[PATCH] arm:unwind: fix incorrect backtrace with unwind_table

[chenzefeng]

For arm, if the CONFIG_ARM_UNWIND is open, when insmod a module,
the init section add to the unwind_table, the code path as follow:
        load_module
        --->post_relocation
        ------->module_finalize
        ----------->maps[ARM_SEC_INIT].txt_sec = s
        ----------->unwind_table_add

Later if load_module success, the init section's memory will be
vfree, the code path as follow:
        load_module
        --->do_init_module
        ------->freeinit->module_init = mod->init_layout.base
        ------->schedule_work(&init_free_wq)
        ----------->do_free_init
        --------------->vfree(freeinit->module_init)

But after the init section's had been vfree, but it's unwind_table
is not removed.

The issue as follow:
When insmod module A, the system alloc the "Addr1" for it's init
text section, and add it to the unwind_table list, after insmod
success, the "Addr1" would be vfreed.
Unfortunately, later insmod module B, the system alloc the "Addr1"
for it's text section, and add it to the unwind_table list, too.
And we dumpstack in module B, we may get a incorrect backtrace.

Signed-off-by: chenzefeng <chenzefe...@huawei.com>
---
 arch/arm/kernel/module.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c
index deef17f..438ed67 100644
--- a/arch/arm/kernel/module.c
+++ b/arch/arm/kernel/module.c
@@ -410,7 +410,20 @@ int module_finalize(const Elf32_Ehdr *hdr, const Elf_Shdr 
*sechdrs,
        int i;
 
        for (i = 0; i < ARM_SEC_MAX; i++)
-               if (mod->arch.unwind[i])
+               if (mod->arch.unwind[i]) {
                        unwind_table_del(mod->arch.unwind[i]);
+                       mod->arch.unwind[i] = NULL;
+               }
+#endif
+}
+
+void
+module_arch_freeing_init(struct module *mod)
+{
+#ifdef CONFIG_ARM_UNWIND
+       if (mod->arch.unwind[ARM_SEC_INIT]) {
+               unwind_table_del(mod->arch.unwind[ARM_SEC_INIT]);
+               mod->arch.unwind[ARM_SEC_INIT] = NULL;
+       }
 #endif
 }
-- 
1.8.5.6