module: fix reference to mod->percpu after freeing module.

Rafael sees a sometimes crash at precpu_modfree from kernel/module.c; it
only occurred with another (since-reverted) patch, but that patch simply
changed timing to uncover this bug, it was otherwise unrelated.

The comment about the mod being freed is self-explanatory, but neither
Tejun nor I read it.  This bug was introduced in 259354deaa, after it
had previously been fixed in 6e2b75740b.  How embarrassing.

Reported-by: "Rafael J. Wysocki" <rjw@sisk.pl>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Embarrassingly-Acked-by: Tejun Heo <tj@kernel.org>
Cc: Masami Hiramatsu <mhiramat@redhat.com>
Tested-by: "Rafael J. Wysocki" <rjw@sisk.pl>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/kernel/module.c b/kernel/module.c
index 333fbcc96978..d806e00e4450 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2014,6 +2014,7 @@ static noinline struct module *load_module(void __user *umod,
         long err = 0;
         void *ptr = NULL; /* Stops spurious gcc warning */
         unsigned long symoffs, stroffs, *strmap;
+        void __percpu *percpu;
 
         mm_segment_t old_fs;
 
@@ -2158,6 +2159,8 @@ static noinline struct module *load_module(void __user *umod,
                         goto free_mod;
                 sechdrs[pcpuindex].sh_flags &= ~(unsigned long)SHF_ALLOC;
         }
+        /* Keep this around for failure path. */
+        percpu = mod_percpu(mod);
 
         /* Determine total sizes, and put offsets in sh_entsize.  For now
            this is done generically; there doesn't appear to be any
@@ -2463,7 +2466,7 @@ static noinline struct module *load_module(void __user *umod,
         module_free(mod, mod->module_core);
         /* mod will be freed with core. Don't access it beyond this line! */
  free_percpu:
-        percpu_modfree(mod);
+        free_percpu(percpu);
  free_mod:
         kfree(args);
         kfree(strmap);