| Message ID | 20230702025708.784106-1-guoren@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | riscv: entry: Fixup do_trap_break from kernel side | expand |
| Context | Check | Description |
|---|---|---|
| conchuod/cover_letter | success | Single patches do not need cover letters |
| conchuod/tree_selection | success | Guessed tree name to be fixes at HEAD 533925cb7604 |
| conchuod/fixes_present | success | Fixes tag present in non-next series |
| conchuod/maintainers_pattern | success | MAINTAINERS pattern errors before the patch: 4 and now 4 |
| conchuod/verify_signedoff | success | Signed-off-by tag matches author and committer |
| conchuod/kdoc | success | Errors and warnings before: 0 this patch: 0 |
| conchuod/build_rv64_clang_allmodconfig | success | Errors and warnings before: 8 this patch: 8 |
| conchuod/module_param | success | Was 0 now: 0 |
| conchuod/build_rv64_gcc_allmodconfig | success | Errors and warnings before: 8 this patch: 8 |
| conchuod/build_rv32_defconfig | success | Build OK |
| conchuod/dtb_warn_rv64 | success | Errors and warnings before: 3 this patch: 3 |
| conchuod/header_inline | success | No static functions without inline keyword in header files |
| conchuod/checkpatch | warning | WARNING: Reported-by: should be immediately followed by Closes: with a URL to the report |
| conchuod/build_rv64_nommu_k210_defconfig | success | Build OK |
| conchuod/verify_fixes | success | Fixes tag looks correct |
| conchuod/build_rv64_nommu_virt_defconfig | success | Build OK |
On Sat, Jul 01, 2023 at 10:57:07PM -0400, guoren@kernel.org wrote: > From: Guo Ren <guoren@linux.alibaba.com> > > The irqentry_nmi_enter/exit would force the current context into in_interrupt. > That would trigger the kernel to dead panic, but the kdb still needs "ebreak" to > debug the kernel. > > Move irqentry_nmi_enter/exit to exception_enter/exit could correct handle_break > of the kernel side. <snip> > Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry") > Reported-by: Daniel Thompson <daniel.thompson@linaro.org> > Signed-off-by: Guo Ren <guoren@linux.alibaba.com> > Signed-off-by: Guo Ren <guoren@kernel.org> > Cc: stable@vger.kernel.org I pushed this though the kgdb test suite that originally found the problem (although it didn't occur to me when I reported it that the problem was nothing to do with kgdb ;-) ). So FWIW: Tested-by: Daniel Thompson <daniel.thompson@linaro.org> Daniel.
On Mon, Jul 3, 2023 at 6:29 PM Daniel Thompson <daniel.thompson@linaro.org> wrote: > > On Sat, Jul 01, 2023 at 10:57:07PM -0400, guoren@kernel.org wrote: > > From: Guo Ren <guoren@linux.alibaba.com> > > > > The irqentry_nmi_enter/exit would force the current context into in_interrupt. > > That would trigger the kernel to dead panic, but the kdb still needs "ebreak" to > > debug the kernel. > > > > Move irqentry_nmi_enter/exit to exception_enter/exit could correct handle_break > > of the kernel side. > > <snip> > > > Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry") > > Reported-by: Daniel Thompson <daniel.thompson@linaro.org> > > Signed-off-by: Guo Ren <guoren@linux.alibaba.com> > > Signed-off-by: Guo Ren <guoren@kernel.org> > > Cc: stable@vger.kernel.org > > I pushed this though the kgdb test suite that originally found the > problem (although it didn't occur to me when I reported it that > the problem was nothing to do with kgdb ;-) ). So FWIW: > > Tested-by: Daniel Thompson <daniel.thompson@linaro.org> Thx for the report & tested-by. > > > Daniel.
