[PATCH] random: Fix kernel panic due to system_wq use before init
From: Waiman Long
Date: Wed Sep 14 2016 - 15:04:03 EST
While booting a 4.8-rc6 kernel on a 16-socket 768-thread Broadwell-EX
system, the kernel panic'ed with the following log:
[ 51.837010] BUG: unable to handle kernel NULL pointer dereference at 0000000000000102
[ 51.845635] IP: [<ffffffff810a49d2>] __queue_work+0x32/0x420
[ 52.004366] Call Trace:
[ 52.007053] <IRQ>
[ 52.009171] [<ffffffff810a4de7>] queue_work_on+0x27/0x40
[ 52.015306] [<ffffffff8146ebd7>] credit_entropy_bits+0x1d7/0x2a0
[ 52.022002] [<ffffffff8146f339>] ? add_interrupt_randomness+0x1b9/0x210
[ 52.029366] [<ffffffff8146f339>] add_interrupt_randomness+0x1b9/0x210
[ 52.036544] [<ffffffff810ea670>] handle_irq_event_percpu+0x40/0x80
[ 52.043430] [<ffffffff810ea6eb>] handle_irq_event+0x3b/0x60
[ 52.049655] [<ffffffff810ede48>] handle_level_irq+0x88/0x100
[ 52.055968] [<ffffffff8103004b>] handle_irq+0xab/0x130
[ 52.061708] [<ffffffff81092861>] ? _local_bh_enable+0x21/0x50
[ 52.068125] [<ffffffff81037bf5>] ? __exit_idle+0x5/0x30
[ 52.073965] [<ffffffff816fc9ed>] do_IRQ+0x4d/0xd0
[ 52.079229] [<ffffffff816fa88c>] common_interrupt+0x8c/0x8c
[ 52.085444] <EOI>
[ 52.087568] [<ffffffff8106bea9>] ? try_to_free_pmd_page+0x9/0x40
[ 52.094462] [<ffffffff8106bea5>] ? try_to_free_pmd_page+0x5/0x40
[ 52.101157] [<ffffffff8106bf2a>] ? __unmap_pmd_range.part.5+0x4a/0x70
[ 52.108330] [<ffffffff8106c330>] unmap_pmd_range+0x130/0x250
[ 52.114644] [<ffffffff8106cb7b>] __cpa_process_fault+0x47b/0x5a0
[ 52.121339] [<ffffffff8106d7cb>] __change_page_attr+0x78b/0x9e0
[ 52.127946] [<ffffffff81065e45>] ? __raw_callee_save___native_queued_spin_unlock+0x15/0x30
[ 52.137124] [<ffffffff8106da98>] __change_page_attr_set_clr+0x78/0x300
[ 52.144404] [<ffffffff81229180>] ? __slab_alloc+0x4d/0x5c
[ 52.150436] [<ffffffff8106f15f>] kernel_map_pages_in_pgd+0x8f/0xd0
[ 52.157333] [<ffffffff81dc0fb0>] efi_setup_page_tables+0xcc/0x1d9
[ 52.164124] [<ffffffff81dc0a8d>] efi_enter_virtual_mode+0x35e/0x4af
[ 52.171117] [<ffffffff81d9e109>] start_kernel+0x41f/0x4c8
[ 52.177142] [<ffffffff81d9dad8>] ? set_init_arg+0x55/0x55
[ 52.183168] [<ffffffff81d9d120>] ? early_idt_handler_array+0x120/0x120
[ 52.190440] [<ffffffff81d9d5d6>] x86_64_start_reservations+0x2a/0x2c
[ 52.197516] [<ffffffff81d9d724>] x86_64_start_kernel+0x14c/0x16f
[ 52.204214] Code: 89 e5 41 57 41 56 49 89 f6 41 55 41 89 fd 41 54 49 89 d4 53 48 83 ec 10 89 7d d4 ff 14 25 a0 a7 c2 81 f6 c4 02 0f 85 0d 03 00 00 <41> f6 86 02 01 00 00 01 0f 85 ae 02 00 00 49 c7 c7 18 41 01 00
[ 52.225516] RIP [<ffffffff810a49d2>] __queue_work+0x32/0x420
[ 52.231838] RSP <ffff88bd7f403de8>
[ 52.235667] CR2: 0000000000000102
[ 52.239667] ---[ end trace 2ee7ea9d2908eb72 ]---
[ 52.244743] Kernel panic - not syncing: Fatal exception in interrupt
Looking at the panic'ed instruction indicated that system_wq was
used by credit_entropy_bits() before it it was initialized in an
early_initcall.
This patch prevents the schedule_work() call from being made before
system_wq is initialized.
Signed-off-by: Waiman Long <Waiman.Long@xxxxxxx>
---
drivers/char/random.c | 8 ++++++--
1 files changed, 6 insertions(+), 2 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 3efb3bf..3afc519 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -730,8 +730,12 @@ retry:
r->entropy_total >= 2*random_read_wakeup_bits) {
struct entropy_store *other = &blocking_pool;
- if (other->entropy_count <=
- 3 * other->poolinfo->poolfracbits / 4) {
+ /*
+ * We cannot call schedule_work() before system_wq
+ * is initialized.
+ */
+ if (system_wq && (other->entropy_count <=
+ 3 * other->poolinfo->poolfracbits / 4)) {
schedule_work(&other->push_work);
r->entropy_total = 0;
}
--
1.7.1