| Message ID | 333cecfe-3045-8e0a-0c08-64ff590845ab@linux.alibaba.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | fix & prevent the missing preemption disabling | expand |
Hi, > diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h > index abe1a50..2bc1522 100644 > --- a/include/linux/trace_recursion.h > +++ b/include/linux/trace_recursion.h > @@ -135,6 +135,9 @@ static __always_inline int trace_get_context_bit(void) > # define do_ftrace_record_recursion(ip, pip) do { } while (0) > #endif > > +/* > + * Preemption is promised to be disabled when return bit > 0. > + */ > static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsigned long pip, > int start) > { > @@ -162,11 +165,17 @@ static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsign > current->trace_recursion = val; > barrier(); > > + preempt_disable_notrace(); > + > return bit; > } > > +/* > + * Preemption will be enabled (if it was previously enabled). > + */ > static __always_inline void trace_clear_recursion(int bit) > { > + preempt_enable_notrace(); > barrier(); > trace_recursion_clear(bit); > } The two comments should be updated too since Steven removed the "bit == 0" trick. > @@ -178,7 +187,7 @@ static __always_inline void trace_clear_recursion(int bit) > * tracing recursed in the same context (normal vs interrupt), > * > * Returns: -1 if a recursion happened. > - * >= 0 if no recursion > + * > 0 if no recursion. > */ > static __always_inline int ftrace_test_recursion_trylock(unsigned long ip, > unsigned long parent_ip) And this change would not be correct now. Regards Miroslav
Hi, Miroslav On 2021/10/26 下午5:35, Miroslav Benes wrote: > Hi, > >> diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h >> index abe1a50..2bc1522 100644 >> --- a/include/linux/trace_recursion.h >> +++ b/include/linux/trace_recursion.h >> @@ -135,6 +135,9 @@ static __always_inline int trace_get_context_bit(void) >> # define do_ftrace_record_recursion(ip, pip) do { } while (0) >> #endif >> >> +/* >> + * Preemption is promised to be disabled when return bit > 0. >> + */ >> static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsigned long pip, >> int start) >> { >> @@ -162,11 +165,17 @@ static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsign >> current->trace_recursion = val; >> barrier(); >> >> + preempt_disable_notrace(); >> + >> return bit; >> } >> >> +/* >> + * Preemption will be enabled (if it was previously enabled). >> + */ >> static __always_inline void trace_clear_recursion(int bit) >> { >> + preempt_enable_notrace(); >> barrier(); >> trace_recursion_clear(bit); >> } > > The two comments should be updated too since Steven removed the "bit == 0" > trick. Could you please give more hint on how will it be correct? I get the point that bit will no longer be 0, there are only -1 or > 0 now so trace_test_and_set_recursion() will disable preemption on bit > 0 and trace_clear_recursion() will enabled it since it should only be called when bit > 0 (I remember we could use a WARN_ON here now :-P). > >> @@ -178,7 +187,7 @@ static __always_inline void trace_clear_recursion(int bit) >> * tracing recursed in the same context (normal vs interrupt), >> * >> * Returns: -1 if a recursion happened. >> - * >= 0 if no recursion >> + * > 0 if no recursion. >> */ >> static __always_inline int ftrace_test_recursion_trylock(unsigned long ip, >> unsigned long parent_ip) > > And this change would not be correct now. I thought it will no longer return 0 so I change it to > 0, isn't that correct? Regards, Michael Wang > > Regards > Miroslav >
