From: Rusty Russell on
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(a)>
Signed-off-by: Rusty Russell <rusty(a)>
Cc: Tejun Heo <tj(a)>
Cc: Masami Hiramatsu <mhiramat(a)>
Tested-by: "Rafael J. Wysocki" <rjw(a)>
kernel/module.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/module.c b/kernel/module.c
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2031,6 +2031,7 @@ static noinline struct module *load_modu
long err = 0;
void *ptr = NULL; /* Stops spurious gcc warning */
unsigned long symoffs, stroffs, *strmap;
+ void __percpu *percpu;

mm_segment_t old_fs;

@@ -2175,6 +2176,8 @@ static noinline struct module *load_modu
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
@@ -2480,7 +2483,7 @@ static noinline struct module *load_modu
module_free(mod, mod->module_core);
/* mod will be freed with core. Don't access it beyond this line! */
- percpu_modfree(mod);
+ free_percpu(percpu);
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