On Sat, Jul 01, 2023 at 10:57:07PM -0400, guoren@kernel.org wrote: > From: Guo Ren <guoren@linux.alibaba.com> > > The irqentry_nmi_enter/exit would force the current context into in_interrupt. > That would trigger the kernel to dead panic, but the kdb still needs "ebreak" to > debug the kernel. > > Move irqentry_nmi_enter/exit to exception_enter/exit could correct handle_break > of the kernel side. This doesn't explain much if anything :/ I'm confused (probably because I don't know RISC-V very well), what's EBREAK and how does it happen? Specifically, if EBREAK can happen inside an local_irq_disable() region, then the below change is actively wrong. Any exception/interrupt that can happen while local_irq_disable() must be treated like an NMI. If that makes kdb unhappy, fix kdb. > Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry") > Reported-by: Daniel Thompson <daniel.thompson@linaro.org> > Signed-off-by: Guo Ren <guoren@linux.alibaba.com> > Signed-off-by: Guo Ren <guoren@kernel.org> > Cc: stable@vger.kernel.org > --- > arch/riscv/kernel/traps.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c > index efc6b649985a..ed0eb9452f9e 100644 > --- a/arch/riscv/kernel/traps.c > +++ b/arch/riscv/kernel/traps.c > @@ -18,6 +18,7 @@ > #include <linux/irq.h> > #include <linux/kexec.h> > #include <linux/entry-common.h> > +#include <linux/context_tracking.h> > > #include <asm/asm-prototypes.h> > #include <asm/bug.h> > @@ -257,11 +258,11 @@ asmlinkage __visible __trap_section void do_trap_break(struct pt_regs *regs) > > irqentry_exit_to_user_mode(regs); > } else { > - irqentry_state_t state = irqentry_nmi_enter(regs); > + enum ctx_state prev_state = exception_enter(); > > handle_break(regs); > > - irqentry_nmi_exit(regs, state); > + exception_exit(prev_state); > } > } > > -- > 2.36.1 >
On Tue, Jul 04, 2023 at 06:40:03PM +0200, Peter Zijlstra wrote: > On Sat, Jul 01, 2023 at 10:57:07PM -0400, guoren@kernel.org wrote: > > From: Guo Ren <guoren@linux.alibaba.com> > > > > The irqentry_nmi_enter/exit would force the current context into in_interrupt. > > That would trigger the kernel to dead panic, but the kdb still needs "ebreak" to > > debug the kernel. > > > > Move irqentry_nmi_enter/exit to exception_enter/exit could correct handle_break > > of the kernel side. > > This doesn't explain much if anything :/ > > I'm confused (probably because I don't know RISC-V very well), what's > EBREAK and how does it happen? Among other things ebreak is part of the BUG() macro (although it is also used to programmatically enter kgdb). > Specifically, if EBREAK can happen inside an local_irq_disable() region, > then the below change is actively wrong. Any exception/interrupt that > can happen while local_irq_disable() must be treated like an NMI. > > If that makes kdb unhappy, fix kdb. The only relationship this problem has to kgdb/kdb is that is was found using the kgdb test suite. However the panic is absolutely nothing to do with kgdb. I would never normally be so sure regarding the absence of bugs in kgdb but in this case it can be reproduced when kgdb is not enabled in the KConfig which I think puts it in the clear! Reproduction is simply: /bin/echo BUG > /sys/kernel/debug/provoke-crash/DIRECT Above will panic the kernel but, absent options specifically requesting a panic, this should kill the echo process rather than killing the kernel. Daniel.
On Wed, Jul 5, 2023 at 12:40 AM Peter Zijlstra <peterz@infradead.org> wrote: > > On Sat, Jul 01, 2023 at 10:57:07PM -0400, guoren@kernel.org wrote: > > From: Guo Ren <guoren@linux.alibaba.com> > > > > The irqentry_nmi_enter/exit would force the current context into in_interrupt. > > That would trigger the kernel to dead panic, but the kdb still needs "ebreak" to > > debug the kernel. > > > > Move irqentry_nmi_enter/exit to exception_enter/exit could correct handle_break > > of the kernel side. > > This doesn't explain much if anything :/ > > I'm confused (probably because I don't know RISC-V very well), what's > EBREAK and how does it happen? EBREAK is just an instruction of riscv which would rise breakpoint exception. > > Specifically, if EBREAK can happen inside an local_irq_disable() region, > then the below change is actively wrong. Any exception/interrupt that > can happen while local_irq_disable() must be treated like an NMI. When the ebreak happend out of local_irq_disable region, but __nmi_enter forces handle_break() into in_interupt() state. So how about: diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c