| Message ID | 20230316173811.1223508-6-revest@chromium.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Refactor ftrace direct call APIs | expand |
On Thu, Mar 16, 2023 at 06:38:09PM +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 <revest@chromium.org> > --- > include/linux/ftrace.h | 3 +++ > kernel/trace/ftrace.c | 7 +++++-- > 2 files changed, 8 insertions(+), 2 deletions(-) > > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h > index abee60865fc7..6a532dd6789e 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 33530198d1ca..66c91fa4b6ab 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -2582,9 +2582,8 @@ 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; nice, should it be read with READ_ONCE ? jirka > > - addr = ftrace_find_rec_direct(ip); > if (!addr) > return; > > @@ -5380,6 +5379,7 @@ 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); > > @@ -5454,6 +5454,7 @@ __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) > @@ -5475,6 +5476,8 @@ __modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr) > entry->direct = addr; > } > } > + /* Prevent store tearing if a trampoline concurrently accesses the value */ > + WRITE_ONCE(ops->direct_call, addr); > > mutex_unlock(&ftrace_lock); > > -- > 2.40.0.rc2.332.ga46443480c-goog >
On Sun, 19 Mar 2023 16:29:22 +0100 Jiri Olsa <olsajiri@gmail.com> wrote: > > +++ b/kernel/trace/ftrace.c > > @@ -2582,9 +2582,8 @@ 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; > > nice, should it be read with READ_ONCE ? Is there a "read tearing" too? -- Steve > > jirka > > > > > - addr = ftrace_find_rec_direct(ip); > > if (!addr) > > return; > > > > @@ -5380,6 +5379,7 @@ 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); > > > > @@ -5454,6 +5454,7 @@ __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) > > @@ -5475,6 +5476,8 @@ __modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr) > > entry->direct = addr; > > } > > } > > + /* Prevent store tearing if a trampoline concurrently accesses the value */ > > + WRITE_ONCE(ops->direct_call, addr); > > > > mutex_unlock(&ftrace_lock);
On Sun, Mar 19, 2023 at 01:54:43PM -0400, Steven Rostedt wrote: > On Sun, 19 Mar 2023 16:29:22 +0100 > Jiri Olsa <olsajiri@gmail.com> wrote: > > > > +++ b/kernel/trace/ftrace.c > > > @@ -2582,9 +2582,8 @@ 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; > > > > nice, should it be read with READ_ONCE ? > > Is there a "read tearing" too? don't know, saw the comment in __modify_ftrace_direct and got curious why it's not in here.. feel free to ignore, I'll look it up jirka > > -- Steve > > > > > jirka > > > > > > > > - addr = ftrace_find_rec_direct(ip); > > > if (!addr) > > > return; > > > > > > @@ -5380,6 +5379,7 @@ 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); > > > > > > @@ -5454,6 +5454,7 @@ __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) > > > @@ -5475,6 +5476,8 @@ __modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr) > > > entry->direct = addr; > > > } > > > } > > > + /* Prevent store tearing if a trampoline concurrently accesses the value */ > > > + WRITE_ONCE(ops->direct_call, addr); > > > > > > mutex_unlock(&ftrace_lock);
On Sun, Mar 19, 2023 at 7:55 PM Jiri Olsa <olsajiri@gmail.com> wrote: > > On Sun, Mar 19, 2023 at 01:54:43PM -0400, Steven Rostedt wrote: > > On Sun, 19 Mar 2023 16:29:22 +0100 > > Jiri Olsa <olsajiri@gmail.com> wrote: > > > > > > +++ b/kernel/trace/ftrace.c > > > > @@ -2582,9 +2582,8 @@ 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; > > > > > > nice, should it be read with READ_ONCE ? > > > > Is there a "read tearing" too? > > don't know, saw the comment in __modify_ftrace_direct and got curious > why it's not in here.. feel free to ignore, I'll look it up > > jirka Mhh, that's a good question. Based on my current understanding, it seems that it should have a READ_ONCE, indeed. However, I'd like Mark to confirm/deny this. :) If this should be a READ_ONCE, I can send a v2 series with this fixed.
