Hi all,
I'm seeing the following warnings when I read from an IIO char device,
with CONFIG_DEBUG_ATOMIC_SLEEP=y. I'm testing a v4.4 kernel, but AFAICT,
nothing too relevant has changed between that and v4.7:
[ 10.831289] do not call blocking ops when !TASK_RUNNING; state=1 set at [<ffffffc00026b610>] prepare_to_wait_event+0xb0/0x11c
[ 10.845531] ------------[ cut here ]------------
[ 10.850161] WARNING: at kernel/sched/core.c:7630
[ 10.858672] Modules linked in: cfg80211 nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables asix usbnet mii joydev snd_seq_midi snd_seq_midi_event snd_rawmidi snd_seq snd_seq_device ppp_async ppp_generic slhc tun
[ 10.878459]
[ 10.879953] CPU: 4 PID: 1844 Comm: BrowserBlocking Not tainted 4.4.14 #190
[ 10.886817] Hardware name: Google Kevin (DT)
[ 10.891085] task: ffffffc0e5a88000 ti: ffffffc0e2ce4000 task.ti: ffffffc0e2ce4000
[ 10.898574] PC is at __might_sleep+0x64/0x90
[ 10.902846] LR is at __might_sleep+0x64/0x90
[ 10.907115] pc : [<ffffffc00024ed44>] lr : [<ffffffc00024ed44>] pstate: 60000145
[ 10.914500] sp : ffffffc0e2ce7ba0
[ 10.917813] x29: ffffffc0e2ce7ba0 x28: 0000000000000001
[ 10.923147] x27: 0000000000000000 x26: ffffffc0ed77b488
[ 10.928476] x25: ffffffc001082000 x24: 0000000000000000
[ 10.933809] x23: ffffffc0e2c49340 x22: 0000000000000000
[ 10.939139] x21: 0000000000000269 x20: ffffffc000c1314e
[ 10.944470] x19: ffffffc00114493e x18: 0000000000000000
[ 10.949798] x17: 0000000000000000 x16: ffffffc000372094
[ 10.955138] x15: 0000000000000000 x14: ffffffc0eacbb898
[ 10.960474] x13: ffffffc000c14919 x12: 0000000000000000
[ 10.965809] x11: 0000000000000000 x10: 0000000000001150
[ 10.971141] x9 : ffffffc0e2ce7920 x8 : ffffffc0e5a891b0
[ 10.976469] x7 : ffffffc000267934 x6 : ffffffc00024e7f0
[ 10.981805] x5 : 0000000000000000 x4 : 0000000000000001
[ 10.987138] x3 : 0000000000000000 x2 : cb88537fdc8ba60e
[ 10.992479] x1 : cb88537fdc8ba60e x0 : 0000000000000071
[ 10.997810]
...
[ 12.164333] ---[ end trace 45409966a9a76438 ]---
[ 12.168942] Call trace:
[ 12.171391] [<ffffffc00024ed44>] __might_sleep+0x64/0x90
[ 12.176699] [<ffffffc000954774>] mutex_lock_nested+0x50/0x3fc
[ 12.182440] [<ffffffc0007b9424>] iio_kfifo_buf_data_available+0x28/0x4c
[ 12.189043] [<ffffffc0007b76ac>] iio_buffer_ready+0x60/0xe0
[ 12.194608] [<ffffffc0007b7834>] iio_buffer_read_first_n_outer+0x108/0x1a8
[ 12.201474] [<ffffffc000370d48>] __vfs_read+0x58/0x114
[ 12.206606] [<ffffffc000371740>] vfs_read+0x94/0x118
[ 12.211564] [<ffffffc0003720f8>] SyS_read+0x64/0xb4
[ 12.216436] [<ffffffc000203cb4>] el0_svc_naked+0x24/0x28
Have any of you seen this kind of issue before (perhaps most IIO users
are not using CONFIG_DEBUG_ATOMIC_SLEEP)? If the WARNING is really
correct, then this problem has really been around a while. It looks like
we have a wait_event_interruptible() called, with this call chain in the
'condition' path:
iio_buffer_ready()
-> iio_buffer_data_available() (i.e., iio_kfifo_buf_data_available())
-> mutex_lock()
Calling mutex_lock() means we clobber the TASK_INTERRUPTIBLE state with
TASK_RUNNING -- hence, the WARNING. Should this be using a spinlock
instead? Or is there some way to refactor this to avoid calling these
sleeping functions in the wait_event*() condition?
Regards,
Brian
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