On Wed, 24 Feb 2021 at 23:39, Doug Anderson <diand...@chromium.org> wrote:
>
> Hi,
>
> On Wed, Feb 24, 2021 at 12:17 AM Sumit Garg <sumit.g...@linaro.org> wrote:
> >
> > Currently breakpoints in kernel .init.text section are not handled
> > correctly while allowing to remove them even after corresponding pages
> > have been freed.
> >
> > Fix it via killing .init.text section breakpoints just prior to initmem
> > pages being freed.
>
> It might be worth it to mention that HW breakpoints aren't handled by
> this patch but it's probably not such a big deal.
>
>
> > Suggested-by: Doug Anderson <diand...@chromium.org>
> > Signed-off-by: Sumit Garg <sumit.g...@linaro.org>
> > ---
> > include/linux/kgdb.h | 2 ++
> > init/main.c | 1 +
> > kernel/debug/debug_core.c | 11 +++++++++++
> > 3 files changed, 14 insertions(+)
> >
> > diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
> > index 57b8885708e5..3aa503ef06fc 100644
> > --- a/include/linux/kgdb.h
> > +++ b/include/linux/kgdb.h
> > @@ -361,9 +361,11 @@ extern atomic_t kgdb_active;
> > extern bool dbg_is_early;
> > extern void __init dbg_late_init(void);
> > extern void kgdb_panic(const char *msg);
> > +extern void kgdb_free_init_mem(void);
> > #else /* ! CONFIG_KGDB */
> > #define in_dbg_master() (0)
> > #define dbg_late_init()
> > static inline void kgdb_panic(const char *msg) {}
> > +static inline void kgdb_free_init_mem(void) { }
> > #endif /* ! CONFIG_KGDB */
> > #endif /* _KGDB_H_ */
> > diff --git a/init/main.c b/init/main.c
> > index c68d784376ca..a446ca3d334e 100644
> > --- a/init/main.c
> > +++ b/init/main.c
> > @@ -1417,6 +1417,7 @@ static int __ref kernel_init(void *unused)
> > async_synchronize_full();
> > kprobe_free_init_mem();
> > ftrace_free_init_mem();
> > + kgdb_free_init_mem();
> > free_initmem();
> > mark_readonly();
> >
> > diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
> > index 229dd119f430..319381e95d1d 100644
> > --- a/kernel/debug/debug_core.c
> > +++ b/kernel/debug/debug_core.c
> > @@ -465,6 +465,17 @@ int dbg_remove_all_break(void)
> > return 0;
> > }
> >
> > +void kgdb_free_init_mem(void)
> > +{
> > + int i;
> > +
> > + /* Clear init memory breakpoints. */
> > + for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
> > + if (init_section_contains((void *)kgdb_break[i].bpt_addr,
> > 0))
>
> A nit, but instead of 0 should this be passing "BREAK_INSTR_SIZE" ?
>
> Also: even if memory is about to get freed it still seems like it'd be
> wise to call this:
>
> kgdb_arch_remove_breakpoint(&kgdb_break[i]);
>
> It looks like it shouldn't matter today but just in case an
> architecture decides to do something fancy in the future it might not
> hurt to tell it that the breakpoint is going away.
>
>
> Everything here is pretty nitty, though. This looks good to me now.
>
> Reviewed-by: Douglas Anderson <diand...@chromium.org>
Thanks Doug for your review.
-Sumit
