From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com> To: Mark Rutland <mark.rutland@arm.com> Cc: broonie@kernel.org, jpoimboe@redhat.com, ardb@kernel.org, nobuta.keiya@fujitsu.com, sjitindarsingh@gmail.com, catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org, pasha.tatashin@soleen.com, jthierry@redhat.com, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v6 1/3] arm64: Improve the unwinder return value Date: Thu, 29 Jul 2021 08:54:58 -0500 [thread overview] Message-ID: <52686cb6-573c-03ca-06c2-67ae07c91243@linux.microsoft.com> (raw) In-Reply-To: <20210728165635.GA47345@C02TD0UTHF1T.local> Thanks for the review. Responses inline... On 7/28/21 11:56 AM, Mark Rutland wrote: > On Wed, Jun 30, 2021 at 05:33:54PM -0500, madvenka@linux.microsoft.com wrote: >> From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com> >> >> Currently, the unwinder returns a tri-state return value: >> >> 0 means "continue with the unwind" >> -ENOENT means "successful termination of the stack trace" >> -EINVAL means "fatal error, abort the stack trace" >> >> This is confusing. To fix this, define an enumeration of different return >> codes to make it clear. Handle the return codes in all of the unwind >> consumers. > > I agree the tri-state is confusing, and I also generally agree that > enums are preferabel to a set of error codes. However, I don't think > this is quite the right abstraction; more on that below. > OK. >> >> Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com> >> --- >> arch/arm64/include/asm/stacktrace.h | 14 ++++++-- >> arch/arm64/kernel/perf_callchain.c | 5 ++- >> arch/arm64/kernel/process.c | 8 +++-- >> arch/arm64/kernel/return_address.c | 10 ++++-- >> arch/arm64/kernel/stacktrace.c | 53 ++++++++++++++++------------- >> arch/arm64/kernel/time.c | 9 +++-- >> 6 files changed, 64 insertions(+), 35 deletions(-) >> >> diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h >> index eb29b1fe8255..6fcd58553fb1 100644 >> --- a/arch/arm64/include/asm/stacktrace.h >> +++ b/arch/arm64/include/asm/stacktrace.h >> @@ -30,6 +30,12 @@ struct stack_info { >> enum stack_type type; >> }; >> >> +enum unwind_rc { >> + UNWIND_CONTINUE, /* No errors encountered */ >> + UNWIND_ABORT, /* Fatal errors encountered */ >> + UNWIND_FINISH, /* End of stack reached successfully */ >> +}; > > Generally, there are a bunch of properties we might need to check for an > unwind step relating to reliabiltiy (e.g. as you add > UNWIND_CONTINUE_WITH_RISK in the next patch), and I'd prefer that we > check those properties on the struct stackframe, and simplify > unwind_frame() to return a bool. > > Something akin to the x86 unwinders, where the main loop looks like: > > for (unwind_start(&state, ...); > !unwind_done(&state) && !unwind_error(&state); > unwind_next_frame(&state) { > ... > } > > That way we don't have to grow the enum to handle every variation that > we can think of, and it's simple enough for users to check the > properties with the helpers. > I can do that. >> + >> /* >> * A snapshot of a frame record or fp/lr register values, along with some >> * accounting information necessary for robust unwinding. >> @@ -61,7 +67,8 @@ struct stackframe { >> #endif >> }; >> >> -extern int unwind_frame(struct task_struct *tsk, struct stackframe *frame); >> +extern enum unwind_rc unwind_frame(struct task_struct *tsk, >> + struct stackframe *frame); >> extern void walk_stackframe(struct task_struct *tsk, struct stackframe *frame, >> bool (*fn)(void *, unsigned long), void *data); >> extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk, >> @@ -148,8 +155,8 @@ static inline bool on_accessible_stack(const struct task_struct *tsk, >> return false; >> } >> >> -static inline void start_backtrace(struct stackframe *frame, >> - unsigned long fp, unsigned long pc) >> +static inline enum unwind_rc start_backtrace(struct stackframe *frame, >> + unsigned long fp, unsigned long pc) >> { >> frame->fp = fp; >> frame->pc = pc; >> @@ -169,6 +176,7 @@ static inline void start_backtrace(struct stackframe *frame, >> bitmap_zero(frame->stacks_done, __NR_STACK_TYPES); >> frame->prev_fp = 0; >> frame->prev_type = STACK_TYPE_UNKNOWN; >> + return UNWIND_CONTINUE; >> } >> >> #endif /* __ASM_STACKTRACE_H */ >> diff --git a/arch/arm64/kernel/perf_callchain.c b/arch/arm64/kernel/perf_callchain.c >> index 88ff471b0bce..f459208149ae 100644 >> --- a/arch/arm64/kernel/perf_callchain.c >> +++ b/arch/arm64/kernel/perf_callchain.c >> @@ -148,13 +148,16 @@ void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, >> struct pt_regs *regs) >> { >> struct stackframe frame; >> + enum unwind_rc rc; >> >> if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) { >> /* We