linux-kernel - Re: Boot warning at rcu_check_gp_start

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Message-Id: <D7FEEB19-B519-4AC6-ABA4-250200E2A4E9@lca.pw>
Date:   Tue, 21 Jan 2020 06:45:32 -0500
From:   Qian Cai <cai@....pw>
To:     paulmck@...nel.org
Cc:     rcu@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: Boot warning at rcu_check_gp_start_stall()



> On Jan 21, 2020, at 12:09 AM, Paul E. McKenney <paulmck@...nel.org> wrote:
> 
> This is what you get when a grace period has been requested, but does
> not start within 21 seconds or so.  The "->state: 0x1ffff" is a new one
> on me -- that normally happens only before RCU's grace-period kthread
> has been spawned.  But by 97 seconds after boot, it should definitely
> already be up and running.
> 
> Is the system responsive at this point?

Yes, it works fine.

> 
> Except...  Why is it taking 96 seconds for the system to get to the point
> where it prints "Dentry cache hash table entries:"?  That happens at 0.139
> seconds on my laptop.  And at about the same time on a much larger system.
> 
> I could easily imagine that all sorts of things would break when boot
> takes that long.

I suppose the kernel has CONFIG_EFI_PGT_DUMP=y, so it takes a while to run just before rcu_check_gp_start_stall().