On Mon, 20 Mar 2023 18:45:08 +0100 Florent Revest <revest@chromium.org> wrote: > On Sun, Mar 19, 2023 at 7:55 PM Jiri Olsa <olsajiri@gmail.com> wrote: > > > > On Sun, Mar 19, 2023 at 01:54:43PM -0400, Steven Rostedt wrote: > > > On Sun, 19 Mar 2023 16:29:22 +0100 > > > Jiri Olsa <olsajiri@gmail.com> wrote: > > > > > > > > +++ b/kernel/trace/ftrace.c > > > > > @@ -2582,9 +2582,8 @@ 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; > > > > > > > > nice, should it be read with READ_ONCE ? > > > > > > Is there a "read tearing" too? > > > > don't know, saw the comment in __modify_ftrace_direct and got curious > > why it's not in here.. feel free to ignore, I'll look it up > > > > jirka > > Mhh, that's a good question. Based on my current understanding, it > seems that it should have a READ_ONCE, indeed. However, I'd like Mark > to confirm/deny this. :) > > If this should be a READ_ONCE, I can send a v2 series with this fixed. After re-reading: https://lwn.net/Articles/793253/ I think we should add the READ_ONCE() (also with a comment). -- Steve
On Mon, Mar 20, 2023 at 05:31:55PM -0400, Steven Rostedt wrote: > On Mon, 20 Mar 2023 18:45:08 +0100 > Florent Revest <revest@chromium.org> wrote: > > > On Sun, Mar 19, 2023 at 7:55 PM Jiri Olsa <olsajiri@gmail.com> wrote: > > > > > > On Sun, Mar 19, 2023 at 01:54:43PM -0400, Steven Rostedt wrote: > > > > On Sun, 19 Mar 2023 16:29:22 +0100 > > > > Jiri Olsa <olsajiri@gmail.com> wrote: > > > > > > > > > > +++ b/kernel/trace/ftrace.c > > > > > > @@ -2582,9 +2582,8 @@ 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; > > > > > > > > > > nice, should it be read with READ_ONCE ? > > > > > > > > Is there a "read tearing" too? > > > > > > don't know, saw the comment in __modify_ftrace_direct and got curious > > > why it's not in here.. feel free to ignore, I'll look it up > > > > > > jirka > > > > Mhh, that's a good question. Based on my current understanding, it > > seems that it should have a READ_ONCE, indeed. However, I'd like Mark > > to confirm/deny this. :) > > > > If this should be a READ_ONCE, I can send a v2 series with this fixed. > > After re-reading: https://lwn.net/Articles/793253/ > > I think we should add the READ_ONCE() (also with a comment). I think so, too. AFAICT there's nothing that prevents __modify_ftrace_direct() and call_direct_funcs() from concurrently accessing ftrace_ops::direct_call, so we need READ_ONCE() in call_direct_funcs() to prevent load tearing and other issues mentioned in the article linked above. The existing code has a similar pattern where __modify_ftrace_direct() and ftrace_find_rec_direct() access ftrace_func_entry::direct concurrently. Do we want a preparatory patch fixing that for stable? Thanks, Mark.
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h index abee60865fc7..6a532dd6789e 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 33530198d1ca..66c91fa4b6ab 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -2582,9 +2582,8 @@ 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; @@ -5380,6 +5379,7 @@ 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); @@ -5454,6 +5454,7 @@ __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) @@ -5475,6 +5476,8 @@ __modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr) entry->direct = addr; } } + /* Prevent store tearing if a trampoline concurrently accesses the value */ + WRITE_ONCE(ops->direct_call, addr); mutex_unlock(&ftrace_lock);
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 <revest@chromium.org> --- include/linux/ftrace.h | 3 +++ kernel/trace/ftrace.c | 7 +++++-- 2 files changed, 8 insertions(+), 2 deletions(-)