On Wed, Apr 24, 2019 at 3:47 AM He Zhe <zhe...@windriver.com> wrote:
> This is for standard/base and all sub-level branches. For explanation, see
> the
> bottom of the commit log I append.
>
Which kernel versions ? I didn't notice a version it the shortlog or
temporary section, but I may have overlooked it.
Bruce
>
> Zhe
>
> On 4/24/19 3:42 PM, zhe...@windriver.com wrote:
> > From: "Steven Rostedt (VMware)" <rost...@goodmis.org>
> >
> > He Zhe reported a crash by enabling trace events and selecting
> > "userstacktrace" which will read the stack of userspace for every trace
> > event recorded. Zhe narrowed it down to:
> >
> > c3bc8fd637a9 ("tracing: Centralize preemptirq tracepoints and unify
> their usage")
> >
> > With the problem config, I was able to also reproduce the error. I
> > narrowed it down to just having to do the following:
> >
> > # cd /sys/kernel/tracing
> > # echo 1 > options/userstacktrace
> > # echo 1 > events/preemptirq/irq_disable/enable
> >
> > And sure enough, I triggered a crash. Well, it was systemd crashing
> > with a bad memory access??
> >
> > systemd-journal[537]: segfault at ed8cb8 ip 00007f7fffc9fef5 sp
> 00007ffc4062cb10 error 7
> >
> > And it would crash similarly each time I tried it, but always at a
> > different place. After spending the day on this, I finally figured it
> > out. The bug is happening in entry_64.S right after error_entry.
> > There's two TRACE_IRQS_OFF in that code path, which if I comment out,
> > the bug goes away. Then it dawned on me that the crash always happens
> > when systemd does a normal page fault. We had this bug before, and it
> > was with the exception trace points.
> >
> > The issue is that a tracepoint can fault (reading vmalloc or whatever).
> > And doing a userspace stack trace most definitely will fault. But if we
> > are coming from a legitimate page fault, the address of that fault (in
> > the CR2 register) will be lost if we fault before we get to the page
> > fault handler. That's exactly what is happening.
> >
> > To solve this, a TRACE_IRQS_OFF_CR2 (and ON for consistency) was added
> > that saves the CR2 register. A new trace_hardirqs_off_thunk_cr2 is
> > created that stores the cr2 register, calls the
> > trace_hardirqs_off_caller, then on return restores the cr2 register if
> > it changed, before returning.
> >
> > On my tests this fixes the issue. I just want to know if this is a
> > legitimate fix or if someone can come up with a better fix?
> >
> > Note: this also saves the exception context just like the
> > do_page_fault() function does.
> >
> > Note2: This only gets enabled when lockdep or irq tracing is enabled,
> > which is not recommended for production environments.
> >
> > Link:
> http://lkml.kernel.org/r/897cf5cf-fc24-8a64-cb28-847f2d2e6...@windriver.com
> >
> > Fixes: c3bc8fd637a9 ("tracing: Centralize preemptirq tracepoints and
> unify their usage")
> > Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org>
> >
> > Link:
> https://lore.kernel.org/lkml/20190320221534.165ab...@oasis.local.home/
> >
> > This might not be the final solution. But the upstream thread has
> stopped over
> > a month and there is unlikely a final solution in the near future.
> >
> > Since the diff looks quite clear and does not affect other functions. It
> should
> > be worth adding this initial patch from the maintainer.
