On Mon, Nov 21, 2022 at 11:57:03AM -0800, Paul E. McKenney wrote: > On Sat, Nov 19, 2022 at 12:00:49PM +0800, Zheng Yejian wrote: > > Register kprobe on __rcu_irq_enter_check_tick() can cause kernel stack > > overflow [1]. This issue is first found in v5.10 and can be reproduced > > by enabling CONFIG_NO_HZ_FULL and doing like: > > # cd /sys/kernel/debug/tracing/ > > # echo 'p:mp1 __rcu_irq_enter_check_tick' >> kprobe_events > > # echo 1 > events/kprobes/enable > > > > So __rcu_irq_enter_check_tick() should not be kprobed, mark it as noinstr. > > Good catch! > > I am inclined to queue this, but noticed that one of its callers need > it to be noinstr but that the others do not. > > Need noinstr: > > o enter_from_kernel_mode() -> __enter_from_kernel_mode() -> > rcu_irq_enter_check_tick() -> __rcu_irq_enter_check_tick() > > Doesn't need noinstr: > > o ct_nmi_enter() -> rcu_irq_enter_check_tick() -> > __rcu_irq_enter_check_tick(), courtesy of the call to > instrumentation_begin() in ct_nmi_enter() that precedes the call > to rcu_irq_enter_check_tick(). > > o irqentry_enter() -> rcu_irq_enter_check_tick() -> > __rcu_irq_enter_check_tick(), courtesy of the call to > instrumentation_begin() in irqentry_enter() that precedes the > call to rcu_irq_enter_check_tick(). > > Is tagging __rcu_irq_enter_check_tick() with noinstr as > proposed in this patch the right thing to do, or should there > be calls to instrumentation_begin() and instrumentation_end() in > enter_from_kernel_mode()? Or something else entirely? Tagging as noinstr doesn't look right as there are functions in __rcu_irq_enter_check_tick() that can be traced anyway. Also that function has the constraint that it can't be called while RCU is idle so it's up to the caller to call instrumentation_begin()/end(). Thanks.
