On Tue, Apr 04, 2023 at 12:02:54AM +0200, Jiri Olsa wrote: > Artem reported suspicious RCU usage [1]. The reason is that verifier > calls find_kallsyms_symbol_value with preemption enabled which will > trigger suspicious RCU usage warning in rcu_dereference_sched call. > > Disabling preemption in find_kallsyms_symbol_value and adding > __find_kallsyms_symbol_value function. Tested-by: Artem Savkov <asavkov@xxxxxxxxxx> > Fixes: 31bf1dbccfb0 ("bpf: Fix attaching fentry/fexit/fmod_ret/lsm to modules") > [1] https://lore.kernel.org/bpf/ZBrPMkv8YVRiWwCR@xxxxxxxxxxxxxxxxxxxxxxxx/ > Reported-by: Artem Savkov <asavkov@xxxxxxxxxx> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx> > --- > kernel/module/kallsyms.c | 16 +++++++++++++--- > 1 file changed, 13 insertions(+), 3 deletions(-) > > diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c > index ab2376a1be88..bdc911dbcde5 100644 > --- a/kernel/module/kallsyms.c > +++ b/kernel/module/kallsyms.c > @@ -442,7 +442,7 @@ int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type, > } > > /* Given a module and name of symbol, find and return the symbol's value */ > -unsigned long find_kallsyms_symbol_value(struct module *mod, const char *name) > +static unsigned long __find_kallsyms_symbol_value(struct module *mod, const char *name) > { > unsigned int i; > struct mod_kallsyms *kallsyms = rcu_dereference_sched(mod->kallsyms); > @@ -466,7 +466,7 @@ static unsigned long __module_kallsyms_lookup_name(const char *name) > if (colon) { > mod = find_module_all(name, colon - name, false); > if (mod) > - return find_kallsyms_symbol_value(mod, colon + 1); > + return __find_kallsyms_symbol_value(mod, colon + 1); > return 0; > } > > @@ -475,7 +475,7 @@ static unsigned long __module_kallsyms_lookup_name(const char *name) > > if (mod->state == MODULE_STATE_UNFORMED) > continue; > - ret = find_kallsyms_symbol_value(mod, name); > + ret = __find_kallsyms_symbol_value(mod, name); > if (ret) > return ret; > } > @@ -494,6 +494,16 @@ unsigned long module_kallsyms_lookup_name(const char *name) > return ret; > } > > +unsigned long find_kallsyms_symbol_value(struct module *mod, const char *name) > +{ > + unsigned long ret; > + > + preempt_disable(); > + ret = __find_kallsyms_symbol_value(mod, name); > + preempt_enable(); > + return ret; > +} > + > int module_kallsyms_on_each_symbol(const char *modname, > int (*fn)(void *, const char *, > struct module *, unsigned long), > -- > 2.39.2 > -- Artem