From: Guo Ren <[email protected]>
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.
Before the fixup:
$echo BUG > /sys/kernel/debug/provoke-crash/DIRECT
lkdtm: Performing direct entry BUG
------------[ cut here ]------------
kernel BUG at drivers/misc/lkdtm/bugs.c:78!
handle_break, 256.
Kernel BUG [#1]
Modules linked in:
CPU: 0 PID: 104 Comm: echo Not tainted 6.4.0-rc1-00055-g0ca05a4b079f-dirty #30
Hardware name: riscv-virtio,qemu (DT)
epc : lkdtm_BUG+0x6/0x8
ra : lkdtm_do_action+0x14/0x1c
epc : ffffffff8055c730 ra : ffffffff8087e188 sp : ff200000007dbd40
gp : ffffffff81500878 tp : ff600000028ebac0 t0 : 6500000000000000
t1 : 000000000000006c t2 : 6550203a6d74646b s0 : ff200000007dbd50
s1 : ffffffff814bfc80 a0 : ffffffff814bfc80 a1 : ff6000001ffd8608
a2 : ff6000001ffdb870 a3 : 0000000000000000 a4 : 0000000000000000
a5 : ffffffff8055c72a a6 : 0000000000000032 a7 : 0000000000000038
s2 : 0000000000000004 s3 : 00000000556371a0 s4 : ff200000007dbe70
s5 : ff60000002090000 s6 : 00000000556371a0 s7 : 0000000000000030
s8 : 000000007fffec78 s9 : 0000000000000007 s10: 0000000055637530
s11: 0000000000000001 t3 : ffffffff81513ed7 t4 : ffffffff81513ed7
t5 : ffffffff81513ed8 t6 : ff200000007dbb88
status: 0000000100000120 badaddr: 0000000000000000 cause: 0000000000000003
[<ffffffff8055c730>] lkdtm_BUG+0x6/0x8
Code: 0513 6b05 b097 0031 80e7 e960 b705 1141 e422 0800 (9002) 1141
---[ end trace 0000000000000000 ]---
Kernel panic - not syncing: Aiee, killing interrupt handler!
---[ end Kernel panic - not syncing: Aiee, killing interrupt handler! ]---
(Dead in the kernel side.)
After the fixup:
$echo BUG > /sys/kernel/debug/provoke-crash/DIRECT
lkdtm: Performing direct entry BUG
------------[ cut here ]------------
kernel BUG at drivers/misc/lkdtm/bugs.c:78!
Kernel BUG [#13]
Modules linked in:
CPU: 0 PID: 129 Comm: echo Tainted: G D 6.4.0-rc1-00055-g0ca05a4b079f-dirty #34
Hardware name: riscv-virtio,qemu (DT)
epc : lkdtm_BUG+0x6/0x8
ra : lkdtm_do_action+0x14/0x1c
epc : ffffffff8055c71c ra : ffffffff8087e170 sp : ff200000007e3d40
gp : ffffffff81500878 tp : ff600000028ebac0 t0 : 6500000000000000
t1 : 000000000000006c t2 : 6550203a6d74646b s0 : ff200000007e3d50
s1 : ffffffff814bfc80 a0 : ffffffff814bfc80 a1 : ff6000001ffd8608
a2 : ff6000001ffdb870 a3 : 0000000000000000 a4 : 0000000000000000
a5 : ffffffff8055c716 a6 : 0000000000000032 a7 : 0000000000000038
s2 : 0000000000000004 s3 : 00000000556371a0 s4 : ff200000007e3e70
s5 : ff60000002090000 s6 : 00000000556371a0 s7 : 0000000000000030
s8 : 000000007fffec78 s9 : 0000000000000007 s10: 0000000055637530
s11: 0000000000000001 t3 : ffffffff81513ed7 t4 : ffffffff81513ed7
t5 : ffffffff81513ed8 t6 : ff200000007e3b88
status: 0000000100000120 badaddr: 0000000000000000 cause: 0000000000000003
[<ffffffff8055c71c>] lkdtm_BUG+0x6/0x8
Code: 0513 6945 b097 0031 80e7 e920 b705 1141 e422 0800 (9002) 1141
---[ end trace 0000000000000000 ]---
note: echo[129] exited with irqs disabled
Segmentation fault
(Resume to the shell normally.)
Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry")
Reported-by: Daniel Thompson <[email protected]>
Signed-off-by: Guo Ren <[email protected]>
Signed-off-by: Guo Ren <[email protected]>
Cc: [email protected]
---
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 Sat, Jul 01, 2023 at 10:57:07PM -0400, [email protected] wrote:
> From: Guo Ren <[email protected]>
>
> 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 <[email protected]>
> Signed-off-by: Guo Ren <[email protected]>
> Signed-off-by: Guo Ren <[email protected]>
> Cc: [email protected]
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 <[email protected]>
Daniel.
On Mon, Jul 3, 2023 at 6:29 PM Daniel Thompson
<[email protected]> wrote:
>
> On Sat, Jul 01, 2023 at 10:57:07PM -0400, [email protected] wrote:
> > From: Guo Ren <[email protected]>
> >
> > 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 <[email protected]>
> > Signed-off-by: Guo Ren <[email protected]>
> > Signed-off-by: Guo Ren <[email protected]>
> > Cc: [email protected]
>
> 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 <[email protected]>
Thx for the report & tested-by.
>
>
> Daniel.
--
Best Regards
Guo Ren
On Sat, Jul 01, 2023 at 10:57:07PM -0400, [email protected] wrote:
> From: Guo Ren <[email protected]>
>
> 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 <[email protected]>
> Signed-off-by: Guo Ren <[email protected]>
> Signed-off-by: Guo Ren <[email protected]>
> Cc: [email protected]
> ---
> 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, [email protected] wrote:
> > From: Guo Ren <[email protected]>
> >
> > 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 <[email protected]> wrote:
>
> On Sat, Jul 01, 2023 at 10:57:07PM -0400, [email protected] wrote:
> > From: Guo Ren <[email protected]>
> >
> > 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 <[email protected]>
> > Signed-off-by: Guo Ren <[email protected]>
> > Signed-off-by: Guo Ren <[email protected]>
> > Cc: [email protected]
> > ---
> > 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 <[email protected]> wrote:
> >
> > On Sat, Jul 01, 2023 at 10:57:07PM -0400, [email protected] wrote:
> > > From: Guo Ren <[email protected]>
> > >
> > > 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 <[email protected]> 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 <[email protected]> wrote:
> > >
> > > On Sat, Jul 01, 2023 at 10:57:07PM -0400, [email protected] wrote:
> > > > From: Guo Ren <[email protected]>
> > > >
> > > > 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.
--
Best Regards
Guo Ren
On Mon, Jul 17, 2023 at 07:33:25AM +0800, Guo Ren wrote:
> On Mon, Jul 10, 2023 at 4:02 PM Peter Zijlstra <[email protected]> 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 <[email protected]> wrote:
> > > >
> > > > On Sat, Jul 01, 2023 at 10:57:07PM -0400, [email protected] wrote:
> > > > > From: Guo Ren <[email protected]>
> > > > >
> > > > > 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 <[email protected]> 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 <[email protected]> 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 <[email protected]> wrote:
> > > > >
> > > > > On Sat, Jul 01, 2023 at 10:57:07PM -0400, [email protected] wrote:
> > > > > > From: Guo Ren <[email protected]>
> > > > > >
> > > > > > 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
>
>
>
--
Best Regards
Guo Ren