don't support guest os callchain now */ >> return; >> } >> >> - start_backtrace(&frame, regs->regs[29], regs->pc); >> + rc = start_backtrace(&frame, regs->regs[29], regs->pc); >> + if (rc == UNWIND_FINISH || rc == UNWIND_ABORT) >> + return; >> walk_stackframe(current, &frame, callchain_trace, entry); > > As a first step, could we convert this over to arch_stack_walk()? > OK. >> } >> >> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c >> index 6e60aa3b5ea9..e9c763b44fd4 100644 >> --- a/arch/arm64/kernel/process.c >> +++ b/arch/arm64/kernel/process.c >> @@ -573,6 +573,7 @@ unsigned long get_wchan(struct task_struct *p) >> struct stackframe frame; >> unsigned long stack_page, ret = 0; >> int count = 0; >> + enum unwind_rc rc; >> if (!p || p == current || p->state == TASK_RUNNING) >> return 0; >> >> @@ -580,10 +581,13 @@ unsigned long get_wchan(struct task_struct *p) >> if (!stack_page) >> return 0; >> >> - start_backtrace(&frame, thread_saved_fp(p), thread_saved_pc(p)); >> + rc = start_backtrace(&frame, thread_saved_fp(p), thread_saved_pc(p)); >> + if (rc == UNWIND_FINISH || rc == UNWIND_ABORT) >> + return 0; >> >> do { >> - if (unwind_frame(p, &frame)) >> + rc = unwind_frame(p, &frame); >> + if (rc == UNWIND_FINISH || rc == UNWIND_ABORT) >> goto out; >> if (!in_sched_functions(frame.pc)) { >> ret = frame.pc; > > Likewise, can we convert this to use arch_stack_walk()? > OK. >> diff --git a/arch/arm64/kernel/return_address.c b/arch/arm64/kernel/return_address.c >> index a6d18755652f..1224e043e98f 100644 >> --- a/arch/arm64/kernel/return_address.c >> +++ b/arch/arm64/kernel/return_address.c >> @@ -36,13 +36,17 @@ void *return_address(unsigned int level) >> { >> struct return_address_data data; >> struct stackframe frame; >> + enum unwind_rc rc; >> >> data.level = level + 2; >> data.addr = NULL; >> >> - start_backtrace(&frame, >> - (unsigned long)__builtin_frame_address(0), >> - (unsigned long)return_address); >> + rc = start_backtrace(&frame, >> + (unsigned long)__builtin_frame_address(0), >> + (unsigned long)return_address); >> + if (rc == UNWIND_FINISH || rc == UNWIND_ABORT) >> + return NULL; >> + >> walk_stackframe(current, &frame, save_return_addr, &data); > > Likewise, can we convert this to use arch_stack_walk()? > OK. Thanks. Madhavan _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-07-29 13:57 UTC|newest] Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <3f2aab69a35c243c5e97f47c4ad84046355f5b90> 2021-06-30 22:33 ` [RFC PATCH v6 0/3] arm64: Implement stack trace reliability checks madvenka 2021-06-30 22:33 ` [RFC PATCH v6 1/3] arm64: Improve the unwinder return value madvenka 2021-07-28 16:56 ` Mark Rutland 2021-07-29 13:54 ` Madhavan T. Venkataraman [this message] 2021-06-30 22:33 ` [RFC PATCH v6 2/3] arm64: Introduce stack trace reliability checks in the unwinder madvenka 2021-06-30 22:33 ` [RFC PATCH v6 3/3] arm64: Create a list of SYM_CODE functions, check return PC against list madvenka 2021-07-28 17:25 ` Mark Rutland 2021-07-29 14:06 ` Madhavan T. Venkataraman 2021-07-29 14:52 ` Mark Brown 2021-07-29 17:07 ` Madhavan T. Venkataraman 2021-07-29 15:48 ` Mark Rutland 2021-07-29 16:27 ` Mark Brown 2021-07-29 17:09 ` Madhavan T. Venkataraman 2021-07-26 13:49 ` [RFC PATCH v6 0/3] arm64: Implement stack trace reliability checks Madhavan T. Venkataraman 2021-08-12 13:24 ` [RFC PATCH v7 0/4] arm64: Reorganize the unwinder and implement " madvenka 2021-08-12 13:24 ` [RFC PATCH v7 1/4] arm64: Make all stack walking functions use arch_stack_walk() madvenka 2021-08-12 15:23 ` Mark Brown 2021-08-12 16:30 ` Madhavan T. Venkataraman 2021-08-12 13:24 ` [RFC PATCH v7 2/4] arm64: Reorganize the unwinder code for better consistency and maintenance madvenka 2021-08-12 13:24 ` [RFC PATCH v7 3/4] arm64: Introduce stack trace reliability checks in the unwinder madvenka 2021-08-12 13:24 ` [RFC PATCH v7 4/4] arm64: Create a list of SYM_CODE functions, check return PC against list madvenka 2021-08-12 18:31 ` [RFC PATCH v7 0/4] arm64: Reorganize the unwinder and implement stack trace reliability checks Madhavan T. Venkataraman 2021-08-12 18:45 ` Madhavan T. Venkataraman 2021-08-12 18:35 ` madvenka 2021-08-12 18:35 ` [RFC PATCH v7 1/4] arm64: Make all stack walking functions use arch_stack_walk() madvenka 2021-08-12 18:35 ` [RFC PATCH v7 2/4] arm64: Reorganize the unwinder code for better consistency and maintenance madvenka 2021-08-12 18:35 ` [RFC PATCH v7 3/4] arm64: Introduce stack trace reliability checks in the unwinder madvenka 2021-08-12 18:35 ` [RFC PATCH v7 4/4] arm64: Create a list of SYM_CODE functions, check return PC against list madvenka
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