> >
> > Signed-off-by: He Zhe <zhe...@windriver.com>
> > ---
> > arch/x86/entry/common.c | 26 ++++++++++++++++++++++++++
> > arch/x86/entry/entry_64.S | 4 ++--
> > arch/x86/entry/thunk_64.S | 2 ++
> > arch/x86/include/asm/irqflags.h | 4 ++++
> > 4 files changed, 34 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
> > index 7bc105f..7edffec 100644
> > --- a/arch/x86/entry/common.c
> > +++ b/arch/x86/entry/common.c
> > @@ -292,6 +292,32 @@ __visible void do_syscall_64(unsigned long nr,
> struct pt_regs *regs)
> >
> > syscall_return_slowpath(regs);
> > }
> > +
> > +extern void trace_hardirqs_on_caller(unsigned long caller_addr);
> > +__visible void trace_hardirqs_on_caller_cr2(unsigned long caller_addr)
> > +{
> > + unsigned long address = read_cr2(); /* Get the faulting address */
> > + enum ctx_state prev_state;
> > +
> > + prev_state = exception_enter();
> > + trace_hardirqs_on_caller(caller_addr);
> > + if (address != read_cr2())
> > + write_cr2(address);
> > + exception_exit(prev_state);
> > +}
> > +
> > +extern void trace_hardirqs_off_caller(unsigned long caller_addr);
> > +__visible void trace_hardirqs_off_caller_cr2(unsigned long caller_addr)
> > +{
> > + unsigned long address = read_cr2(); /* Get the faulting address */
> > + enum ctx_state prev_state;
> > +
> > + prev_state = exception_enter();
> > + trace_hardirqs_off_caller(caller_addr);
> > + if (address != read_cr2())
> > + write_cr2(address);
> > + exception_exit(prev_state);
> > +}
> > #endif
> >
> > #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
> > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> > index 1f0efdb..73ddf24 100644
> > --- a/arch/x86/entry/entry_64.S
> > +++ b/arch/x86/entry/entry_64.S
> > @@ -1248,12 +1248,12 @@ ENTRY(error_entry)
> > * we fix gsbase, and we should do it before enter_from_user_mode
> > * (which can take locks).
> > */
> > - TRACE_IRQS_OFF
> > + TRACE_IRQS_OFF_CR2
> > CALL_enter_from_user_mode
> > ret
> >
> > .Lerror_entry_done:
> > - TRACE_IRQS_OFF
> > + TRACE_IRQS_OFF_CR2
> > ret
> >
> > /*
> > diff --git a/arch/x86/entry/thunk_64.S b/arch/x86/entry/thunk_64.S
> > index be36bf4..1300b53 100644
> > --- a/arch/x86/entry/thunk_64.S
> > +++ b/arch/x86/entry/thunk_64.S
> > @@ -41,6 +41,8 @@
> > #ifdef CONFIG_TRACE_IRQFLAGS
> > THUNK trace_hardirqs_on_thunk,trace_hardirqs_on_caller,1
> > THUNK trace_hardirqs_off_thunk,trace_hardirqs_off_caller,1
> > + THUNK trace_hardirqs_on_thunk_cr2,trace_hardirqs_on_caller_cr2,1
> > + THUNK trace_hardirqs_off_thunk_cr2,trace_hardirqs_off_caller_cr2,1
> > #endif
> >
> > #ifdef CONFIG_DEBUG_LOCK_ALLOC
> > diff --git a/arch/x86/include/asm/irqflags.h
> b/arch/x86/include/asm/irqflags.h
> > index 058e40f..dd51174 100644
> > --- a/arch/x86/include/asm/irqflags.h
> > +++ b/arch/x86/include/asm/irqflags.h
> > @@ -172,9 +172,13 @@ static inline int arch_irqs_disabled(void)
> > #ifdef CONFIG_TRACE_IRQFLAGS
> > # define TRACE_IRQS_ON call trace_hardirqs_on_thunk;
> > # define TRACE_IRQS_OFF call trace_hardirqs_off_thunk;
> > +# define TRACE_IRQS_ON_CR2 call trace_hardirqs_on_thunk_cr2;
> > +# define TRACE_IRQS_OFF_CR2 call trace_hardirqs_off_thunk_cr2;
> > #else
> > # define TRACE_IRQS_ON
> > # define TRACE_IRQS_OFF
> > +# define TRACE_IRQS_ON_CR2
> > +# define TRACE_IRQS_OFF_CR2
> > #endif
> > #ifdef CONFIG_DEBUG_LOCK_ALLOC
> > # ifdef CONFIG_X86_64
>
>
--
- Thou shalt not follow the NULL pointer, for chaos and madness await thee
at its end
- "Use the force Harry" - Gandalf, Star Trek II
--
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