| Message ID | 156404257493.2020.7940525305482369976.stgit@devnote2 (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: kprobes: Fix some bugs in arm64 kprobes | expand |
On Thu, Jul 25, 2019 at 05:16:15PM +0900, Masami Hiramatsu wrote: > Make debug exceptions visible from RCU so that synchronize_rcu() > correctly track the debug exception handler. > > This also introduces sanity checks for user-mode exceptions as same > as x86's ist_enter()/ist_exit(). > > The debug exception can interrupt in idle task. For example, it warns > if we put a kprobe on a function called from idle task as below. > The warning message showed that the rcu_read_lock() caused this > problem. But actually, this means the RCU is lost the context which > is already in NMI/IRQ. > > /sys/kernel/debug/tracing # echo p default_idle_call >> kprobe_events > /sys/kernel/debug/tracing # echo 1 > events/kprobes/enable > /sys/kernel/debug/tracing # [ 135.122237] > [ 135.125035] ============================= > [ 135.125310] WARNING: suspicious RCU usage > [ 135.125581] 5.2.0-08445-g9187c508bdc7 #20 Not tainted > [ 135.125904] ----------------------------- > [ 135.126205] include/linux/rcupdate.h:594 rcu_read_lock() used illegally while idle! > [ 135.126839] > [ 135.126839] other info that might help us debug this: > [ 135.126839] > [ 135.127410] > [ 135.127410] RCU used illegally from idle CPU! > [ 135.127410] rcu_scheduler_active = 2, debug_locks = 1 > [ 135.128114] RCU used illegally from extended quiescent state! > [ 135.128555] 1 lock held by swapper/0/0: > [ 135.128944] #0: (____ptrval____) (rcu_read_lock){....}, at: call_break_hook+0x0/0x178 > [ 135.130499] > [ 135.130499] stack backtrace: > [ 135.131192] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.2.0-08445-g9187c508bdc7 #20 > [ 135.131841] Hardware name: linux,dummy-virt (DT) > [ 135.132224] Call trace: > [ 135.132491] dump_backtrace+0x0/0x140 > [ 135.132806] show_stack+0x24/0x30 > [ 135.133133] dump_stack+0xc4/0x10c > [ 135.133726] lockdep_rcu_suspicious+0xf8/0x108 > [ 135.134171] call_break_hook+0x170/0x178 > [ 135.134486] brk_handler+0x28/0x68 > [ 135.134792] do_debug_exception+0x90/0x150 > [ 135.135051] el1_dbg+0x18/0x8c > [ 135.135260] default_idle_call+0x0/0x44 > [ 135.135516] cpu_startup_entry+0x2c/0x30 > [ 135.135815] rest_init+0x1b0/0x280 > [ 135.136044] arch_call_rest_init+0x14/0x1c > [ 135.136305] start_kernel+0x4d4/0x500 > [ 135.136597] > > So make debug exception visible to RCU can fix this warning. > > Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org> > Acked-by: Paul E. McKenney <paulmck@linux.ibm.com> > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> > --- > Changes in v3: > - Make a comment for debug_exception_enter() clearer. > --- > arch/arm64/mm/fault.c | 40 ++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 40 insertions(+) > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > index 9568c116ac7f..ed6c55c87fdc 100644 > --- a/arch/arm64/mm/fault.c > +++ b/arch/arm64/mm/fault.c > @@ -777,6 +777,42 @@ void __init hook_debug_fault_code(int nr, > debug_fault_info[nr].name = name; > } > > +/* > + * In debug exception context, we explicitly disable preemption. Maybe add "despite having interrupts disabled"? > + * This serves two purposes: it makes it much less likely that we would > + * accidentally schedule in exception context and it will force a warning > + * if we somehow manage to schedule by accident. > + */ > +static void debug_exception_enter(struct pt_regs *regs) > +{ > + if (user_mode(regs)) { > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); > + } else { > + /* > + * We might have interrupted pretty much anything. In > + * fact, if we're a debug exception, we can even interrupt > + * NMI processing. We don't want this code makes in_nmi() > + * to return true, but we need to notify RCU. > + */ > + rcu_nmi_enter(); > + } > + > + preempt_disable(); If you're addingt new functions for entry/exit, maybe move the trace_hardirqs_{on,off}() calls in here too? Will
Hi Will, On Wed, 31 Jul 2019 18:26:03 +0100 Will Deacon <will@kernel.org> wrote: > On Thu, Jul 25, 2019 at 05:16:15PM +0900, Masami Hiramatsu wrote: > > Make debug exceptions visible from RCU so that synchronize_rcu() > > correctly track the debug exception handler. > > > > This also introduces sanity checks for user-mode exceptions as same > > as x86's ist_enter()/ist_exit(). > > > > The debug exception can interrupt in idle task. For example, it warns > > if we put a kprobe on a function called from idle task as below. > > The warning message showed that the rcu_read_lock() caused this > > problem. But actually, this means the RCU is lost the context which > > is already in NMI/IRQ. > > > > /sys/kernel/debug/tracing # echo p default_idle_call >> kprobe_events > > /sys/kernel/debug/tracing # echo 1 > events/kprobes/enable > > /sys/kernel/debug/tracing # [ 135.122237] > > [ 135.125035] ============================= > > [ 135.125310] WARNING: suspicious RCU usage > > [ 135.125581] 5.2.0-08445-g9187c508bdc7 #20 Not tainted > > [ 135.125904] ----------------------------- > > [ 135.126205] include/linux/rcupdate.h:594 rcu_read_lock() used illegally while idle! > > [ 135.126839] > > [ 135.126839] other info that might help us debug this: > > [ 135.126839] > > [ 135.127410] > > [ 135.127410] RCU used illegally from idle CPU! > > [ 135.127410] rcu_scheduler_active = 2, debug_locks = 1 > > [ 135.128114] RCU used illegally from extended quiescent state! > > [ 135.128555] 1 lock held by swapper/0/0: > > [ 135.128944] #0: (____ptrval____) (rcu_read_lock){....}, at: call_break_hook+0x0/0x178 > > [ 135.130499] > > [ 135.130499] stack backtrace: > > [ 135.131192] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.2.0-08445-g9187c508bdc7 #20 > > [ 135.131841] Hardware name: linux,dummy-virt (DT) > > [ 135.132224] Call trace: > > [ 135.132491] dump_backtrace+0x0/0x140 > > [ 135.132806] show_stack+0x24/0x30 > > [ 135.133133] dump_stack+0xc4/0x10c > > [ 135.133726] lockdep_rcu_suspicious+0xf8/0x108 > > [ 135.134171] call_break_hook+0x170/0x178 > > [ 135.134486] brk_handler+0x28/0x68 > > [ 135.134792] do_debug_exception+0x90/0x150 > > [ 135.135051] el1_dbg+0x18/0x8c > > [ 135.135260] default_idle_call+0x0/0x44 > > [ 135.135516] cpu_startup_entry+0x2c/0x30 > > [ 135.135815] rest_init+0x1b0/0x280 > > [ 135.136044] arch_call_rest_init+0x14/0x1c > > [ 135.136305] start_kernel+0x4d4/0x500 > > [ 135.136597] > > > > So make debug exception visible to RCU can fix this warning. > > > > Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org> > > Acked-by: Paul E. McKenney <paulmck@linux.ibm.com> > > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> > > --- > > Changes in v3: > > - Make a comment for debug_exception_enter() clearer. > > --- > > arch/arm64/mm/fault.c | 40 ++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 40 insertions(+) > > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > > index 9568c116ac7f..ed6c55c87fdc 100644 > > --- a/arch/arm64/mm/fault.c > > +++ b/arch/arm64/mm/fault.c > > @@ -777,6 +777,42 @@ void __init hook_debug_fault_code(int nr, > > debug_fault_info[nr].name = name; > > } > > > > +/* > > + * In debug exception context, we explicitly disable preemption. > > Maybe add "despite having interrupts disabled"? OK, I'll add it. > > + * This serves two purposes: it makes it much less likely that we would > > + * accidentally schedule in exception context and it will force a warning > > + * if we somehow manage to schedule by accident. > > + */ > > +static void debug_exception_enter(struct pt_regs *regs) > > +{ > > + if (user_mode(regs)) { > > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); > > + } else { > > + /* > > + * We might have interrupted pretty much anything. In > > + * fact, if we're a debug exception, we can even interrupt > > + * NMI processing. We don't want this code makes in_nmi() > > + * to return true, but we need to notify RCU. > > + */ > > + rcu_nmi_enter(); > > + } > > + > > + preempt_disable(); > > If you're addingt new functions for entry/exit, maybe move the > trace_hardirqs_{on,off}() calls in here too? OK, let's move it in these functions. Thank you! > > Will
Hi Masami, On Thu, Aug 01, 2019 at 02:32:25PM +0900, Masami Hiramatsu wrote: > On Wed, 31 Jul 2019 18:26:03 +0100 > Will Deacon <will@kernel.org> wrote: > > On Thu, Jul 25, 2019 at 05:16:15PM +0900, Masami Hiramatsu wrote: > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > > > index 9568c116ac7f..ed6c55c87fdc 100644 > > > --- a/arch/arm64/mm/fault.c > > > +++ b/arch/arm64/mm/fault.c > > > @@ -777,6 +777,42 @@ void __init hook_debug_fault_code(int nr, > > > debug_fault_info[nr].name = name; > > > } > > > > > > +/* > > > + * In debug exception context, we explicitly disable preemption. > > > > Maybe add "despite having interrupts disabled"? > > OK, I'll add it. > > > > + * This serves two purposes: it makes it much less likely that we would > > > + * accidentally schedule in exception context and it will force a warning > > > + * if we somehow manage to schedule by accident. > > > + */ > > > +static void debug_exception_enter(struct pt_regs *regs) > > > +{ > > > + if (user_mode(regs)) { > > > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); > > > + } else { > > > + /* > > > + * We might have interrupted pretty much anything. In > > > + * fact, if we're a debug exception, we can even interrupt > > > + * NMI processing. We don't want this code makes in_nmi() > > > + * to return true, but we need to notify RCU. > > > + */ > > > + rcu_nmi_enter(); > > > + } > > > + > > > + preempt_disable(); > > > > If you're addingt new functions for entry/exit, maybe move the > > trace_hardirqs_{on,off}() calls in here too? > > OK, let's move it in these functions. Brill, thanks. Please just resend this patch, as I can pick the other three up as they are. Will
