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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Feb 01, 2023 at 05:34:16PM +0100, Florent Revest wrote: > All direct calls are now registered using the register_ftrace_direct API > so each ops can jump to only one direct-called trampoline. > > By storing the direct called trampoline address directly in the ops we > can save one hashmap lookup in the direct call ops and implement arm64 > direct calls on top of call ops. > > Signed-off-by: Florent Revest > --- > include/linux/ftrace.h | 3 +++ > kernel/trace/ftrace.c | 6 ++++-- > 2 files changed, 7 insertions(+), 2 deletions(-) > > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h > index a7dbd307c3a4..84f717f8959e 100644 > --- a/include/linux/ftrace.h > +++ b/include/linux/ftrace.h > @@ -321,6 +321,9 @@ struct ftrace_ops { > unsigned long trampoline_size; > struct list_head list; > ftrace_ops_func_t ops_func; > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS > + unsigned long direct_call; > +#endif > #endif > }; > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index cb77a0a208c7..b0426de11c45 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -2577,9 +2577,8 @@ ftrace_add_rec_direct(unsigned long ip, unsigned long addr, > static void call_direct_funcs(unsigned long ip, unsigned long pip, > struct ftrace_ops *ops, struct ftrace_regs *fregs) > { > - unsigned long addr; > + unsigned long addr = ops->direct_call; > > - addr = ftrace_find_rec_direct(ip); > if (!addr) > return; > > @@ -5375,6 +5374,7 @@ int register_ftrace_direct(struct ftrace_ops *ops, unsigned long addr) > ops->func = call_direct_funcs; > ops->flags = MULTI_FLAGS; > ops->trampoline = FTRACE_REGS_ADDR; > + ops->direct_call = addr; > > err = register_ftrace_function_nolock(ops); > > @@ -5445,6 +5445,7 @@ __modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr) > /* Enable the tmp_ops to have the same functions as the direct ops */ > ftrace_ops_init(&tmp_ops); > tmp_ops.func_hash = ops->func_hash; > + tmp_ops.direct_call = addr; > > err = register_ftrace_function_nolock(&tmp_ops); > if (err) > @@ -5466,6 +5467,7 @@ __modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr) > entry->direct = addr; > } > } > + ops->direct_call = addr; AFAICT we don't synchronize threads when installing the tmp_ops, so IIUC on arches with call_ops, there could be a a thread in the middle of ftrace_caller which has loaded the ops pointer from the patch-site, but hasn't yet loaded the ops::direct_func pointer, and could race with this assignment. Given that, I think this needs to be: WRITE_ONCE(ops->direct_call, addr); ... in order to avoid the risk of the store being torn, and the ftrace_caller trampoline loading a corrupted pointer. Other than that, this looks good to me! Thanks, Mark. > > mutex_unlock(&ftrace_lock); > > -- > 2.39.1.519.gcb327c4b5f-goog > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel