If kobject state is not initialized, then its not even certain that kobject'name is initialized. Hence when accessing the kobject's name tread carefully.
A stupid module test like https://github.com/srikard/tests/blob/master/modules/kobject_test.c can panic the system. With patch: We will see the correct warning. [ 2058.129913] ------------[ cut here ]------------ [ 2058.129919] kobject: ' ' (00000000ad405b63): is not initialized, yet kobject_get() is being called. [ 2058.129938] WARNING: CPU: 58 PID: 18529 at /home/srikar/work/linux.git/lib/kobject.c:620 kobject_get+0x90/0xb0 [ 2058.129946] Modules linked in: kobject_test(OE+) uio_pdrv_genirq(E) uio(E) leds_powernv(E) powernv_op_panel(E) ipmi_powernv(E) ipmi_devintf(E) powernv_rng(E) ibmpowernv(E) ipmi_msghandler(E) vmx_crypto(E) crct10dif_vpmsum(E) sch_fq_codel(E) ip_tables(E) x_tables(E) autofs4(E) ses enclosure scsi_transport_sas mlx4_ib mlx4_en ib_core lpfc crc32c_vpmsum mlx4_core nvmet_fc nvmet nvme_fc ipr nvme_fabrics devlink scsi_transport_fc tg3 [last unloaded: module_test] [ 2058.130014] CPU: 58 PID: 18529 Comm: insmod Tainted: G W OEL 4.18.0-master+ #3 [ 2058.130022] NIP: c000000000d5f530 LR: c000000000d5f52c CTR: 0000000000000000 [ 2058.130029] REGS: c000002fd32f3640 TRAP: 0700 Tainted: G W OEL (4.18.0-master+) [ 2058.130036] MSR: 9000000002029033 <SF,HV,VEC,EE,ME,IR,DR,RI,LE> CR: 48002282 XER: 20000000 [ 2058.130054] CFAR: c000000000114e10 IRQMASK: 0 GPR00: c000000000d5f52c c000002fd32f38c0 c0000000017bc200 0000000000000057 GPR04: 0000000000000001 000000000000107e 9000000002009033 00000000000000f2 GPR08: 0000000000000007 0000000000000007 0000000000000001 9000000002001003 GPR12: 0000000000002200 c000002ffffe0d00 0000000000000000 0000000000000000 GPR16: 0000000000000000 c0000000001e92e0 0000000000000000 0000000000000100 GPR20: 0000000000000001 c000000001662e60 c000000001662ed8 c000002feb4114a0 GPR24: 0000000000000001 c000000000dbd438 c000000001662ea0 c000000001662ec0 GPR28: c000002fe5f0cea0 d00000001ded03d0 c000002fd32f39a0 c000002fd32f39a0 [ 2058.130133] NIP [c000000000d5f530] kobject_get+0x90/0xb0 [ 2058.130140] LR [c000000000d5f52c] kobject_get+0x8c/0xb0 [ 2058.130146] Call Trace: [ 2058.130150] [c000002fd32f38c0] [c000000000d5f52c] kobject_get+0x8c/0xb0 (unreliable) [ 2058.130159] [c000002fd32f3940] [d00000001ded0088] kobject_test_init+0x80/0xb0 [kobject_test] [ 2058.130168] [c000002fd32f39f0] [c0000000000101f8] do_one_initcall+0x58/0x240 [ 2058.130178] [c000002fd32f3ab0] [c0000000001ef2b0] do_init_module+0x90/0x260 [ 2058.130186] [c000002fd32f3b40] [c0000000001edec8] load_module+0x2d88/0x3320 [ 2058.130193] [c000002fd32f3d20] [c0000000001ee764] sys_finit_module+0xc4/0x130 [ 2058.130204] [c000002fd32f3e30] [c00000000000b288] system_call+0x5c/0x70 [ 2058.130210] Instruction dump: [ 2058.130215] e89f0000 4b5b4c15 60000000 2f830000 419e0030 3c82ff8c 388491e0 3c62ff90 [ 2058.130228] 7fe5fb78 3863e9b0 4b3b5881 60000000 <0fe00000> e8010090 7c0803a6 4bffff88 [ 2058.130240] ---[ end trace 0f471c192555a013 ]--- [ 2070.084234] kobject_test module unloaded Signed-off-by: Srikar Dronamraju <sri...@linux.vnet.ibm.com> --- lib/kobject.c | 22 +++++++++++++++++----- 1 file changed, 17 insertions(+), 5 deletions(-) diff --git a/lib/kobject.c b/lib/kobject.c index 389829d3a1d1..2d65be37fd7b 100644 --- a/lib/kobject.c +++ b/lib/kobject.c @@ -16,6 +16,7 @@ #include <linux/stat.h> #include <linux/slab.h> #include <linux/random.h> +#include <linux/uaccess.h> /** * kobject_namespace - return @kobj's namespace tag @@ -417,8 +418,11 @@ int kobject_add(struct kobject *kobj, struct kobject *parent, return -EINVAL; if (!kobj->state_initialized) { + char tmp; + int ret = probe_kernel_address(kobject_name(kobj), tmp); + pr_err("kobject '%s' (%p): tried to add an uninitialized object, something is seriously wrong.\n", - kobject_name(kobj), kobj); + ret ? " " : kobject_name(kobj), kobj); dump_stack(); return -EINVAL; } @@ -606,10 +610,14 @@ EXPORT_SYMBOL(kobject_del); struct kobject *kobject_get(struct kobject *kobj) { if (kobj) { - if (!kobj->state_initialized) + if (!kobj->state_initialized) { + char tmp; + int ret = probe_kernel_address(kobject_name(kobj), tmp); + WARN(1, KERN_WARNING "kobject: '%s' (%p): is not initialized, yet kobject_get() is being called.\n", - kobject_name(kobj), kobj); + ret ? " " : kobject_name(kobj), kobj); + } kref_get(&kobj->kref); } return kobj; @@ -701,10 +709,14 @@ static void kobject_release(struct kref *kref) void kobject_put(struct kobject *kobj) { if (kobj) { - if (!kobj->state_initialized) + if (!kobj->state_initialized) { + char tmp; + int ret = probe_kernel_address(kobject_name(kobj), tmp); + WARN(1, KERN_WARNING "kobject: '%s' (%p): is not initialized, yet kobject_put() is being called.\n", - kobject_name(kobj), kobj); + ret ? " " : kobject_name(kobj), kobj); + } kref_put(&kobj->kref, kobject_release); } } -- 2.17.1