index f910dfccbf5d..69f7043a98b9 100644 --- a/arch/riscv/kernel/traps.c +++ b/arch/riscv/kernel/traps.c @@ -18,6 +18,7 @@ #include <linux/irq.h> #include <linux/kexec.h> #include <linux/entry-common.h> +#include <linux/context_tracking.h> #include <asm/asm-prototypes.h> #include <asm/bug.h> @@ -285,12 +286,18 @@ asmlinkage __visible __trap_section void do_trap_break(struct pt_regs *regs) handle_break(regs); irqentry_exit_to_user_mode(regs); - } else { + } else if (in_interrupt()){ irqentry_state_t state = irqentry_nmi_enter(regs); handle_break(regs); irqentry_nmi_exit(regs, state); + } else { + enum ctx_state prev_state = exception_enter(); + + handle_break(regs); + + exception_exit(prev_state); } } > > If that makes kdb unhappy, fix kdb. > > > Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry") > > Reported-by: Daniel Thompson <daniel.thompson@linaro.org> > > Signed-off-by: Guo Ren <guoren@linux.alibaba.com> > > Signed-off-by: Guo Ren <guoren@kernel.org> > > Cc: stable@vger.kernel.org > > --- > > arch/riscv/kernel/traps.c | 5 +++-- > > 1 file changed, 3 insertions(+), 2 deletions(-) > > > > diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c > > index efc6b649985a..ed0eb9452f9e 100644 > > --- a/arch/riscv/kernel/traps.c > > +++ b/arch/riscv/kernel/traps.c > > @@ -18,6 +18,7 @@ > > #include <linux/irq.h> > > #include <linux/kexec.h> > > #include <linux/entry-common.h> > > +#include <linux/context_tracking.h> > > > > #include <asm/asm-prototypes.h> > > #include <asm/bug.h> > > @@ -257,11 +258,11 @@ asmlinkage __visible __trap_section void do_trap_break(struct pt_regs *regs) > > > > irqentry_exit_to_user_mode(regs); > > } else { > > - irqentry_state_t state = irqentry_nmi_enter(regs); > > + enum ctx_state prev_state = exception_enter(); > > > > handle_break(regs); > > > > - irqentry_nmi_exit(regs, state); > > + exception_exit(prev_state); > > } > > } > > > > -- > > 2.36.1 > > -- Best Regards Guo Ren
On Sun, Jul 09, 2023 at 10:30:22AM +0800, Guo Ren wrote: > On Wed, Jul 5, 2023 at 12:40 AM Peter Zijlstra <peterz@infradead.org> wrote: > > > > On Sat, Jul 01, 2023 at 10:57:07PM -0400, guoren@kernel.org wrote: > > > From: Guo Ren <guoren@linux.alibaba.com> > > > > > > The irqentry_nmi_enter/exit would force the current context into in_interrupt. > > > That would trigger the kernel to dead panic, but the kdb still needs "ebreak" to > > > debug the kernel. > > > > > > Move irqentry_nmi_enter/exit to exception_enter/exit could correct handle_break > > > of the kernel side. > > > > This doesn't explain much if anything :/ > > > > I'm confused (probably because I don't know RISC-V very well), what's > > EBREAK and how does it happen? > EBREAK is just an instruction of riscv which would rise breakpoint exception. > > > > > > Specifically, if EBREAK can happen inside an local_irq_disable() region, > > then the below change is actively wrong. Any exception/interrupt that > > can happen while local_irq_disable() must be treated like an NMI. > When the ebreak happend out of local_irq_disable region, but > __nmi_enter forces handle_break() into in_interupt() state. So how And why is that a problem? I think I'm missing something fundamental here... > about: > > diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c > index f910dfccbf5d..69f7043a98b9 100644 > --- a/arch/riscv/kernel/traps.c > +++ b/arch/riscv/kernel/traps.c > @@ -18,6 +18,7 @@ > #include <linux/irq.h> > #include <linux/kexec.h> > #include <linux/entry-common.h> > +#include <linux/context_tracking.h> > > #include <asm/asm-prototypes.h> > #include <asm/bug.h> > @@ -285,12 +286,18 @@ asmlinkage __visible __trap_section void > do_trap_break(struct pt_regs *regs) > handle_break(regs); > > irqentry_exit_to_user_mode(regs); > - } else { > + } else if (in_interrupt()){ > irqentry_state_t state = irqentry_nmi_enter(regs); > > handle_break(regs); > > irqentry_nmi_exit(regs, state); > + } else { > + enum ctx_state prev_state = exception_enter(); > + > + handle_break(regs); > + > + exception_exit(prev_state); > } > } That's wrong. If you want to make it conditional, you have to look at !(regs->status & SR_IE) (that's the interrupt enable flag of the interrupted context, right?) When you hit an EBREAK when IRQs were disabled, you must be NMI like. But making it conditional like this makes it really hard to write a handler though, it basically must assume it will be NMI contetx (because it can't know) so there is no point in sometimes not doing NMI context.
