Public bug reported:
== Summary ==
A soft lockup (system freeze) occurs in the DPMAIF TX kernel thread
when system suspend (s2idle) is triggered while the thread is active.
== Environment ==
Kernel: 6.17.0-1017-oem (Ubuntu OEM)
Device: MediaTek MT6880 (FM350-GL) 0000:56:00.0
ASPM: L1 Enabled on endpoint (LnkCtl: ASPM L1 Enabled; ClockPM+)
Sleep: s2idle
== Reproduction ==
Trigger: SIM registered + ASPM L1 enabled + repeated suspend/resume
(hundreds of cycles)
Reproduction script (60s cycle):
while true; do
systemctl suspend
sleep 60
done
== Kernel Log ==
watchdog: BUG: soft lockup - CPU#10 stuck for 26s! [dpmaif_tx_hw_pu:625]
RIP: 0010:ktime_get_mono_fast_ns+0x67/0xd0
...
watchdog: BUG: soft lockup - CPU#10 stuck for 52s! [dpmaif_tx_hw_pu:625]
RIP: 0010:_raw_spin_unlock_irqrestore+0x3d/0x60
Call Trace:
__pm_runtime_resume+0x5b/0x80
t7xx_dpmaif_tx_hw_push_thread+0xc4/0x4e0 [mtk_t7xx]
== Root Cause ==
t7xx_dpmaif_suspend() stops the TX work queue via t7xx_dpmaif_tx_stop()
but does NOT signal the TX kthread or update dpmaif_ctrl->state.
The kthread can pass the state guard and call pm_runtime_resume_and_get()
concurrently with the system PM suspend path, causing a spinlock deadlock.
== Fix ==
See attached patch. Three changes:
1. t7xx_dpmaif_suspend(): set state=PWROFF + wake_up() to signal kthread
2. t7xx_dpmaif_resume(): restore state=PWRON (symmetric)
3. t7xx_dpmaif_tx_hw_push_thread(): add state guard before pm_runtime call
== Workaround ==
Disable ASPM L1 on endpoint:
LNKCTL=$(setpci -s 56:00.0 CAP_EXP+10.w)
setpci -s 56:00.0 CAP_EXP+10.w=$(printf "%04x" $((16#${LNKCTL} & ~0x2)))
(reduces probability but does not fully prevent the race)
== Testing ==
Patched module installed to /lib/modules/.../extra/mtk_t7xx.ko
Running suspend/resume loop with SIM registered — no lockup observed
(testing in progress, over 4000 cycles completed without regression).
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: kernel patch pcie regression wwan
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https://bugs.launchpad.net/bugs/2152281
Title:
net: wwan: t7xx: soft lockup in dpmaif_tx_hw_push_thread during
system suspend
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