ACK/Cmnt + APPLIED[?]: [HIRSUTE][linux-riscv][PATCH v2] UBUNTU: SAUCE: RISC-V: prevent sbi_send_cpumask_ipi race with ftrace

[Dimitri John Ledkov]

On Thu, Aug 12, 2021 at 9:47 AM Stefan Bader <stefan.bader at canonical.com> wrote:
>
> On 11.08.21 11:23, Dimitri John Ledkov wrote:
> > From: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
> >
> > ftrace will patch instructions in sbi_send_cpumask_ipi, which is going to
> > be used by flush_icache_range, leading to potential races and crashes like
> > this:
> >
> > [    0.000000] ftrace: allocating 38893 entries in 152 pages
> > [    0.000000] Oops - illegal instruction [#1]
> > [    0.000000] Modules linked in:
> > [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.11.0-1014-generic #14-Ubuntu
> > [    0.000000] epc: ffffffe00000920e ra : ffffffe000009384 sp : ffffffe001803d30
> > [    0.000000]  gp : ffffffe001a14240 tp : ffffffe00180f440 t0 : ffffffe07fe38000
> > [    0.000000]  t1 : ffffffe0019cd338 t2 : 0000000000000000 s0 : ffffffe001803d70
> > [    0.000000]  s1 : 0000000000000000 a0 : ffffffe0000095aa a1 : 0000000000000001
> > [    0.000000]  a2 : 0000000000000002 a3 : 0000000000000000 a4 : 0000000000000000
> > [    0.000000]  a5 : 0000000000000000 a6 : 0000000000000004 a7 : 0000000052464e43
> > [    0.000000]  s2 : 0000000000000002 s3 : 0000000000000001 s4 : 0000000000000000
> > [    0.000000]  s5 : 0000000000000000 s6 : 0000000000000000 s7 : 0000000000000000
> > [    0.000000]  s8 : ffffffe001a170c0 s9 : 0000000000000001 s10: 0000000000000001
> > [    0.000000]  s11: 00000000fffcc5d0 t3 : 0000000000000068 t4 : 000000000000000b
> > [    0.000000]  t5 : ffffffe0019cd3e0 t6 : ffffffe001803cd8
> > [    0.000000] status: 0000000200000100 badaddr: 000000000513f187 cause: 0000000000000002
> > [    0.000000] ---[ end trace f67eb9af4d8d492b ]---
> > [    0.000000] Kernel panic - not syncing: Attempted to kill the idle task!
> > [    0.000000] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---
> >
> > Where ffffffe00000920e lies in the middle of sbi_send_cpumask_ipi.
> >
> > BugLink: https://bugs.launchpad.net/bugs/1934548
> > Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
> > Tested-by: Dimitri John Ledkov <dimitri.ledkov at canonical.com>
> > Signed-off-by: Dimitri John Ledkov <dimitri.ledkov at canonical.com>
> > ---
> >
> >   Patch can be applied to:
> >   - Unstable
> >   - Impish linux
> >   - Impish linux-riscv
> >   - Hirsute linux
> >   - Hirsute linux-riscv
> >   - Focal linux-riscv-5.11
> >
> >   Whichever are suitable for respins.
> >
> >   Changes since v1:
> >   - Added BugLink, Tested-By, SOB
> >
> >   arch/riscv/kernel/sbi.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
> > index b8f82c73de..9f85f0656f 100644
> > --- a/arch/riscv/kernel/sbi.c
> > +++ b/arch/riscv/kernel/sbi.c
> > @@ -562,7 +562,7 @@ long sbi_get_impid(void)
> >       return __sbi_base_ecall(SBI_EXT_BASE_GET_MIMPID);
> >   }
> >
> > -static void sbi_send_cpumask_ipi(const struct cpumask *target)
> > +static void notrace sbi_send_cpumask_ipi(const struct cpumask *target)
> >   {
> >       struct cpumask hartid_mask;
> >
> >
>
> The related bug shows this as applied already without second ACK and not even
> sending the APPLIED email. Whoever did this should refresh memory about process.
> Anyhow:
>
> Acked-by: Stefan Bader <stefan.bader at canonical.com>
>

It is applied into hirsute:linux-riscv (and also
hirsute:linux-riscv-5.11). But still need to apply into
impish:unstable & impish:linux-riscv. Maybe just "impish:linux".

re:second Ack - cascardo is the author, I reviewed & tested the patch
and also posted it to the mailing list, and got acked by Tim. In my
mind the two Acks were from myself and Tim. Should I have sent an ACK
to the mailing too? Or should I have asked cycle lead klebs to send an
Ack when we agreed to add respin for the said kernels?

-- 
Regards,

Dimitri.