Reminder: 5 open syzbot bugs in lockdep subsystem

Reminder: 5 open syzbot bugs in lockdep subsystem

[Eric Biggers]

[This email was generated by a script.  Let me know if you have any suggestions
to make it better, or if you want it re-generated with the latest status.]

Of the currently open syzbot reports against the upstream kernel, I've manually
marked 5 of them as possibly being bugs in the lockdep subsystem.  I've listed
these reports below, sorted by an algorithm that tries to list first the reports
most likely to be still valid, important, and actionable.

Of these 5 bugs, 3 were seen in mainline in the last week.

Of these 5 bugs, 1 was bisected to a commit from the following person:

	Bart Van Assche <bvanassche@acm.org>

If you believe a bug is no longer valid, please close the syzbot report by
sending a '#syz fix', '#syz dup', or '#syz invalid' command in reply to the
original thread, as explained at https://goo.gl/tpsmEJ#status

If you believe I misattributed a bug to the lockdep subsystem, please let me
know, and if possible forward the report to the correct people or mailing list.

Here are the bugs:

--------------------------------------------------------------------------------
Title:              BUG: MAX_STACK_TRACE_ENTRIES too low! (2)
Last occurred:      0 days ago
Reported:           102 days ago
Branches:           Mainline and others
Dashboard link:     https://syzkaller.appspot.com/bug?id=55fb46b50c9b08dfe294667f184db5840f9cdecc
Original thread:    https://lkml.kernel.org/lkml/0000000000005ff8b20585395280@google.com/T/#u

This bug has a C reproducer.

This bug was bisected to:

	commit 669de8bda87b92ab9a2fc663b3f5743c2ad1ae9f
	Author: Bart Van Assche <bvanassche@acm.org>
	Date:   Thu Feb 14 23:00:54 2019 +0000

	  kernel/workqueue: Use dynamic lockdep keys for workqueues

The original thread for this bug received 2 replies; the last was 0 hours ago.

If you fix this bug, please add the following tag to the commit:
    Reported-by: syzbot+6f39a9deb697359fe520@syzkaller.appspotmail.com

If you send any email or patch for this bug, please reply to the original
thread, which had activity only 0 hours ago.  For the git send-email command to
use, or tips on how to reply if the thread isn't in your mailbox, see the "Reply
instructions" at https://lkml.kernel.org/r/0000000000005ff8b20585395280@google.com

--------------------------------------------------------------------------------
Title:              BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
Last occurred:      0 days ago
Reported:           125 days ago
Branches:           Mainline and others
Dashboard link:     https://syzkaller.appspot.com/bug?id=381cb436fe60dc03d7fd2a092b46d7f09542a72a
Original thread:    https://lkml.kernel.org/lkml/000000000000b7fd51058370d0d9@google.com/T/#u

This bug has a C reproducer.

syzbot has bisected this bug, but I think the bisection result is incorrect.

The original thread for this bug received 1 reply, 89 days ago.

If you fix this bug, please add the following tag to the commit:
    Reported-by: syzbot+91fd909b6e62ebe06131@syzkaller.appspotmail.com

If you send any email or patch for this bug, please consider replying to the
original thread.  For the git send-email command to use, or tips on how to reply
if the thread isn't in your mailbox, see the "Reply instructions" at
https://lkml.kernel.org/r/000000000000b7fd51058370d0d9@google.com

--------------------------------------------------------------------------------
Title:              BUG: MAX_LOCKDEP_CHAINS too low!
Last occurred:      5 days ago
Reported:           284 days ago
Branches:           Mainline and others
Dashboard link:     https://syzkaller.appspot.com/bug?id=bf037f4725d40a8d350b2b1b3b3e0947c6efae85
Original thread:    https://lkml.kernel.org/lkml/0000000000007523a60576e80a47@google.com/T/#u

Unfortunately, this bug does not have a reproducer.

The original thread for this bug received 3 replies; the last was 284 days ago.

If you fix this bug, please add the following tag to the commit:
    Reported-by: syzbot+aaa6fa4949cc5d9b7b25@syzkaller.appspotmail.com

If you send any email or patch for this bug, please consider replying to the
original thread.  For the git send-email command to use, or tips on how to reply
if the thread isn't in your mailbox, see the "Reply instructions" at
https://lkml.kernel.org/r/0000000000007523a60576e80a47@google.com

--------------------------------------------------------------------------------
Title:              BUG: MAX_LOCK_DEPTH too low! (2)
Last occurred:      362 days ago
Reported:           392 days ago
Branches:           Mainline and others
Dashboard link:     https://syzkaller.appspot.com/bug?id=e4feb2f88affd6242e3153d5c14ebb8569b499b8
Original thread:    https://lkml.kernel.org/lkml/000000000000798298056e76cbbb@google.com/T/#u

This bug has a C reproducer.

No one replied to the original thread for this bug.

