From: Boqun Feng <boqun.feng@gmail.com>
To: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Cc: dsterba@suse.cz, Btrfs BTRFS <linux-btrfs@vger.kernel.org>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
Chris Murphy <lists@colorremedies.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
Waiman Long <longman@redhat.com>,
Joel Fernandes <joel@joelfernandes.org>
Subject: Re: BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
Date: Thu, 26 Jan 2023 15:49:33 -0800 [thread overview]
Message-ID: <Y9MRjd0cZgSNVzi6@boqun-archlinux> (raw)
In-Reply-To: <CABXGCsMD6nAPpF34c6oMK47kHUQqADQPUCWrxyY7WFiKi1qPNg@mail.gmail.com>
On Fri, Jan 27, 2023 at 03:42:52AM +0500, Mikhail Gavrilov wrote:
> On Thu, Jan 26, 2023 at 10:39 PM Boqun Feng <boqun.feng@gmail.com> wrote:
> >
> > [Cc lock folks]
> >
> > On Thu, Jan 26, 2023 at 02:47:42PM +0500, Mikhail Gavrilov wrote:
> > > On Wed, Jan 25, 2023 at 10:21 PM David Sterba <dsterba@suse.cz> wrote:
> > > >
> > > > On Wed, Jan 25, 2023 at 01:27:48AM +0500, Mikhail Gavrilov wrote:
> > > > > On Tue, Jul 26, 2022 at 9:47 PM David Sterba <dsterba@suse.cz> wrote:
> > > > > >
> > > > > > On Tue, Jul 26, 2022 at 05:32:54PM +0500, Mikhail Gavrilov wrote:
> > > > > > > Hi guys.
> > > > > > > Always with intensive writing on a btrfs volume, the message "BUG:
> > > > > > > MAX_LOCKDEP_CHAIN_HLOCKS too low!" appears in the kernel logs.
> > > > > >
> > > > > > Increase the config value of LOCKDEP_CHAINS_BITS, default is 16, 18
> > > > > > tends to work.
> > > > >
> > > > > Hi,
> > > > > Today I was able to get the message "BUG: MAX_LOCKDEP_CHAIN_HLOCKS too
> > > > > low!" again even with LOCKDEP_CHAINS_BITS=18 and kernel 6.2-rc5.
> > > > >
> > > > > ❯ cat /boot/config-`uname -r` | grep LOCKDEP_CHAINS_BITS
> > > > > CONFIG_LOCKDEP_CHAINS_BITS=18
> > > > >
> > > > > [88685.088099] BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
> > > > > [88685.088124] turning off the locking correctness validator.
> > > > > [88685.088133] Please attach the output of /proc/lock_stat to the bug report
> > > > > [88685.088142] CPU: 14 PID: 1749746 Comm: mv Tainted: G W L
> > > > > ------- --- 6.2.0-0.rc5.20230123git2475bf0250de.38.fc38.x86_64 #1
> > > > > [88685.088154] Hardware name: System manufacturer System Product
> > > > > Name/ROG STRIX X570-I GAMING, BIOS 4408 10/28/2022
> > > > >
> > > > > What's next? Increase this value to 19?
> > > >
> > > > Yes, though increasing the value is a workaround so you may see the
> > > > warning again.
> > >
> > > Is there any sense in this WARNING if we would ignore it and every
> > > time increase the threshold value?
> >
> > Lockdep uses static allocated array to track lock holdings chains to
> > avoid dynmaic memory allocation in its own code. So if you see the
> > warning it means your test has more combination of lock holdings than
> > the array can record. In other words, you reach the resource limitation,
> > and in that sense it makes sense to just ignore it and increase the
> > value: you want to give lockdep enough resource to work, right?
>
> It is needed for correct working btrfs. David, am I right?
>
Lockdep is not needed for correct working btrfs in production. It's a
tool to help btrfs developers to find deadlocks in
development/test/debug environment. End users, i.e. the users of linux
kernel don't need it.
Regards,
Boqun
> >
> > > May Be set 99 right away? Or remove such a check condition?
> >
> > That requires having 2^99 * 5 * sizeof(u16) memory for lock holding
> > chains array..
> >
> > However, a few other options we can try in lockdep are:
> >
> > * warn but not turn off the lockdep: the lock holding chain is
> > only a cache for what lock holding combination lockdep has ever
> > see, we also record the dependency in the graph. Without the
> > lock holding chain, lockdep can still work but just slower.
> >
> > * allow dynmaic memory allocation in lockdep: I think this might
> > be OK since we have lockdep_recursion to avoid lockdep code ->
> > mm code -> lockdep code -> mm code ... deadlock. But maybe I'm
> > missing something. And even we allow it, the use of memory
> > doesn't change, you will still need that amout of memory to
> > track lock holding chains.
> >
> > I'm not sure whether these options are better than just increasing the
> > number, maybe to unblock your ASAP, you can try make it 30 and make sure
> > you have large enough memory to test.
>
> About just to increase the LOCKDEP_CHAINS_BITS by 1. Where should this
> be done? In vanilla kernel on kernel.org? In a specific distribution?
> or the user must rebuild the kernel himself? Maybe increase
> LOCKDEP_CHAINS_BITS by 1 is most reliable solution, but it difficult
> to distribute to end users because the meaning of using packaged
> distributions is lost (user should change LOCKDEP_CHAINS_BITS in
> config and rebuild the kernel by yourself).
>
> It would be great if the chosen value would simply work always
> everywhere. 30? ok! But as I understand, btrfs does not have any
> guarantees for this. David, am I right?
>
> Anyway, thank you for keeping the conversation going.
>
> --
> Best Regards,
> Mike Gavrilov.
next prev parent reply other threads:[~2023-01-26 23:50 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-26 12:32 BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low! Mikhail Gavrilov
2022-07-26 16:42 ` David Sterba
2022-07-26 19:19 ` Chris Murphy
2022-07-26 19:21 ` Chris Murphy
2022-07-26 20:42 ` David Sterba
2022-08-03 19:28 ` Mikhail Gavrilov
2022-08-03 20:00 ` Chris Murphy
2022-08-04 7:35 ` Mikhail Gavrilov
2022-08-04 11:23 ` Tetsuo Handa
2023-01-24 20:27 ` Mikhail Gavrilov
2023-01-25 17:15 ` David Sterba
2023-01-26 9:47 ` Mikhail Gavrilov
2023-01-26 17:38 ` Boqun Feng
2023-01-26 18:30 ` Waiman Long
2023-01-26 18:59 ` Boqun Feng
2023-01-26 19:07 ` Waiman Long
2023-01-26 22:42 ` Mikhail Gavrilov
2023-01-26 22:51 ` Boqun Feng
2023-01-26 23:49 ` Boqun Feng [this message]
2023-01-27 0:20 ` Waiman Long
2023-01-27 3:37 ` Chris Murphy
2023-01-27 4:07 ` Boqun Feng
2023-01-27 5:35 ` Mikhail Gavrilov
2023-01-27 14:26 ` Waiman Long
2023-01-27 15:33 ` Chris Murphy
-- strict thread matches above, loose matches on Subject: below --
2020-12-09 8:02 Dmitry Vyukov
2019-03-06 18:04 syzbot
2019-04-11 1:43 ` syzbot
2019-04-11 12:14 ` syzbot
2019-04-11 21:50 ` Benjamin Herrenschmidt
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