On Mon, Jul 10, 2023 at 4:02 PM Peter Zijlstra <peterz@infradead.org> wrote: > > On Sun, Jul 09, 2023 at 10:30:22AM +0800, Guo Ren wrote: > > On Wed, Jul 5, 2023 at 12:40 AM Peter Zijlstra <peterz@infradead.org> wrote: > > > > > > On Sat, Jul 01, 2023 at 10:57:07PM -0400, guoren@kernel.org wrote: > > > > From: Guo Ren <guoren@linux.alibaba.com> > > > > > > > > The irqentry_nmi_enter/exit would force the current context into in_interrupt. > > > > That would trigger the kernel to dead panic, but the kdb still needs "ebreak" to > > > > debug the kernel. > > > > > > > > Move irqentry_nmi_enter/exit to exception_enter/exit could correct handle_break > > > > of the kernel side. > > > > > > This doesn't explain much if anything :/ > > > > > > I'm confused (probably because I don't know RISC-V very well), what's > > > EBREAK and how does it happen? > > EBREAK is just an instruction of riscv which would rise breakpoint exception. > > > > > > > > > > Specifically, if EBREAK can happen inside an local_irq_disable() region, > > > then the below change is actively wrong. Any exception/interrupt that > > > can happen while local_irq_disable() must be treated like an NMI. > > When the ebreak happend out of local_irq_disable region, but > > __nmi_enter forces handle_break() into in_interupt() state. So how > > And why is that a problem? I think I'm missing something fundamental > here... The irqentry_nmi_enter() would force the current context to get in_interrupt=true, although ebreak happens in the context which is in_interrupt=false. A lot of checking codes, such as: if (in_interrupt()) panic("Fatal exception in interrupt"); It would make the kernel panic, but we don't panic; we want back to the shell. eg: echo BUG > /sys/kernel/debug/provoke-crash/DIRECT > > > about: > > > > diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c > > index f910dfccbf5d..69f7043a98b9 100644 > > --- a/arch/riscv/kernel/traps.c > > +++ b/arch/riscv/kernel/traps.c > > @@ -18,6 +18,7 @@ > > #include <linux/irq.h> > > #include <linux/kexec.h> > > #include <linux/entry-common.h> > > +#include <linux/context_tracking.h> > > > > #include <asm/asm-prototypes.h> > > #include <asm/bug.h> > > @@ -285,12 +286,18 @@ asmlinkage __visible __trap_section void > > do_trap_break(struct pt_regs *regs) > > handle_break(regs); > > > > irqentry_exit_to_user_mode(regs); > > - } else { > > + } else if (in_interrupt()){ > > irqentry_state_t state = irqentry_nmi_enter(regs); > > > > handle_break(regs); > > > > irqentry_nmi_exit(regs, state); > > + } else { > > + enum ctx_state prev_state = exception_enter(); > > + > > + handle_break(regs); > > + > > + exception_exit(prev_state); > > } > > } > > That's wrong. If you want to make it conditional, you have to look at > !(regs->status & SR_IE) (that's the interrupt enable flag of the > interrupted context, right?) > > When you hit an EBREAK when IRQs were disabled, you must be NMI like. > > But making it conditional like this makes it really hard to write a > handler though, it basically must assume it will be NMI contetx (because > it can't know) so there is no point in sometimes not doing NMI context.
On Mon, Jul 17, 2023 at 07:33:25AM +0800, Guo Ren wrote: > On Mon, Jul 10, 2023 at 4:02 PM Peter Zijlstra <peterz@infradead.org> wrote: > > > > On Sun, Jul 09, 2023 at 10:30:22AM +0800, Guo Ren wrote: > > > On Wed, Jul 5, 2023 at 12:40 AM Peter Zijlstra <peterz@infradead.org> wrote: > > > > > > > > On Sat, Jul 01, 2023 at 10:57:07PM -0400, guoren@kernel.org wrote: > > > > > From: Guo Ren <guoren@linux.alibaba.com> > > > > > > > > > > The irqentry_nmi_enter/exit would force the current context into in_interrupt. > > > > > That would trigger the kernel to dead panic, but the kdb still needs "ebreak" to > > > > > debug the kernel. > > > > > > > > > > Move irqentry_nmi_enter/exit to exception_enter/exit could correct handle_break > > > > > of the kernel side. > > > > > > > > This doesn't explain much if anything :/ > > > > > > > > I'm confused (probably because I don't know RISC-V very well), what's > > > > EBREAK and how does it happen? > > > EBREAK is just an instruction of riscv which would rise breakpoint exception. > > > > > > > > > > > > > > Specifically, if EBREAK can happen inside an local_irq_disable() region, > > > > then the below change is actively wrong. Any exception/interrupt that > > > > can happen while local_irq_disable() must be treated like an NMI. > > > When the ebreak happend out of local_irq_disable region, but > > > __nmi_enter forces handle_break() into in_interupt() state. So how > > > > And why is that a problem? I think I'm missing something fundamental > > here... > The irqentry_nmi_enter() would force the current context to get > in_interrupt=true, although ebreak happens in the context which is > in_interrupt=false. > A lot of checking codes, such as: > if (in_interrupt()) > panic("Fatal exception in interrupt"); Why would you do that?!? Are you're trying to differentiate between an exception and an interrupt? You *could* have ebreak in an interrupt, right? So why panic the machine if that happens? > It would make the kernel panic, but we don't panic; we want back to the shell. > eg: > echo BUG > /sys/kernel/debug/provoke-crash/DIRECT
