[PATCH] fix error handling in load_module()

[Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>]

Hi Rusty,

	During our testing following call trace was seen. The testcase was
to compile the kernel based on the distro config and try to insert all the
modules compiled.

#!/bin/sh

for module in `modprobe -l | tr '\n' ' '`
do
	insert_module=`basename $module .ko`
	modprobe -v $insert_module
done

freq_table sputrace hvcserver axonram pmi ipv6 fuse ehea ib
Sep  7 15:46:04 mjs22lp5 kernel: mveth ibmvscsic scsi_transport_srp scsi_tgt
Sep  7 15:46:04 mjs22lp5 kernel: NIP: c0000000000ebba0 LR: c0000000000ee79c CTR: 0000000000000000
Sep  7 15:46:04 mjs22lp5 kernel: REGS: c00000002c90b8e0 TRAP: 0700 Tainted: P      D     (2.6.31-rc8)
Sep  7 15:46:04 mjs22lp5 kernel: MSR: 8000000000029032 <EE,ME,CE,IR,DR> CR: 24222488  XER: 00000008
Sep  7 15:46:04 mjs22lp5 kernel: TASK = c00000002ff40000[9062] 'modprobe' THREAD: c00000002c908000 CPU: 0
Sep  7 15:46:04 mjs22lp5 kernel: GPR00: 0000000000000010 c00000002c90bb60 c000000001421e68 0000000000000000
Sep  7 15:46:04 mjs22lp5 kernel: GPR04: c000000000691a5c c00000000009f5c4 0000000000000000 c0000000167f6630
Sep  7 15:46:04 mjs22lp5 kernel: GPR08: c0000000167f72a4 000000000000031f c000000000bb9580 000000000000031e
Sep  7 15:46:04 mjs22lp5 kernel: GPR12: 800000000631b800 c0000000015a2600 0000000000000000 0000000000000000
Sep  7 15:46:04 mjs22lp5 kernel: GPR16: 0000000000000033 d00000000fb1f6d0 d00000000fb1fe50 000000000000000e
Sep  7 15:46:04 mjs22lp5 kernel: GPR20: d00000000fb1efb8 d00000000fb62260 d00000000fb00000 8000000000000000
Sep  7 15:46:04 mjs22lp5 kernel: GPR24: 0000000000000004 d00000000fb1f190 0000000000000035 fffffffffffffff4
Sep  7 15:46:04 mjs22lp5 kernel: GPR28: 0000000000000000 000000000000031e c00000000137def8 c00000002c90bb60
Sep  7 15:46:04 mjs22lp5 kernel: NIP [c0000000000ebba0] .percpu_modfree+0xe8/0x210
Sep  7 15:46:04 mjs22lp5 kernel: LR [c0000000000ee79c] .load_module+0x14f8/0x1650
Sep  7 15:46:04 mjs22lp5 kernel: Call Trace:
Sep  7 15:46:04 mjs22lp5 kernel: [c00000002c90bb60] [c00000002c90bc00] 0xc00000002c90bc00 (unreliable)
Sep  7 15:46:04 mjs22lp5 kernel: [c00000002c90bc00] [c0000000000ee79c] .load_module+0x14f8/0x1650
Sep  7 15:46:04 mjs22lp5 kernel: [c00000002c90bd90] [c0000000000ee988] .SyS_init_module+0x94/0x2ac
Sep  7 15:46:04 mjs22lp5 kernel: [c00000002c90be30] [c0000000000084dc] syscall_exit+0x0/0x40
Sep  7 15:46:04 mjs22lp5 kernel: Instruction dump:
Sep  7 15:46:05 mjs22lp5 kernel: 48000038 e8080006 793d0020 39080004 78090020 2f800000 409c000c 7c0000d0
Sep  7 15:46:05 mjs22lp5 kernel: 78090020 7d4a4a14 393d0001 4200ffb0 <0fe00000> 48000000 38a30001 7f83e378
Sep  7 15:46:05 mjs22lp5 kernel: ---[ end trace 3c8bbdf1034c7f0d ]---

Once the percpu_modalloc fails, percpu_modfree(mod->refptr) is called on a NULL pointer.
We try calling it on a NULL pointer. The following patch fixes the problem by introducing 
a check for mod->refptr before calling percpu_modfree.

Signed-off-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
--
 kernel/module.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index 2d53718..7f89258 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2379,7 +2379,8 @@ static noinline struct module *load_module(void __user *umod,
 	module_unload_free(mod);
 #if defined(CONFIG_MODULE_UNLOAD) && defined(CONFIG_SMP)
  free_init:
-	percpu_modfree(mod->refptr);
+	if (mod->refptr)
+		percpu_modfree(mod->refptr);
 #endif
 	module_free(mod, mod->module_init);
  free_core:
			
			Kamalesh