| Message ID | 20220310102413.3438665-11-atomlin@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | module: core code clean up | expand |
On Thu, 10 Mar 2022 10:24:09 +0000 Aaron Tomlin <atomlin@redhat.com> wrote: > No functional change. There most definitely is a functional change here. > > The purpose of this patch is to address the various Sparse warnings > due to the incorrect dereference/or access of an __rcu pointer. > > Signed-off-by: Aaron Tomlin <atomlin@redhat.com> > --- > kernel/module/kallsyms.c | 34 ++++++++++++++++++++++------------ > 1 file changed, 22 insertions(+), 12 deletions(-) > > diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c > index 1b0780e20aab..a3da0686a2a6 100644 > --- a/kernel/module/kallsyms.c > +++ b/kernel/module/kallsyms.c > @@ -171,14 +171,17 @@ void add_kallsyms(struct module *mod, const struct load_info *info) > Elf_Shdr *symsec = &info->sechdrs[info->index.sym]; > > /* Set up to point into init section. */ > - mod->kallsyms = mod->init_layout.base + info->mod_kallsyms_init_off; > + mod->kallsyms = (void __rcu *)mod->init_layout.base + > + info->mod_kallsyms_init_off; > > + preempt_disable(); ^^^^^^^^^^^^^^^^^^ > /* The following is safe since this pointer cannot change */ > - mod->kallsyms->symtab = (void *)symsec->sh_addr; > - mod->kallsyms->num_symtab = symsec->sh_size / sizeof(Elf_Sym); > + rcu_dereference_sched(mod->kallsyms)->symtab = (void *)symsec->sh_addr; > + rcu_dereference_sched(mod->kallsyms)->num_symtab = symsec->sh_size / sizeof(Elf_Sym); > /* Make sure we get permanent strtab: don't use info->strtab. */ > - mod->kallsyms->strtab = (void *)info->sechdrs[info->index.str].sh_addr; > - mod->kallsyms->typetab = mod->init_layout.base + info->init_typeoffs; > + rcu_dereference_sched(mod->kallsyms)->strtab = > + (void *)info->sechdrs[info->index.str].sh_addr; > + rcu_dereference_sched(mod->kallsyms)->typetab = mod->init_layout.base + info->init_typeoffs; > > /* > * Now populate the cut down core kallsyms for after init > @@ -187,20 +190,22 @@ void add_kallsyms(struct module *mod, const struct load_info *info) > mod->core_kallsyms.symtab = dst = mod->core_layout.base + info->symoffs; > mod->core_kallsyms.strtab = s = mod->core_layout.base + info->stroffs; > mod->core_kallsyms.typetab = mod->core_layout.base + info->core_typeoffs; > - src = mod->kallsyms->symtab; > - for (ndst = i = 0; i < mod->kallsyms->num_symtab; i++) { > - mod->kallsyms->typetab[i] = elf_type(src + i, info); > + src = rcu_dereference_sched(mod->kallsyms)->symtab; > + for (ndst = i = 0; i < rcu_dereference_sched(mod->kallsyms)->num_symtab; i++) { How big is this loop? > + rcu_dereference_sched(mod->kallsyms)->typetab[i] = elf_type(src + i, info); > if (i == 0 || is_livepatch_module(mod) || > is_core_symbol(src + i, info->sechdrs, info->hdr->e_shnum, > info->index.pcpu)) { > mod->core_kallsyms.typetab[ndst] = > - mod->kallsyms->typetab[i]; > + rcu_dereference_sched(mod->kallsyms)->typetab[i]; > dst[ndst] = src[i]; > dst[ndst++].st_name = s - mod->core_kallsyms.strtab; > - s += strscpy(s, &mod->kallsyms->strtab[src[i].st_name], > + s += strscpy(s, > + &rcu_dereference_sched(mod->kallsyms)->strtab[src[i].st_name], > KSYM_NAME_LEN) + 1; > } > } > + preempt_enable(); ^^^^^^^^^^^^^^^^^ This just introduced an unbounded latency and will fail PREEMPT_RT. -- Steve > mod->core_kallsyms.num_symtab = ndst; > } > > @@ -478,11 +483,16 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *, > > mutex_lock(&module_mutex); > list_for_each_entry(mod, &modules, list) { > - /* We hold module_mutex: no need for rcu_dereference_sched */ > - struct mod_kallsyms *kallsyms = mod->kallsyms; > + struct mod_kallsyms *kallsyms; > > if (mod->state == MODULE_STATE_UNFORMED) > continue; > + > + /* Use rcu_dereference_sched() to remain compliant with the sparse tool */ > + preempt_disable(); > + kallsyms = rcu_dereference_sched(mod->kallsyms); > + preempt_enable(); > + > for (i = 0; i < kallsyms->num_symtab; i++) { > const Elf_Sym *sym = &kallsyms->symtab[i]; >