On Mon, Jul 17, 2023 at 6:45 PM Peter Zijlstra <peterz@infradead.org> wrote: > > On Mon, Jul 17, 2023 at 07:33:25AM +0800, Guo Ren wrote: > > On Mon, Jul 10, 2023 at 4:02 PM Peter Zijlstra <peterz@infradead.org> wrote: > > > > > > On Sun, Jul 09, 2023 at 10:30:22AM +0800, Guo Ren wrote: > > > > On Wed, Jul 5, 2023 at 12:40 AM Peter Zijlstra <peterz@infradead.org> wrote: > > > > > > > > > > On Sat, Jul 01, 2023 at 10:57:07PM -0400, guoren@kernel.org wrote: > > > > > > From: Guo Ren <guoren@linux.alibaba.com> > > > > > > > > > > > > The irqentry_nmi_enter/exit would force the current context into in_interrupt. > > > > > > That would trigger the kernel to dead panic, but the kdb still needs "ebreak" to > > > > > > debug the kernel. > > > > > > > > > > > > Move irqentry_nmi_enter/exit to exception_enter/exit could correct handle_break > > > > > > of the kernel side. > > > > > > > > > > This doesn't explain much if anything :/ > > > > > > > > > > I'm confused (probably because I don't know RISC-V very well), what's > > > > > EBREAK and how does it happen? > > > > EBREAK is just an instruction of riscv which would rise breakpoint exception. > > > > > > > > > > > > > > > > > > Specifically, if EBREAK can happen inside an local_irq_disable() region, > > > > > then the below change is actively wrong. Any exception/interrupt that > > > > > can happen while local_irq_disable() must be treated like an NMI. > > > > When the ebreak happend out of local_irq_disable region, but > > > > __nmi_enter forces handle_break() into in_interupt() state. So how > > > > > > And why is that a problem? I think I'm missing something fundamental > > > here... > > The irqentry_nmi_enter() would force the current context to get > > in_interrupt=true, although ebreak happens in the context which is > > in_interrupt=false. > > A lot of checking codes, such as: > > if (in_interrupt()) > > panic("Fatal exception in interrupt"); > > Why would you do that?!? > > Are you're trying to differentiate between an exception and an > interrupt? > > You *could* have ebreak in an interrupt, right? So why panic the machine > if that happens? Do you mean the below patch? Yes, it could fix up. diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c index f910dfccbf5d..92899db6696b 100644 --- a/arch/riscv/kernel/traps.c +++ b/arch/riscv/kernel/traps.c @@ -85,8 +85,6 @@ void die(struct pt_regs *regs, const char *str) spin_unlock_irqrestore(&die_lock, flags); oops_exit(); - if (in_interrupt()) - panic("Fatal exception in interrupt"); if (panic_on_oops) panic("Fatal exception"); if (ret != NOTIFY_STOP) diff --git a/kernel/exit.c b/kernel/exit.c index edb50b4c9972..a46a1aef66ce 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -940,8 +940,6 @@ void __noreturn make_task_dead(int signr) struct task_struct *tsk = current; unsigned int limit; - if (unlikely(in_interrupt())) - panic("Aiee, killing interrupt handler!"); if (unlikely(!tsk->pid)) panic("Attempted to kill the idle task!"); But how does x86 deal with it without kernel/exit.c modifcation? > > > It would make the kernel panic, but we don't panic; we want back to the shell. > > eg: > > echo BUG > /sys/kernel/debug/provoke-crash/DIRECT > > >
diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c index efc6b649985a..ed0eb9452f9e 100644 --- a/arch/riscv/kernel/traps.c +++ b/arch/riscv/kernel/traps.c @@ -18,6 +18,7 @@ #include <linux/irq.h> #include <linux/kexec.h> #include <linux/entry-common.h> +#include <linux/context_tracking.h> #include <asm/asm-prototypes.h> #include <asm/bug.h> @@ -257,11 +258,11 @@ asmlinkage __visible __trap_section void do_trap_break(struct pt_regs *regs) irqentry_exit_to_user_mode(regs); } else { - irqentry_state_t state = irqentry_nmi_enter(regs); + enum ctx_state prev_state = exception_enter(); handle_break(regs); - irqentry_nmi_exit(regs, state); + exception_exit(prev_state); } }