Hi,

On Sun, Jan 21, 2024 at 10:52:56PM +0100, Andrew Lunn wrote:

On Sun, Jan 21, 2024 at 09:17:32PM +0100, Marc Haber wrote:

quoted

Hi,

I am running a bunch of Banana Pis with Debian stable and unstable but
with a bleeding edge kernel. Since kernel 6.6, especially the test
system running Debian unstable is plagued by self-detected stalls on
CPU. The system seems to continue running normally locally but doesn't
answer on the network any more. Sometimes, after a few hours, things
heal themselves.

Here is an example log output:
[73929.363030] rcu: INFO: rcu_sched self-detected stall on CPU
[73929.368653] rcu:     1-....: (5249 ticks this GP) idle=d15c/1/0x40000002 softirq=471343/471343 fqs=2625
[73929.377796] rcu:     (t=5250 jiffies g=851349 q=113 ncpus=2)
[73929.383205] CPU: 1 PID: 14512 Comm: atop Tainted: G             L     6.6.0-zgbpi-armmp-lpae+ #1
[73929.383222] Hardware name: Allwinner sun7i (A20) Family
[73929.383233] PC is at stmmac_get_stats64+0x64/0x20c [stmmac]
[73929.383363] LR is at dev_get_stats+0x44/0x144
[73929.383389] pc : [<bf126db0>]    lr : [<c09525e8>]    psr: 200f0013
[73929.383401] sp : f0c59c78  ip : f0c59df8  fp : c2bb8000
[73929.383412] r10: 00800001  r9 : c3443dd8  r8 : 00000143
[73929.383423] r7 : 00000001  r6 : 00000000  r5 : c2bbb000  r4 : 00000001
[73929.383434] r3 : 0004c891  r2 : c2bbae48  r1 : f0c59d30  r0 : c2bb8000
[73929.383447] Flags: nzCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
[73929.383463] Control: 30c5387d  Table: 49b553c0  DAC: a7f66f60
[73929.383486]  stmmac_get_stats64 [stmmac] from dev_get_stats+0x44/0x144

Hi Marc

https://elixir.bootlin.com/linux/v6.7.1/source/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c#L6949

That is just for reference to the source? Or am I supposed to do
something with that link?

My _guess_ would be, its stuck in one of the loops which look like:

		do {
			start = u64_stats_fetch_begin(&txq_stats->syncp);
			tx_packets = txq_stats->tx_packets;
			tx_bytes   = txq_stats->tx_bytes;
		} while (u64_stats_fetch_retry(&txq_stats->syncp, start));

Next time you get a backtrace, could you do:

make drivers/net/ethernet/stmicro/stmmac/stmmac_main.lst. You can then
use whatever it is reporting for:

I have checked out 2eb85b750512cc5dc5a93d5ff00e1f83b99651db (which is
the first bad commit that the bisect eventually identified) and tried
running:

[56/4504]mh@fan:~/linux/git/linux ((2eb85b750512...)) $ make BUILDARCH="amd64" ARCH="arm" KBUILD_DEBARCH="armhf" CROSS_COMPILE="arm-linux-gnueabihf-" drivers/net/ethernet/stmicro/stmmac/stmmac_main.lst
  SYNC    include/config/auto.conf.cmd
  SYSHDR  arch/arm/include/generated/uapi/asm/unistd-oabi.h
  SYSHDR  arch/arm/include/generated/uapi/asm/unistd-eabi.h
  HOSTCC  scripts/kallsyms
  UPD     include/config/kernel.release
  UPD     include/generated/uapi/linux/version.h
  UPD     include/generated/utsrelease.h
  SYSNR   arch/arm/include/generated/asm/unistd-nr.h
  SYSTBL  arch/arm/include/generated/calls-oabi.S
  SYSTBL  arch/arm/include/generated/calls-eabi.S
  CC      scripts/mod/empty.o
  MKELF   scripts/mod/elfconfig.h
  HOSTCC  scripts/mod/modpost.o
  CC      scripts/mod/devicetable-offsets.s
  UPD     scripts/mod/devicetable-offsets.h
  HOSTCC  scripts/mod/file2alias.o
  HOSTCC  scripts/mod/sumversion.o
  HOSTLD  scripts/mod/modpost
  CC      kernel/bounds.s
  CC      arch/arm/kernel/asm-offsets.s
  UPD     include/generated/asm-offsets.h
  CALL    scripts/checksyscalls.sh
  CHKSHA1 include/linux/atomic/atomic-arch-fallback.h
  CHKSHA1 include/linux/atomic/atomic-instrumented.h
  MKLST   drivers/net/ethernet/stmicro/stmmac/stmmac_main.lst
./scripts/makelst: 1: arithmetic expression: expecting EOF: "0x - 0x00000000"
[57/4505]mh@fan:~/linux/git/linux ((2eb85b750512...)) $

That is not what it was suppsoed to yield, right?

PC is at stmmac_get_stats64+0x64/0x20c [stmmac]

to find where it is in the listing.

Once we know if its the RX or the TX loop, we have a better idea where
to look for an unbalanced u64_stats_update_begin() /
u64_stats_update_end().

quoted

I am running a bisect attempt since before christmas, but since it takes
up to a day for the issue to show themselves on a "bad" kernel, I'll let
"good" kernels run for four days until I declare them good. That takes a
lot of wall clock (or better, wall calendar) time.

You might be able to speed it up with:

while true ; do cat /proc/net/dev > /dev/null ; done

and iperf or similar to generate a lot of traffic.

My bisect eventually completed and identified
2eb85b750512cc5dc5a93d5ff00e1f83b99651db as the first bad commit.
Sadly, it doesnt contain any loops, no calls to u64_stats_update_begin()
or u64_stats_update_end() or other suspicious things to the casual
reader.

I have backed out that commit out of 6.7.1 and have booted that kernel.
Not long enough to be able to say something yet.

Greetings
Marc

-- 
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