On 5/3/19 10:47 AM, Evan Green wrote:
> Hey blockies,
^^^^^^^^^^^^
That's the weirdest greeting I have encountered so far on the
linux-block mailing list.
> I'm seeing a hung task in the kernel, and I wanted to share it in case
> it's a known issue. I'm still trying to wrap my head around the stacks
> myself. This is our Chrome OS 4.19 kernel, which is admittedly not
> 100% vanilla mainline master, but we try to keep it pretty close.
>
> I can reproduce this reliably within our chrome OS installer, where
> it's trying to dd from my system disk (NVMe) to a loop device backed
> by a removable UFS card (4kb sectors) in a USB dongle.
Although this is not the only possible cause such hangs are often caused
by a block driver or SCSI LLD not completing a request. A list of
pending requests can be obtained e.g. by running the attached script.
Bart.
#!/bin/bash
show_state() {
local a dev=$1
for a in device/state queue/scheduler; do
[ -e "$dev/$a" ] && grep -aH . "$dev/$a"
done
}
if [ -e /sys/kernel/debug/block ]; then
devs=($(cd /sys/kernel/debug/block && echo ./*))
else
devs=($(cd /sys/class/block && echo ./*))
fi
cd /sys/class/block || exit $?
for dev in "${devs[@]}"; do
dev="${dev#./}"
echo "$dev"
pending=0
if [ -e "$dev/mq" ]; then
for f in "$dev"/mq/*/{pending,*/rq_list}; do
[ -e "$f" ] || continue
if { read -r line1 && read -r line2; } <"$f"; then
echo "$f"
echo "$line1 $line2" >/dev/null
head -n 9 "$f"
((pending++))
fi
done
fi
(
busy=0
cd /sys/kernel/debug/block >&/dev/null &&
{ grep -aH . $dev/requeue_list; true; } &&
for d in "$dev"/mq/hctx* "$dev"/hctx*; do
[ ! -d "$d" ] && continue
{ [ ! -e "$d/tags" ] ||
grep -q '^busy=0$' "$d/tags"; } &&
{ [ ! -e "$d/sched_tags" ] ||
[ "$(<"$d/sched_tags")" = "" ] ||
grep -q '^busy=0$' "$d/sched_tags"; } && continue
((busy++))
for f in "$d"/{active,busy,dispatch,flags,requeue_list,sched_tags,state,tags*,cpu*/rq_list,sched/*rqs}; do
[ -e "$f" ] && grep -aH . "$f"
done
done
exit $busy
)
pending=$((pending+$?))
if [ "$pending" -gt 0 ]; then
(
cd /sys/kernel/debug/block >&/dev/null &&
if [ -e "$dev/mq/state" ]; then
grep -aH . "$dev/mq/state"
else
grep -aH . "$dev/state"
fi
)
show_state "$dev"
fi
done
