Re: [lkp] [printk] 34578dc67f: EIP is at vprintk_emit+0x1ea/0x600

Sergey Senozhatsky
2016-02-24T01:18:26Z

Hello,

Cc Rob, Frank, Grant

On (02/24/16 00:53), Sergey Senozhatsky wrote:
[..]
> 284 [ 0.000000] per task-struct memory footprint: 2112 bytes
> 285 [ 0.000000] per task-struct memory footprint: 2112 bytes
> 286 [ 0.000000] ------------------------
> 287 [ 0.000000] ------------------------
> 288 [ 0.000000] | Locking API testsuite:
> 289 [ 0.000000] | Locking API testsuite:
> 290 [ 0.000000] ----------------------------------------------------------------------------
> 291 [ 0.000000] ----------------------------------------------------------------------------
> 292 [ 0.000000] | spin |wlock |rlock |mutex | wsem | rsem |
> 293 [ 0.000000] | spin |wlock |rlock |mutex | wsem | rsem |
> 294 [ 0.000000] --------------------------------------------------------------------------
> 295 [ 0.000000] --------------------------------------------------------------------------
>
>
> looking at your Kernel command line
>
> [ 0.000000] Kernel command line: root=/dev/ram0 user=lkp job=/lkp/scheduled/vm-kbuild-yocto-i386-53/bisect_boot-1-yocto-minimal-i386.cgz-i386-randconfig-h1-02192137-34578dc67f38c02ccbe696e4099967884caa8e15-20160220-72722-vao2m5-0.yaml ARCH=i386 kconfig=i386-randconfig-h1-02192137 branch=linux-next/master commi t=34578dc67f38c02ccbe696e4099967884caa8e15 BOOT_IMAGE=/pkg/linux/i386-randconfig-h1-02192137/gcc-5/34578dc67f38c02ccbe696e4099967884caa8e15/vmlinuz-4.5.0-rc4-00295-g34578dc max_uptime=600 RESULT_ROOT=/result/boot/1/vm-kbuild-yocto-i386/yocto-minimal-i386.cgz/i386-randconfig-h1-02192137/gcc-5/34578dc67f38c02ccbe69 6e4099967884caa8e15/9 LKP_SERVER=inn earlyprintk=ttyS0,115200 systemd.log_level=err debug apic=debug sysrq_always_enabled rcupdate.rcu_cpu_stall_timeout=100 panic=-1 softlockup_panic=1 nmi_watchdog=panic oops=panic load_ramdisk=2 prompt_ramdisk=0 console=ttyS0,115200 console=tty0 vga=normal rw ip=::::vm-kbuild-yo cto-i386-53::dhcp drbd.minor_count=8
>
>
> - earlyprintk=ttyS0,115200
> - console=ttyS0,115200
> - console=tty0
>
> and I see "bootconsole [earlyser0] enabled" but no "bootconsole [earlyser0] disabled" message, which
> I'd expect to see...
>

and you get the NMI watchdog softlockup because you have a whole bunch of

"of_overlay_destroy: Could not find overlay #6"
"### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6"

messages to print. seems that somehitng just pushes them in a loop.
there are too many of them:

** 16981217 printk messages dropped **
[ 33.495591] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
** 16981217 printk messages dropped **
[ 33.495591] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[ 33.495593] of_overlay_destroy: Could not find overlay #6
[ 33.495593] of_overlay_destroy: Could not find overlay #6

** 16981217 printk messages dropped **

[ 33.497583] of_overlay_destroy: Could not find overlay #6
[ 33.497583] of_overlay_destroy: Could not find overlay #6
[ 33.497584] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[ 33.497584] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[ 33.497586] of_overlay_destroy: Could not find overlay #6
[ 33.497586] of_overlay_destroy: Could not find overlay #6
[ 33.497587] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[ 33.497587] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[ 33.497589] of_overlay_destroy: Could not find overlay #6
[ 33.497589] of_overlay_destroy: Could not find overlay #6
[ 33.497589] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[ 33.497589] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[ 33.497591] of_overlay_destroy: Could not find overlay #6
[ 33.497591] of_overlay_destroy: Could not find overlay #6
[ 33.497592] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[ 33.497592] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[ 33.497594] of_overlay_destroy: Could not find overlay #6
[ 33.497594] of_overlay_destroy: Could not find overlay #6
[ 33.497595] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[ 33.497595] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[ 33.497596] of_overlay_destroy: Could not find overlay #6
[ 33.497596] of_overlay_destroy: Could not find overlay #6
[ 33.497597] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[ 33.497597] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[ 33.497599] of_overlay_destroy: Could not find overlay #6
[ 33.497599] of_overlay_destroy: Could not find overlay #6
[ 33.497600] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[ 33.497600] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[ 33.497601] of_overlay_destroy: Could not find overlay #6
[ 33.497601] of_overlay_destroy: Could not find overlay #6
[ 33.497602] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[ 33.497602] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[ 33.497604] of_overlay_destroy: Could not find overlay #6
[ 33.497604] of_overlay_destroy: Could not find overlay #6
[ 33.497605] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6
[ 33.497605] ### dt-test ### of_unittest_destroy_tracked_overlays: overlay destroy failed for #6

the source of "too many messages to printk" is this `while (1) loop'

static void of_unittest_destroy_tracked_overlays(void)
{
int id, ret, defers;

if (overlay_first_id < 0)
return;

/* try until no defers */
do {
defers = 0;
/* remove in reverse order */
for (id = MAX_UNITTEST_OVERLAYS - 1; id >= 0; id--) {
if (!(overlay_id_bits[BIT_WORD(id)] & BIT_MASK(id)))
continue;

ret = of_overlay_destroy(id + overlay_first_id);
if (ret != 0) {
defers++;
pr_warn("%s: overlay destroy failed for #%d\n",
__func__, id + overlay_first_id);
continue;
}

overlay_id_bits[BIT_WORD(id)] &= ~BIT_MASK(id);
}
} while (defers > 0);
}

I don't know what's the root cause of missing overlay id in idr,
but in this particular case the loop transform into /* well, "defers" should
overflow at some point, but I doubt we must count on it */

do {
ret = of_overlay_destroy()->idr_find()->pr_err("Could not find overlay"), return -ENODEV
if (ret != 0) {
pr_warn("overlay destroy failed for");
continue;
}

} while (1);

the "while (1) printk();" pattern is known to be dangerous; we need to
fix printk().

so something like this perhaps.

From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: [PATCH] fix endless loop

---
drivers/of/unittest.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
index 979b6e4..5058017 100644
--- a/drivers/of/unittest.c
+++ b/drivers/of/unittest.c
@@ -1165,6 +1165,12 @@ static void of_unittest_destroy_tracked_overlays(void)
continue;

ret = of_overlay_destroy(id + overlay_first_id);
+ if (ret == -ENODEV) {
+ pr_warn("%s: no overlay to destroy for #%d\n",
+ __func__, id + overlay_first_id);
+ continue;
+ }
+
if (ret != 0) {
defers++;
pr_warn("%s: overlay destroy failed for #%d\n",
--
2.7.1