Looking at add_kallsyms(), there is absolutely no need to explicitly
disable preemption. Before kallsyms-specific data is prepared/or set-up, we
ensure that the unformed module is known to be unique i.e. does not already
exist (see load_module()). Therefore, we can use the common RCU primitive
as this section of code can be pre-empted. In other words, it is safe to be
re-scheduled, in this context.
Reported-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Fixes: 08126db5ff73 ("module: kallsyms: Fix suspicious rcu usage")
Signed-off-by: Aaron Tomlin <atomlin@xxxxxxxxxx>
---
kernel/module/kallsyms.c | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)
diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
index 3e11523bc6f6..b16ff36b4b71 100644
--- a/kernel/module/kallsyms.c
+++ b/kernel/module/kallsyms.c
@@ -174,14 +174,14 @@ void add_kallsyms(struct module *mod, const struct load_info *info)
mod->kallsyms = (void __rcu *)mod->init_layout.base +
info->mod_kallsyms_init_off;
- preempt_disable();
+ rcu_read_lock();
/* The following is safe since this pointer cannot change */
- rcu_dereference_sched(mod->kallsyms)->symtab = (void *)symsec->sh_addr;
- rcu_dereference_sched(mod->kallsyms)->num_symtab = symsec->sh_size / sizeof(Elf_Sym);
+ rcu_dereference(mod->kallsyms)->symtab = (void *)symsec->sh_addr;
+ rcu_dereference(mod->kallsyms)->num_symtab = symsec->sh_size / sizeof(Elf_Sym);
/* Make sure we get permanent strtab: don't use info->strtab. */
- rcu_dereference_sched(mod->kallsyms)->strtab =
+ rcu_dereference(mod->kallsyms)->strtab =
(void *)info->sechdrs[info->index.str].sh_addr;
- rcu_dereference_sched(mod->kallsyms)->typetab = mod->init_layout.base + info->init_typeoffs;
+ rcu_dereference(mod->kallsyms)->typetab = mod->init_layout.base + info->init_typeoffs;
/*
* Now populate the cut down core kallsyms for after init
@@ -190,22 +190,22 @@ void add_kallsyms(struct module *mod, const struct load_info *info)
mod->core_kallsyms.symtab = dst = mod->data_layout.base + info->symoffs;
mod->core_kallsyms.strtab = s = mod->data_layout.base + info->stroffs;
mod->core_kallsyms.typetab = mod->data_layout.base + info->core_typeoffs;
- 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);
+ src = rcu_dereference(mod->kallsyms)->symtab;
+ for (ndst = i = 0; i < rcu_dereference(mod->kallsyms)->num_symtab; i++) {
+ rcu_dereference(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] =
- rcu_dereference_sched(mod->kallsyms)->typetab[i];
+ rcu_dereference(mod->kallsyms)->typetab[i];
dst[ndst] = src[i];
dst[ndst++].st_name = s - mod->core_kallsyms.strtab;
s += strscpy(s,
- &rcu_dereference_sched(mod->kallsyms)->strtab[src[i].st_name],
+ &rcu_dereference(mod->kallsyms)->strtab[src[i].st_name],
KSYM_NAME_LEN) + 1;
}
}
- preempt_enable();
+ rcu_read_unlock();
mod->core_kallsyms.num_symtab = ndst;
}
--
2.34.3