On Mon 2022-06-27 23:56 -0400, Steven Rostedt wrote: > > + preempt_enable(); > > ^^^^^^^^^^^^^^^^^ > > This just introduced an unbounded latency and will fail PREEMPT_RT. > Hi Steve, Sorry about that! If I understand correctly, there is absolutely no need to explicitly disable preemption in this context. I will use: rcu_read_lock() and rcu_read_unlock(), respectively, which will then be suitable for the preemptible RCU implementation. Kind regards,
On Tue, 28 Jun 2022 17:21:22 +0100 Aaron Tomlin <atomlin@redhat.com> wrote: > If I understand correctly, there is absolutely no need to explicitly > disable preemption in this context. I will use: rcu_read_lock() and > rcu_read_unlock(), respectively, which will then be suitable for the > preemptible RCU implementation. Yes, thank you very much :-) -- Steve
diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c index 1b0780e20aab..a3da0686a2a6 100644 --- a/kernel/module/kallsyms.c +++ b/kernel/module/kallsyms.c @@ -171,14 +171,17 @@ void add_kallsyms(struct module *mod, const struct load_info *info) Elf_Shdr *symsec = &info->sechdrs[info->index.sym]; /* Set up to point into init section. */ - mod->kallsyms = mod->init_layout.base + info->mod_kallsyms_init_off; + mod->kallsyms = (void __rcu *)mod->init_layout.base + + info->mod_kallsyms_init_off; + preempt_disable(); /* The following is safe since this pointer cannot change */ - mod->kallsyms->symtab = (void *)symsec->sh_addr; - mod->kallsyms->num_symtab = symsec->sh_size / sizeof(Elf_Sym); + rcu_dereference_sched(mod->kallsyms)->symtab = (void *)symsec->sh_addr; + rcu_dereference_sched(mod->kallsyms)->num_symtab = symsec->sh_size / sizeof(Elf_Sym); /* Make sure we get permanent strtab: don't use info->strtab. */ - mod->kallsyms->strtab = (void *)info->sechdrs[info->index.str].sh_addr; - mod->kallsyms->typetab = mod->init_layout.base + info->init_typeoffs; + rcu_dereference_sched(mod->kallsyms)->strtab = + (void *)info->sechdrs[info->index.str].sh_addr; + rcu_dereference_sched(mod->kallsyms)->typetab = mod->init_layout.base + info->init_typeoffs; /* * Now populate the cut down core kallsyms for after init @@ -187,20 +190,22 @@ void add_kallsyms(struct module *mod, const struct load_info *info) mod->core_kallsyms.symtab = dst = mod->core_layout.base + info->symoffs; mod->core_kallsyms.strtab = s = mod->core_layout.base + info->stroffs; mod->core_kallsyms.typetab = mod->core_layout.base + info->core_typeoffs; - src = mod->kallsyms->symtab; - for (ndst = i = 0; i < mod->kallsyms->num_symtab; i++) { - mod->kallsyms->typetab[i] = elf_type(src + i, info); + src = rcu_dereference_sched(mod->kallsyms)->symtab; + for (ndst = i = 0; i < rcu_dereference_sched(mod->kallsyms)->num_symtab; i++) { + rcu_dereference_sched(mod->kallsyms)->typetab[i] = elf_type(src + i, info); if (i == 0 || is_livepatch_module(mod) || is_core_symbol(src + i, info->sechdrs, info->hdr->e_shnum, info->index.pcpu)) { mod->core_kallsyms.typetab[ndst] = - mod->kallsyms->typetab[i]; + rcu_dereference_sched(mod->kallsyms)->typetab[i]; dst[ndst] = src[i]; dst[ndst++].st_name = s - mod->core_kallsyms.strtab; - s += strscpy(s, &mod->kallsyms->strtab[src[i].st_name], + s += strscpy(s, + &rcu_dereference_sched(mod->kallsyms)->strtab[src[i].st_name], KSYM_NAME_LEN) + 1; } } + preempt_enable(); mod->core_kallsyms.num_symtab = ndst; } @@ -478,11 +483,16 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *, mutex_lock(&module_mutex); list_for_each_entry(mod, &modules, list) { - /* We hold module_mutex: no need for rcu_dereference_sched */ - struct mod_kallsyms *kallsyms = mod->kallsyms; + struct mod_kallsyms *kallsyms; if (mod->state == MODULE_STATE_UNFORMED) continue; + + /* Use rcu_dereference_sched() to remain compliant with the sparse tool */ + preempt_disable(); + kallsyms = rcu_dereference_sched(mod->kallsyms); + preempt_enable(); + for (i = 0; i < kallsyms->num_symtab; i++) { const Elf_Sym *sym = &kallsyms->symtab[i];
No functional change. The purpose of this patch is to address the various Sparse warnings due to the incorrect dereference/or access of an __rcu pointer. Signed-off-by: Aaron Tomlin <atomlin@redhat.com> --- kernel/module/kallsyms.c | 34 ++++++++++++++++++++++------------ 1 file changed, 22 insertions(+), 12 deletions(-)