Date:   Thu, 16 Mar 2023 08:54:50 +0100
From:   Andrea Righi <andrea.righi@canonical.com>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     Ard Biesheuvel <ardb@kernel.org>,
        Paolo Pisati <paolo.pisati@canonical.com>,
        linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: kernel 6.2 stuck at boot (efi_call_rts) on arm64
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Hello,

the latest v6.2.6 kernel fails to boot on some arm64 systems, the kernel
gets stuck and never completes the boot. On the console I see this:

[   72.043484] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
[   72.049571] rcu:     22-...0: (30 GPs behind) idle=b10c/1/0x4000000000000000 softirq=164/164 fqs=6443
[   72.058520]     (detected by 28, t=15005 jiffies, g=449, q=174 ncpus=32)
[   72.064949] Task dump for CPU 22:
[   72.068251] task:kworker/u64:5   state:R  running task     stack:0     pid:447   ppid:2      flags:0x0000000a
[   72.078156] Workqueue: efi_rts_wq efi_call_rts
[   72.082595] Call trace:
[   72.085029]  __switch_to+0xbc/0x100
[   72.088508]  0xffff80000fe83d4c

After that, as a consequence, I start to get a lot of hung task timeout traces.

I tried to bisect the problem and I found that the offending commit is
this one:

 e7b813b32a42 ("efi: random: refresh non-volatile random seed when RNG is initialized")

I've reverted this commit for now and everything works just fine, but I
was wondering if the problem could be caused by a lack of entropy on
these arm64 boxes or something else.

Any suggestion? Let me know if you want me to do any specific test.

Thanks,
-Andrea