PM / devfreq: Synchronize devfreq_monitor_[start/stop]

In the Linux kernel, the following vulnerability has been resolved:

PM / devfreq: Synchronize devfreq_monitor_[start/stop]

There is a chance if a frequent switch of the governor

done in a loop result in timer list corruption where

timer cancel being done from two place one from

cancel_delayed_work_sync() and followed by expire_timers()

can be seen from the traces[1].

while true

do

echo "simple_ondemand" > /sys/class/devfreq/1d84000.ufshc/governor

echo "performance" > /sys/class/devfreq/1d84000.ufshc/governor

done

It looks to be issue with devfreq driver where

device_monitor_[start/stop] need to synchronized so that

delayed work should get corrupted while it is either

being queued or running or being cancelled.

Let's use polling flag and devfreq lock to synchronize the

queueing the timer instance twice and work data being

corrupted.

[1]

...

..

<idle>-0 [003] 9436.209662: timer_cancel timer=0xffffff80444f0428

<idle>-0 [003] 9436.209664: timer_expire_entry timer=0xffffff80444f0428 now=0x10022da1c function=__typeid__ZTSFvP10timer_listE_global_addr baseclk=0x10022da1c

<idle>-0 [003] 9436.209718: timer_expire_exit timer=0xffffff80444f0428

kworker/u16:6-14217 [003] 9436.209863: timer_start timer=0xffffff80444f0428 function=__typeid__ZTSFvP10timer_listE_global_addr expires=0x10022da2b now=0x10022da1c flags=182452227

vendor.xxxyyy.ha-1593 [004] 9436.209888: timer_cancel timer=0xffffff80444f0428

vendor.xxxyyy.ha-1593 [004] 9436.216390: timer_init timer=0xffffff80444f0428

vendor.xxxyyy.ha-1593 [004] 9436.216392: timer_start timer=0xffffff80444f0428 function=__typeid__ZTSFvP10timer_listE_global_addr expires=0x10022da2c now=0x10022da1d flags=186646532

vendor.xxxyyy.ha-1593 [005] 9436.220992: timer_cancel timer=0xffffff80444f0428

xxxyyyTraceManag-7795 [004] 9436.261641: timer_cancel timer=0xffffff80444f0428

[2]

9436.261653][ C4] Unable to handle kernel paging request at virtual address dead00000000012a

[ 9436.261664][ C4] Mem abort info:

[ 9436.261666][ C4] ESR = 0x96000044

[ 9436.261669][ C4] EC = 0x25: DABT (current EL), IL = 32 bits

[ 9436.261671][ C4] SET = 0, FnV = 0

[ 9436.261673][ C4] EA = 0, S1PTW = 0

[ 9436.261675][ C4] Data abort info:

[ 9436.261677][ C4] ISV = 0, ISS = 0x00000044

[ 9436.261680][ C4] CM = 0, WnR = 1

[ 9436.261682][ C4] [dead00000000012a] address between user and kernel address ranges

[ 9436.261685][ C4] Internal error: Oops: 96000044 [#1] PREEMPT SMP

[ 9436.261701][ C4] Skip md ftrace buffer dump for: 0x3a982d0

...

[ 9436.262138][ C4] CPU: 4 PID: 7795 Comm: TraceManag Tainted: G S W O 5.10.149-android12-9-o-g17f915d29d0c #1

[ 9436.262141][ C4] Hardware name: Qualcomm Technologies, Inc. (DT)

[ 9436.262144][ C4] pstate: 22400085 (nzCv daIf +PAN -UAO +TCO BTYPE=--)

[ 9436.262161][ C4] pc : expire_timers+0x9c/0x438

[ 9436.262164][ C4] lr : expire_timers+0x2a4/0x438

[ 9436.262168][ C4] sp : ffffffc010023dd0

[ 9436.262171][ C4] x29: ffffffc010023df0 x28: ffffffd0636fdc18

[ 9436.262178][ C4] x27: ffffffd063569dd0 x26: ffffffd063536008

[ 9436.262182][ C4] x25: 0000000000000001 x24: ffffff88f7c69280

[ 9436.262185][ C4] x23: 00000000000000e0 x22: dead000000000122

[ 9436.262188][ C4] x21: 000000010022da29 x20: ffffff8af72b4e80

[ 9436.262191][ C4] x19: ffffffc010023e50 x18: ffffffc010025038

[ 9436.262195][ C4] x17: 0000000000000240 x16: 0000000000000201

[ 9436.262199][ C4] x15: ffffffffffffffff x14: ffffff889f3c3100

[ 9436.262203][ C4] x13: ffffff889f3c3100 x12: 00000000049f56b8

[ 9436.262207][ C4] x11: 00000000049f56b8 x10: 00000000ffffffff

[ 9436.262212][ C4] x9 : ffffffc010023e50 x8 : dead000000000122

[ 9436.262216][ C4] x7 : ffffffffffffffff x6 : ffffffc0100239d8

[ 9436.262220][ C4] x5 : 0000000000000000 x4 : 0000000000000101

[ 9436.262223][ C4] x3 : 0000000000000080 x2 : ffffff8

---truncated---