On Tue, 26 Oct 2021 17:48:10 +0800 王贇 <yun.wang@linux.alibaba.com> wrote: > > The two comments should be updated too since Steven removed the "bit == 0" > > trick. > > Could you please give more hint on how will it be correct? > > I get the point that bit will no longer be 0, there are only -1 or > 0 now > so trace_test_and_set_recursion() will disable preemption on bit > 0 and > trace_clear_recursion() will enabled it since it should only be called when > bit > 0 (I remember we could use a WARN_ON here now :-P). > > > > >> @@ -178,7 +187,7 @@ static __always_inline void trace_clear_recursion(int bit) > >> * tracing recursed in the same context (normal vs interrupt), > >> * > >> * Returns: -1 if a recursion happened. > >> - * >= 0 if no recursion > >> + * > 0 if no recursion. > >> */ > >> static __always_inline int ftrace_test_recursion_trylock(unsigned long ip, > >> unsigned long parent_ip) > > > > And this change would not be correct now. > > I thought it will no longer return 0 so I change it to > 0, isn't that correct? No it is not. I removed the bit + 1 return value, which means it returns the actual bit now. Which is 0 or more. -- Steve
On 2021/10/26 下午8:01, Steven Rostedt wrote: > On Tue, 26 Oct 2021 17:48:10 +0800 > 王贇 <yun.wang@linux.alibaba.com> wrote: > >>> The two comments should be updated too since Steven removed the "bit == 0" >>> trick. >> >> Could you please give more hint on how will it be correct? >> >> I get the point that bit will no longer be 0, there are only -1 or > 0 now >> so trace_test_and_set_recursion() will disable preemption on bit > 0 and >> trace_clear_recursion() will enabled it since it should only be called when >> bit > 0 (I remember we could use a WARN_ON here now :-P). >> >>> >>>> @@ -178,7 +187,7 @@ static __always_inline void trace_clear_recursion(int bit) >>>> * tracing recursed in the same context (normal vs interrupt), >>>> * >>>> * Returns: -1 if a recursion happened. >>>> - * >= 0 if no recursion >>>> + * > 0 if no recursion. >>>> */ >>>> static __always_inline int ftrace_test_recursion_trylock(unsigned long ip, >>>> unsigned long parent_ip) >>> >>> And this change would not be correct now. >> >> I thought it will no longer return 0 so I change it to > 0, isn't that correct? > > No it is not. I removed the bit + 1 return value, which means it returns the > actual bit now. Which is 0 or more. Ah, the return is bit not val, I must be drunk... My apologize for the stupid comments... I'll send a v6 for this patch only to fix that, please let me know if this is not a good way to fix few lines of comments. Regards, Michael Wang > > -- Steve >
On Wed, 27 Oct 2021 09:54:13 +0800 王贇 <yun.wang@linux.alibaba.com> wrote: > My apologize for the stupid comments... I'll send a v6 for this patch > only to fix that, please let me know if this is not a good way to fix > few lines of comments. Actually, please resend both patches, as a new patch set, on its own thread. Just replying here won't trigger my patchwork scripts. And also, if you don't include the other patch, the scripts will drop it. Thanks, -- Steve
On 2021/10/27 上午10:26, Steven Rostedt wrote: > On Wed, 27 Oct 2021 09:54:13 +0800 > 王贇 <yun.wang@linux.alibaba.com> wrote: > >> My apologize for the stupid comments... I'll send a v6 for this patch >> only to fix that, please let me know if this is not a good way to fix >> few lines of comments. > > Actually, please resend both patches, as a new patch set, on its own thread. > > Just replying here won't trigger my patchwork scripts. > > And also, if you don't include the other patch, the scripts will drop > it. Got it~ Regards, Michael Wang > > Thanks, > > -- Steve >
diff --git a/arch/csky/kernel/probes/ftrace.c b/arch/csky/kernel/probes/ftrace.c index b388228..834cffc 100644 --- a/arch/csky/kernel/probes/ftrace.c +++ b/arch/csky/kernel/probes/ftrace.c @@ -17,7 +17,6 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, return; regs = ftrace_get_regs(fregs); - preempt_disable_notrace(); p = get_kprobe((kprobe_opcode_t *)ip); if (!p) { p = get_kprobe((kprobe_opcode_t *)(ip - MCOUNT_INSN_SIZE)); @@ -57,7 +56,6 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, __this_cpu_write(current_kprobe, NULL); } out: - preempt_enable_notrace(); ftrace_test_recursion_unlock(bit); } NOKPROBE_SYMBOL(kprobe_ftrace_handler); diff --git a/arch/parisc/kernel/ftrace.c b/arch/parisc/kernel/ftrace.c index 7d14242..90c4345 100644 --- a/arch/parisc/kernel/ftrace.c +++ b/arch/parisc/kernel/ftrace.c @@ -210,7 +210,6 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, return; regs = ftrace_get_regs(fregs); - preempt_disable_notrace(); p = get_kprobe((kprobe_opcode_t *)ip); if (unlikely(!p) || kprobe_disabled(p)) goto out; @@ -239,7 +238,6 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, } __this_cpu_write(current_kprobe, NULL); out: - preempt_enable_notrace(); ftrace_test_recursion_unlock(bit); } NOKPROBE_SYMBOL(kprobe_ftrace_handler); diff --git a/arch/powerpc/kernel/kprobes-ftrace.c b/arch/powerpc/kernel/kprobes-ftrace.c index 7154d58..072ebe7 100644 --- a/arch/powerpc/kernel/kprobes-ftrace.c +++ b/arch/powerpc/kernel/kprobes-ftrace.c @@ -26,7 +26,6 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip, return; regs = ftrace_get_regs(fregs); - preempt_disable_notrace(); p = get_kprobe((kprobe_opcode_t *)nip); if (unlikely(!p) || kprobe_disabled(p)) goto out; @@ -61,7 +60,6 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip, __this_cpu_write(current_kprobe, NULL); } out: - preempt_enable_notrace(); ftrace_test_recursion_unlock(bit); } NOKPROBE_SYMBOL(kprobe_ftrace_handler); diff --git a/arch/riscv/kernel/probes/ftrace.c b/arch/riscv/kernel/probes/ftrace.c index aab85a8..7142ec4 100644 --- a/arch/riscv/kernel/probes/ftrace.c +++ b/arch/riscv/kernel/probes/ftrace.c @@ -15,7 +15,6 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, if (bit < 0) return; - preempt_disable_notrace(); p = get_kprobe((kprobe_opcode_t *)ip); if (unlikely(!p) || kprobe_disabled(p)) goto out; @@ -52,7 +51,6 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, __this_cpu_write(current_kprobe, NULL); } out: - preempt_enable_notrace(); ftrace_test_recursion_unlock(bit); } NOKPROBE_SYMBOL(kprobe_ftrace_handler); diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c index 596de2f..dd2ec14 100644 --- a/arch/x86/kernel/kprobes/ftrace.c +++ b/arch/x86/kernel/kprobes/ftrace.c @@ -25,7 +25,6 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, if (bit < 0) return; - preempt_disable_notrace(); p = get_kprobe((kprobe_opcode_t *)ip); if (unlikely(!p) || kprobe_disabled(p)) goto out; @@ -59,7 +58,6 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, __this_cpu_write(current_kprobe, NULL); } out: - preempt_enable_notrace(); ftrace_test_recursion_unlock(bit); } NOKPROBE_SYMBOL(kprobe_ftrace_handler); diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h index abe1a50..2bc1522 100644 --- a/include/linux/trace_recursion.h +++ b/include/linux/trace_recursion.h @@ -135,6 +135,9 @@ static __always_inline int trace_get_context_bit(void) # define do_ftrace_record_recursion(ip, pip) do { } while (0) #endif +/* + * Preemption is promised to be disabled when return bit > 0. + */ static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsigned long pip, int start) { @@ -162,11 +165,17 @@ static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsign current->trace_recursion = val; barrier(); + preempt_disable_notrace(); + return bit; } +/* + * Preemption will be enabled (if it was previously enabled). + */ static __always_inline void trace_clear_recursion(int bit) { + preempt_enable_notrace(); barrier(); trace_recursion_clear(bit); } @@ -178,7 +187,7 @@ static __always_inline void trace_clear_recursion(int bit) * tracing recursed in the same context (normal vs interrupt), * * Returns: -1 if a recursion happened. - * >= 0 if no recursion + * > 0 if no recursion. */ static __always_inline int ftrace_test_recursion_trylock(unsigned long ip, unsigned long parent_ip) diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c index e8029ae..b8d75fb 100644 --- a/kernel/livepatch/patch.c +++ b/kernel/livepatch/patch.c @@ -49,14 +49,16 @@ static void notrace klp_ftrace_handler(unsigned long ip, ops = container_of(fops, struct klp_ops, fops); + /* + * + * The ftrace_test_recursion_trylock() will disable preemption, + * which is required for the variant of synchronize_rcu() that is + * used to allow patching functions where RCU is not watching. + * See klp_synchronize_transition() for more details. + */ bit = ftrace_test_recursion_trylock(ip, parent_ip); if (WARN_ON_ONCE(bit < 