SIGSEGV) != NOTIFY_STOP) die("general protection fault", regs, error_code); goto exit; } @@ -678,8 +678,8 @@ dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code) info.si_errno = 0; info.si_code = ILL_BADSTK; info.si_addr = NULL; - if (!notify_die(DIE_TRAP, "iret exception", regs, error_code, - X86_TRAP_IRET, SIGILL) == NOTIFY_STOP) { + if (notify_die(DIE_TRAP, "iret exception", regs, error_code, + X86_TRAP_IRET, SIGILL) != NOTIFY_STOP) { do_trap(X86_TRAP_IRET, SIGILL, "iret exception", regs, error_code, &info); } diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 72453cf..4fb2376 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -418,6 +418,17 @@ void rcu_user_enter(void) unsigned long flags; struct rcu_dynticks *rdtp; + /* + * Some contexts may involve an exception occuring in an irq, + * leading to that nesting: + * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit() + * This would mess up the dyntick_nesting count though. And rcu_irq_*() + * helpers are enough to protect RCU uses inside the exception. So + * just return immediately if we detect we are in an IRQ. + */ + if (in_interrupt()) + return; + WARN_ON_ONCE(!current->mm); local_irq_save(flags); @@ -566,6 +577,17 @@ void rcu_user_exit(void) unsigned long flags; struct rcu_dynticks *rdtp; + /* + * Some contexts may involve an exception occuring in an irq, + * leading to that nesting: + * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit() + * This would mess up the dyntick_nesting count though. And rcu_irq_*() + * helpers are enough to protect RCU uses inside the exception. So + * just return immediately if we detect we are in an IRQ. + */ + if (in_interrupt()) + return; + local_irq_save(flags); rdtp = &__get_cpu_var(rcu_dynticks); if (rdtp->in_user) { -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/