Messages in this thread | | | Date | Sat, 31 Jan 2015 08:18:50 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] x86, traps: Fix ist_enter from userspace |
| |
On Sat, Jan 31, 2015 at 05:01:34AM -0800, Andy Lutomirski wrote: > context_tracking_user_exit() has no effect if in_interrupt() returns true, > so ist_enter() didn't work. Fix it by calling exception_enter(), and thus > context_tracking_user_exit(), before incrementing the preempt count. > > This also adds an assertion that will catch the problem reliably if > CONFIG_PROVE_RCU=y to help prevent the bug from being reintroduced. > > Fixes: 959274753857 x86, traps: Track entry into and exit from IST context > Reported-by: Sasha Levin <sasha.levin@oracle.com> > Signed-off-by: Andy Lutomirski <luto@amacapital.net> > --- > arch/x86/kernel/traps.c | 25 ++++++++++++++++++------- > 1 file changed, 18 insertions(+), 7 deletions(-) > > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c > index 7176f84f95a4..c74f2f5652da 100644 > --- a/arch/x86/kernel/traps.c > +++ b/arch/x86/kernel/traps.c > @@ -110,15 +110,11 @@ static inline void preempt_conditional_cli(struct pt_regs *regs) > > enum ctx_state ist_enter(struct pt_regs *regs) > { > - /* > - * We are atomic because we're on the IST stack (or we're on x86_32, > - * in which case we still shouldn't schedule. > - */ > - preempt_count_add(HARDIRQ_OFFSET); > + enum ctx_state prev_state; > > if (user_mode_vm(regs)) { > /* Other than that, we're just an exception. */ > - return exception_enter(); > + prev_state = exception_enter(); > } else { > /* > * We might have interrupted pretty much anything. In > @@ -127,12 +123,27 @@ enum ctx_state ist_enter(struct pt_regs *regs) > * but we need to notify RCU. > */ > rcu_nmi_enter(); > - return IN_KERNEL; /* the value is irrelevant. */ > + prev_state = IN_KERNEL; /* the value is irrelevant. */ > } > + > + /* > + * We are atomic because we're on the IST stack (or we're on x86_32, > + * in which case we still shouldn't schedule). > + * > + * This must be after exception_enter(), because exception_enter() > + * won't do anything if in_interrupt() returns true. > + */ > + preempt_count_add(HARDIRQ_OFFSET);
So the reason we need this here is that ist_exit() does not have access to the bits tested by user_mode_vm()? Or is the idea to avoid an additional test in ist_exit()? (Wondering why this isn't in the above "else" clause.)
Thanx, Paul
> + > + /* This code is a bit fragile. Test it. */ > + rcu_lockdep_assert(rcu_is_watching(), "ist_enter didn't work"); > + > + return prev_state; > } > > void ist_exit(struct pt_regs *regs, enum ctx_state prev_state) > { > + /* Must be before exception_exit. */ > preempt_count_sub(HARDIRQ_OFFSET); > > if (user_mode_vm(regs)) > -- > 2.1.0 >
| |