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 9568c116ac7f..ed6c55c87fdc 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -777,6 +777,42 @@ void __init hook_debug_fault_code(int nr, debug_fault_info[nr].name = name; } +/* + * In debug exception context, we explicitly disable preemption. + * This serves two purposes: it makes it much less likely that we would + * accidentally schedule in exception context and it will force a warning + * if we somehow manage to schedule by accident. + */ +static void debug_exception_enter(struct pt_regs *regs) +{ + if (user_mode(regs)) { + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); + } else { + /* + * We might have interrupted pretty much anything. In + * fact, if we're a debug exception, we can even interrupt + * NMI processing. We don't want this code makes in_nmi() + * to return true, but we need to notify RCU. + */ + rcu_nmi_enter(); + } + + preempt_disable(); + + /* This code is a bit fragile. Test it. */ + RCU_LOCKDEP_WARN(!rcu_is_watching(), "exception_enter didn't work"); +} +NOKPROBE_SYMBOL(debug_exception_enter); + +static void debug_exception_exit(struct pt_regs *regs) +{ + preempt_enable_no_resched(); + + if (!user_mode(regs)) + rcu_nmi_exit(); +} +NOKPROBE_SYMBOL(debug_exception_exit); + #ifdef CONFIG_ARM64_ERRATUM_1463225 DECLARE_PER_CPU(int, __in_cortex_a76_erratum_1463225_wa); @@ -824,6 +860,8 @@ asmlinkage void __exception do_debug_exception(unsigned long addr_if_watchpoint, if (interrupts_enabled(regs)) trace_hardirqs_off(); + debug_exception_enter(regs); + if (user_mode(regs) && !is_ttbr0_addr(pc)) arm64_apply_bp_hardening(); @@ -832,6 +870,8 @@ asmlinkage void __exception do_debug_exception(unsigned long addr_if_watchpoint, inf->sig, inf->code, (void __user *)pc, esr); } + debug_exception_exit(regs); + if (interrupts_enabled(regs)) trace_hardirqs_on(); }
Make debug exceptions visible from RCU so that synchronize_rcu() correctly track the debug exception handler. This also introduces sanity checks for user-mode exceptions as same as x86's ist_enter()/ist_exit(). The debug exception can interrupt in idle task. For example, it warns if we put a kprobe on a function called from idle task as below. The warning message showed that the rcu_read_lock() caused this problem. But actually, this means the RCU is lost the context which is already in NMI/IRQ. /sys/kernel/debug/tracing # echo p default_idle_call >> kprobe_events /sys/kernel/debug/tracing # echo 1 > events/kprobes/enable /sys/kernel/debug/tracing # [ 135.122237] [ 135.125035] ============================= [ 135.125310] WARNING: suspicious RCU usage [ 135.125581] 5.2.0-08445-g9187c508bdc7 #20 Not tainted [ 135.125904] ----------------------------- [ 135.126205] include/linux/rcupdate.h:594 rcu_read_lock() used illegally while idle! [ 135.126839] [ 135.126839] other info that might help us debug this: [ 135.126839] [ 135.127410] [ 135.127410] RCU used illegally from idle CPU! [ 135.127410] rcu_scheduler_active = 2, debug_locks = 1 [ 135.128114] RCU used illegally from extended quiescent state! [ 135.128555] 1 lock held by swapper/0/0: [ 135.128944] #0: (____ptrval____) (rcu_read_lock){....}, at: call_break_hook+0x0/0x178 [ 135.130499] [ 135.130499] stack backtrace: [ 135.131192] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.2.0-08445-g9187c508bdc7 #20 [ 135.131841] Hardware name: linux,dummy-virt (DT) [ 135.132224] Call trace: [ 135.132491] dump_backtrace+0x0/0x140 [ 135.132806] show_stack+0x24/0x30 [ 135.133133] dump_stack+0xc4/0x10c [ 135.133726] lockdep_rcu_suspicious+0xf8/0x108 [ 135.134171] call_break_hook+0x170/0x178 [ 135.134486] brk_handler+0x28/0x68 [ 135.134792] do_debug_exception+0x90/0x150 [ 135.135051] el1_dbg+0x18/0x8c [ 135.135260] default_idle_call+0x0/0x44 [ 135.135516] cpu_startup_entry+0x2c/0x30 [ 135.135815] rest_init+0x1b0/0x280 [ 135.136044] arch_call_rest_init+0x14/0x1c [ 135.136305] start_kernel+0x4d4/0x500 [ 135.136597] So make debug exception visible to RCU can fix this warning. Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org> Acked-by: Paul E. McKenney <paulmck@linux.ibm.com> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> --- Changes in v3: - Make a comment for debug_exception_enter() clearer. --- arch/arm64/mm/fault.c | 40 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 40 insertions(+)