0)) return; - /* - * A variant of synchronize_rcu() is used to allow patching functions - * where RCU is not watching, see klp_synchronize_transition(). - */ - preempt_disable_notrace(); func = list_first_or_null_rcu(&ops->func_stack, struct klp_func, stack_node); @@ -120,7 +122,6 @@ static void notrace klp_ftrace_handler(unsigned long ip, klp_arch_set_pc(fregs, (unsigned long)func->new_func); unlock: - preempt_enable_notrace(); ftrace_test_recursion_unlock(bit); } diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index b7be1df..7392bc7 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -7198,16 +7198,15 @@ void ftrace_reset_array_ops(struct trace_array *tr) struct ftrace_ops *op; int bit; + /* + * The ftrace_test_and_set_recursion() will disable preemption, + * which is required since some of the ops may be dynamically + * allocated, they must be freed after a synchronize_rcu(). + */ bit = trace_test_and_set_recursion(ip, parent_ip, TRACE_LIST_START); if (bit < 0) return; - /* - * Some of the ops may be dynamically allocated, - * they must be freed after a synchronize_rcu(). - */ - preempt_disable_notrace(); - do_for_each_ftrace_op(op, ftrace_ops_list) { /* Stub functions don't need to be called nor tested */ if (op->flags & FTRACE_OPS_FL_STUB) @@ -7231,7 +7230,6 @@ void ftrace_reset_array_ops(struct trace_array *tr) } } while_for_each_ftrace_op(op); out: - preempt_enable_notrace(); trace_clear_recursion(bit); } @@ -7279,12 +7277,9 @@ static void ftrace_ops_assist_func(unsigned long ip, unsigned long parent_ip, if (bit < 0) return; - preempt_disable_notrace(); - if (!(op->flags & FTRACE_OPS_FL_RCU) || rcu_is_watching()) op->func(ip, parent_ip, op, fregs); - preempt_enable_notrace(); trace_clear_recursion(bit); } NOKPROBE_SYMBOL(ftrace_ops_assist_func); diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c index 1f0e63f..9f1bfbe 100644 --- a/kernel/trace/trace_functions.c +++ b/kernel/trace/trace_functions.c @@ -186,7 +186,6 @@ static void function_trace_start(struct trace_array *tr) return; trace_ctx = tracing_gen_ctx(); - preempt_disable_notrace(); cpu = smp_processor_id(); data = per_cpu_ptr(tr->array_buffer.data, cpu); @@ -194,7 +193,6 @@ static void function_trace_start(struct trace_array *tr) trace_function(tr, ip, parent_ip, trace_ctx); ftrace_test_recursion_unlock(bit); - preempt_enable_notrace(); } #ifdef CONFIG_UNWINDER_ORC @@ -298,8 +296,6 @@ static inline void process_repeats(struct trace_array *tr, if (bit < 0) return; - preempt_disable_notrace(); - cpu = smp_processor_id(); data = per_cpu_ptr(tr->array_buffer.data, cpu); if (atomic_read(&data->disabled)) @@ -324,7 +320,6 @@ static inline void process_repeats(struct trace_array *tr, out: ftrace_test_recursion_unlock(bit); - preempt_enable_notrace(); } static void
As the documentation explained, ftrace_test_recursion_trylock() and ftrace_test_recursion_unlock() were supposed to disable and enable preemption properly, however currently this work is done outside of the function, which could be missing by mistake. And since the internal using of trace_test_and_set_recursion() and trace_clear_recursion() also require preemption disabled, we can just merge the logical. This patch will make sure the preemption has been disabled when trace_test_and_set_recursion() return bit >= 0, and trace_clear_recursion() will enable the preemption if previously enabled. CC: Petr Mladek <pmladek@suse.com> CC: Steven Rostedt <rostedt@goodmis.org> CC: Miroslav Benes <mbenes@suse.cz> Reported-by: Abaci <abaci@linux.alibaba.com> Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Michael Wang <yun.wang@linux.alibaba.com> --- arch/csky/kernel/probes/ftrace.c | 2 -- arch/parisc/kernel/ftrace.c | 2 -- arch/powerpc/kernel/kprobes-ftrace.c | 2 -- arch/riscv/kernel/probes/ftrace.c | 2 -- arch/x86/kernel/kprobes/ftrace.c | 2 -- include/linux/trace_recursion.h | 11 ++++++++++- kernel/livepatch/patch.c | 13 +++++++------ kernel/trace/ftrace.c | 15 +++++---------- kernel/trace/trace_functions.c | 5 ----- 9 files changed, 22 insertions(+), 32 deletions(-)