Messages in this thread | | | Date | Wed, 2 Dec 2015 12:36:55 +0000 | From | Will Deacon <> | Subject | Re: [PATCH] arm64: ftrace: stop using kstop_machine to enable/disable tracing |
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On Sat, Nov 28, 2015 at 03:50:09PM +0800, Li Bin wrote: > On arm64, kstop_machine which is hugely disruptive to a running > system is not needed to convert nops to ftrace calls or back, > because that modifed code is a single 32bit instructions which > is impossible to cross cache (or page) boundaries, and the used str > instruction is single-copy atomic.
This commit message is misleading, since the single-copy atomicity guarantees don't apply to the instruction-side. Instead, the architecture calls out a handful of safe instructions in "Concurrent modification and execution of instructions".
Now, those safe instructions *do* include NOP, B and BL, so that should be sufficient for ftrace provided that we don't patch condition codes (and I don't think we do).
> Cc: <stable@vger.kernel.org> # 3.18+
I don't think this is stable material.
Will
> Signed-off-by: Li Bin <huawei.libin@huawei.com> > --- > arch/arm64/kernel/ftrace.c | 5 +++++ > 1 files changed, 5 insertions(+), 0 deletions(-) > > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c > index c851be7..9669b33 100644 > --- a/arch/arm64/kernel/ftrace.c > +++ b/arch/arm64/kernel/ftrace.c > @@ -93,6 +93,11 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, > return ftrace_modify_code(pc, old, new, true); > } > > +void arch_ftrace_update_code(int command) > +{ > + ftrace_modify_all_code(command); > +} > + > int __init ftrace_dyn_arch_init(void) > { > return 0; > -- > 1.7.1 >
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