Fix race between cat /proc/slab_allocators and rmmod

Same story as with cat /proc/*/wchan race vs rmmod race, only
/proc/slab_allocators want more info than just symbol name.

Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

5 files changed, 61 insertions, 7 deletions

diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
index ae0117a95cfd..12178d2c882b 100644
--- a/include/linux/kallsyms.h
+++ b/include/linux/kallsyms.h
@@ -31,6 +31,7 @@ extern int sprint_symbol(char *buffer, unsigned long address);
 extern void __print_symbol(const char *fmt, unsigned long address);
 
 int lookup_symbol_name(unsigned long addr, char *symname);
+int lookup_symbol_attrs(unsigned long addr, unsigned long *size, unsigned long *offset, char *modname, char *name);
 
 #else /* !CONFIG_KALLSYMS */
 
@@ -65,6 +66,11 @@ static inline int lookup_symbol_name(unsigned long addr, char *symname)
         return -ERANGE;
 }
 
+static inline int lookup_symbol_attrs(unsigned long addr, unsigned long *size, unsigned long *offset, char *modname, char *name)
+{
+        return -ERANGE;
+}
+
 /* Stupid that this does nothing, but I didn't create this mess. */
 #define __print_symbol(fmt, addr)
 #endif /*CONFIG_KALLSYMS*/
diff --git a/include/linux/module.h b/include/linux/module.h
index 099ae5932c68..6d3dc9c4ff96 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -455,6 +455,7 @@ const char *module_address_lookup(unsigned long addr,
                                   unsigned long *offset,
                                   char **modname);
 int lookup_module_symbol_name(unsigned long addr, char *symname);
+int lookup_module_symbol_attrs(unsigned long addr, unsigned long *size, unsigned long *offset, char *modname, char *name);
 
 /* For extable.c to search modules' exception tables. */
 const struct exception_table_entry *search_module_extables(unsigned long addr);
@@ -531,6 +532,11 @@ static inline int lookup_module_symbol_name(unsigned long addr, char *symname)
         return -ERANGE;
 }
 
+static inline int lookup_module_symbol_attrs(unsigned long addr, unsigned long *size, unsigned long *offset, char *modname, char *name)
+{
+        return -ERANGE;
+}
+
 static inline int module_get_kallsym(unsigned int symnum, unsigned long *value,
                                         char *type, char *name,
                                         char *module_name, int *exported)
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 4e2ec191a127..c36581b40c04 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -286,6 +286,25 @@ int lookup_symbol_name(unsigned long addr, char *symname)
         return lookup_module_symbol_name(addr, symname);
 }
 
+int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
+                        unsigned long *offset, char *modname, char *name)
+{
+        name[0] = '\0';
+        name[KSYM_NAME_LEN] = '\0';
+
+        if (is_ksym_addr(addr)) {
+                unsigned long pos;
+
+                pos = get_symbol_pos(addr, size, offset);
+                /* Grab name */
+                kallsyms_expand_symbol(get_symbol_offset(pos), name);
+                modname[0] = '\0';
+                return 0;
+        }
+        /* see if it's in a module */
+        return lookup_module_symbol_attrs(addr, size, offset, modname, name);
+}
+
 /* Look up a kernel symbol and return it in a text buffer. */
 int sprint_symbol(char *buffer, unsigned long address)
 {
diff --git a/kernel/module.c b/kernel/module.c
index 3da76ad32d78..d36e45477fac 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2149,6 +2149,33 @@ out:
         return -ERANGE;
 }
 
+int lookup_module_symbol_attrs(unsigned long addr, unsigned long *size,
+                        unsigned long *offset, char *modname, char *name)
+{
+        struct module *mod;
+
+        mutex_lock(&module_mutex);
+        list_for_each_entry(mod, &modules, list) {
+                if (within(addr, mod->module_init, mod->init_size) ||
+                    within(addr, mod->module_core, mod->core_size)) {
+                        const char *sym;
+
+                        sym = get_ksymbol(mod, addr, size, offset);
+                        if (!sym)
+                                goto out;
+                        if (modname)
+                                strlcpy(modname, mod->name, MODULE_NAME_LEN + 1);
+                        if (name)
+                                strlcpy(name, sym, KSYM_NAME_LEN + 1);
+                        mutex_unlock(&module_mutex);
+                        return 0;
+                }
+        }
+out:
+        mutex_unlock(&module_mutex);
+        return -ERANGE;
+}
+
 int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
                         char *name, char *module_name, int *exported)
 {
diff --git a/mm/slab.c b/mm/slab.c
index 1115e2065bfc..acda7e2d66e4 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -4432,16 +4432,12 @@ static void handle_slab(unsigned long *n, struct kmem_cache *c, struct slab *s)
 static void show_symbol(struct seq_file *m, unsigned long address)
 {
 #ifdef CONFIG_KALLSYMS
-        char *modname;
-        const char *name;
         unsigned long offset, size;
-        char namebuf[KSYM_NAME_LEN+1];
-
-        name = kallsyms_lookup(address, &size, &offset, &modname, namebuf);
+        char modname[MODULE_NAME_LEN + 1], name[KSYM_NAME_LEN + 1];
 
-        if (name) {
+        if (lookup_symbol_attrs(address, &size, &offset, modname, name) == 0) {
                 seq_printf(m, "%s+%#lx/%#lx", name, offset, size);
-                if (modname)
+                if (modname[0])
                         seq_printf(m, " [%s]", modname);
                 return;
         }