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) {
--
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