Messages in this thread | | | Date | Tue, 1 Aug 2023 15:25:09 -0700 | Subject | Re: ARM board lockups/hangs triggered by locks and mutexes | From | Florian Fainelli <> |
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Hi Rafal,
On 8/1/23 15:10, Rafał Miłecki wrote: > Hi, > > Years ago I added support for Broadcom's BCM53573 SoCs. We released > firmwares based on Linux 4.4 (and later on 4.14) that worked almost > fine. There was one little issue we couldn't debug or fix: random hangs > and reboots. They were too rare to deal with (most devices worked fine > for weeks or months). > > Recently I updated my stable kernel 5.4 and I started experiencing > stability issues on my own! After some uptime (usually from 0 to 20 > minutes of close to zero activity) serial console hangs. I can't type > anything and I stop getting any messages. I've to wait about a minute > for watchdog to kick in and reboot device. > > ##### > > I took that great chance and decided to track the regression. > > Linux 5.4 stable branch worked stable up to the release v5.4.197. > Starting with v5.4.198 I started experiencing those stability issues. I > bisected it down to the commit 4460066eb248 ("ipv6: fix locking issues > with loops over idev->addr_list"): > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-5.4.y&id=4460066eb2480b9e203c73755e12e2efc820a27e > > With above commit reverted I was able to use stable 5.4 branch up to the > release v5.4.207. Starting with v5.4.208 it got unstable again. I > bisected it down to: > commit d0d583484d2e ("locking/refcount: Consolidate implementations of > refcount_t") > commit dab787c73f6e ("locking/refcount: Consolidate > REFCOUNT_{MAX,SATURATED} definitions") > commit 0d3182fbe689 ("locking/refcount: Move saturation warnings out of line") > commit 809554147d60 ("locking/refcount: Improve performance of generic > REFCOUNT_FULL code") > commit 9c9269977f03 ("locking/refcount: Move the bulk of the > REFCOUNT_FULL implementation into the <linux/refcount.h> header") > commit 04bff7d7b808 ("locking/refcount: Remove unused > refcount_*_checked() variants") > commit 513b19a43bec ("locking/refcount: Ensure integer operands are > treated as signed") > commit 68b4ee68e8c8 ("locking/refcount: Define constants for > saturation and max refcount values") > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-5.4.y&id=d0d583484d2ed9f5903edbbfa7e2a68f78b950b0 > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-5.4.y&id=dab787c73f6e38d8e7ed3c1e683385e8f0fe28a2 > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-5.4.y&id=0d3182fbe689e3808c03b6cde6be98237f9e0a4a > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-5.4.y&id=809554147d609163cfbaf815c443c575b538a7ef > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-5.4.y&id=9c9269977f03ab9c448c8b71581a951e0eb4fb7b > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-5.4.y&id=04bff7d7b8081c4bb2e8171be31d33df297eee5b > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-5.4.y&id=513b19a43becee5f7af6d283bb9d3d241a8a21a8 > https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-5.4.y&id=68b4ee68e8c8800cf8d6b61cc74b4031a0742a4c > (I didn't actually check above commits individually). > > Reverting above locking/refcount commits worked fine for few releases: > up to the v5.4.219. Starting with v5.4.220 I got hangs again. I bisected > that down to the commit 131287ff833d ("once: add DO_ONCE_SLOW() for > sleepable contexts"). > > Reverting that extra commit from v5.4.238 allows me to run Linux for > hours again (currently 3 devices x 6 hours and counting). So I need in > total 10+1 reverts from 5.4 branch to get a stable kernel. > > ##### > > I'm clueless at this point. Is that possible kernel has some locking bug > I can hit only using this specific SoC? BCM53573s have a single ARM > Cortex-A7 CPU running at 900 MHz. The only unusual thing about this hw I > can think of is a slow arch timer running at 36,8 kHz.
From the look of it, it seems like the CPU might have bugs with atomics?
Your log indicates that your Cortex-A7 is r0p5 which is described to be susceptible to ARM_ERRATA_814220, do you have it enabled by any chance, if not, can you enable it and see if makes any difference?
> > I tried compiling kernel with: > CONFIG_SOFTLOCKUP_DETECTOR=y > CONFIG_DETECT_HUNG_TASK=y > CONFIG_WQ_WATCHDOG=y > but it didn't change or report anything. > > Unfortunately enabling *any* of following options: > CONFIG_DEBUG_RT_MUTEXES=y > CONFIG_DEBUG_SPINLOCK=y > CONFIG_DEBUG_MUTEXES=y > seems to make locksup/hangs go away. I tried for few hours. > > Sadly I don't have access to JTAG or any low level debugging interface. > > Does looking at commits I reported above give anyone a hint on what may > be going on maybe? >
-- Florian
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