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Date: Thu, 2 Feb 2023 17:02:07 +0100
From: Íñigo Huguet <ihuguet@...hat.com>
To: netdev@...r.kernel.org, richardcochran@...il.com,
yangbo.lu@....com, mlichvar@...hat.com,
gerhard@...leder-embedded.com
Cc: habetsm.xilinx@...il.com, ecree.xilinx@...il.com,
davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
pabeni@...hat.com, alex.maftei@....com
Subject: PTP vclock: BUG: scheduling while atomic
Hello,
Our QA team was testing PTP vclocks, and they've found this error with sfc NIC/driver:
BUG: scheduling while atomic: ptp5/25223/0x00000002
The reason seems to be that vclocks disable interrupts with `spin_lock_irqsave` in
`ptp_vclock_gettime`, and then read the timecounter, which in turns ends calling to
the driver's `gettime64` callback.
Vclock framework was added in commit 5d43f951b1ac ("ptp: add ptp virtual clock driver
framework").
At first glance, it seems that vclock framework is reusing the already existing callbacks
of the drivers' ptp clocks, but it's imposing a new limitation that didn't exist before:
now they can't sleep (due the spin_lock_irqsave). Sfc driver might sleep waiting for the
fw response.
Sfc driver can be fixed to avoid this issue, but I wonder if something might not be
correct in the vclock framework. I don't have enough knowledge about how clocks
synchronization should work regarding this, so I leave it to your consideration.
These are the logs with stack traces:
BUG: scheduling while atomic: ptp5/25223/0x00000002
[...skip...]
Call Trace:
dump_stack_lvl+0x34/0x48
__schedule_bug.cold+0x47/0x53
__schedule+0x40e/0x580
schedule+0x43/0xa0
schedule_timeout+0x88/0x160
? __bpf_trace_tick_stop+0x10/0x10
_efx_mcdi_rpc_finish+0x2a9/0x480 [sfc]
? efx_mcdi_send_request+0x1d5/0x260 [sfc]
? dequeue_task_stop+0x70/0x70
_efx_mcdi_rpc.constprop.0+0xcd/0x3d0 [sfc]
? update_load_avg+0x7e/0x730
_efx_mcdi_rpc_evb_retry+0x5d/0x1d0 [sfc]
efx_mcdi_rpc+0x10/0x20 [sfc]
efx_phc_gettime+0x5f/0xc0 [sfc]
ptp_vclock_read+0xa3/0xc0
timecounter_read+0x11/0x60
ptp_vclock_refresh+0x31/0x60
? ptp_clock_release+0x50/0x50
ptp_aux_kworker+0x19/0x40
kthread_worker_fn+0xa9/0x250
? kthread_should_park+0x30/0x30
kthread+0x146/0x170
? set_kthread_struct+0x50/0x50
ret_from_fork+0x1f/0x30
BUG: scheduling while atomic: ptp5/25223/0x00000000
[...skip...]
Call Trace:
dump_stack_lvl+0x34/0x48
__schedule_bug.cold+0x47/0x53
__schedule+0x40e/0x580
? ptp_clock_release+0x50/0x50
schedule+0x43/0xa0
kthread_worker_fn+0x128/0x250
? kthread_should_park+0x30/0x30
kthread+0x146/0x170
? set_kthread_struct+0x50/0x50
ret_from_fork+0x1f/0x30
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