If you fix this bug, please add the following tag to the commit:
    Reported-by: syzbot+802a5abb8abae86eb6de@syzkaller.appspotmail.com

If you send any email or patch for this bug, please consider replying to the
original thread.  For the git send-email command to use, or tips on how to reply
if the thread isn't in your mailbox, see the "Reply instructions" at
https://lkml.kernel.org/r/000000000000798298056e76cbbb@google.com

--------------------------------------------------------------------------------
Title:              BUG: MAX_LOCKDEP_ENTRIES too low!
Last occurred:      23 days ago
Reported:           22 days ago
Branches:           linux-next
Dashboard link:     https://syzkaller.appspot.com/bug?id=3d97ba93fb3566000c1c59691ea427370d33ea1b
Original thread:    https://lkml.kernel.org/lkml/000000000000ec7273058b877e1f@google.com/T/#u

Unfortunately, this bug does not have a reproducer.

No one has replied to the original thread for this bug yet.

If you fix this bug, please add the following tag to the commit:
    Reported-by: syzbot+cd0ec5211ac07c18c049@syzkaller.appspotmail.com

If you send any email or patch for this bug, please consider replying to the
original thread.  For the git send-email command to use, or tips on how to reply
if the thread isn't in your mailbox, see the "Reply instructions" at
https://lkml.kernel.org/r/000000000000ec7273058b877e1f@google.com

Re: Reminder: 5 open syzbot bugs in lockdep subsystem

[Bart Van Assche]

On 7/9/19 10:58 PM, Eric Biggers wrote:
> [This email was generated by a script.  Let me know if you have any suggestions
> to make it better, or if you want it re-generated with the latest status.]
> 
> Of the currently open syzbot reports against the upstream kernel, I've manually
> marked 5 of them as possibly being bugs in the lockdep subsystem.  I've listed
> these reports below, sorted by an algorithm that tries to list first the reports
> most likely to be still valid, important, and actionable.
> 
> Of these 5 bugs, 3 were seen in mainline in the last week.
> 
> Of these 5 bugs, 1 was bisected to a commit from the following person:
> 
> 	Bart Van Assche <bvanassche@acm.org>

(+jeffv)

Hi Eric,

Several days ago I had already explained to you that the bisection 
result that led to one of my commits did not make any sense to me. So I 
do not appreciate this kind of fingerpointing. Please stop doing this.

Bart.

Re: Reminder: 5 open syzbot bugs in lockdep subsystem

[Eric Biggers]

Hi Bart,

On Wed, Jul 10, 2019 at 07:14:10AM -0700, Bart Van Assche wrote:
> On 7/9/19 10:58 PM, Eric Biggers wrote:
> > [This email was generated by a script.  Let me know if you have any suggestions
> > to make it better, or if you want it re-generated with the latest status.]
> > 
> > Of the currently open syzbot reports against the upstream kernel, I've manually
> > marked 5 of them as possibly being bugs in the lockdep subsystem.  I've listed
> > these reports below, sorted by an algorithm that tries to list first the reports
> > most likely to be still valid, important, and actionable.
> > 
> > Of these 5 bugs, 3 were seen in mainline in the last week.
> > 
> > Of these 5 bugs, 1 was bisected to a commit from the following person:
> > 
> > 	Bart Van Assche <bvanassche@acm.org>
> 
> (+jeffv)
> 
> Hi Eric,
> 
> Several days ago I had already explained to you that the bisection result
> that led to one of my commits did not make any sense to me. So I do not
> appreciate this kind of fingerpointing. Please stop doing this.
> 
> Bart.
> 

To be clear, the email you sent saying the bisection was messed up was 3 months
ago (not "several days ago") , and was on the list, not to me personally:
https://lore.kernel.org/lkml/f71aaffa-ecf4-1def-fe50-91f37c677537@acm.org/
And at the time you didn't give any reason why your commit can't be responsible.

I then responded yesterday and explained why another crash showed up at the end
of the bisection log, and why I think the bisection result is actually correct
(https://lore.kernel.org/lkml/20190710053030.GB2152@sol.localdomain/).  BTW, I
even took the time to manually verify that the issue is not present in the
commit immediately before your commit, and that it appears when just
"kernel/workqueue: Use dynamic lockdep keys for workqueues" and
"locking/lockdep: Shrink struct lock_class_key" are applied (the latter is
needed to fix a WARNING the reproducer also causes).

I then sent out this reminder to group together the syzbot reports where the
lockdep limits are reached, in the hope that they would be related, and helpful
to you and the lockdep maintainers.  Since one bug had a bisection result that I
had manually reviewed and believed to be accurate, my reminder mentions that
result for that bug, just like I've been doing when I've been sending out syzbot
reminders for other subsystems.

I disagree that I should stop including bisection results (namely, the ones that
I've manually reviewed and believed to be accurate; the raw results reported by
syzbot are not too accurate, so I haven't been including them without review) in
reminders because it's "finger pointing".  They can be very helpful for fixing
bugs and getting the right people to work on them.  In fact, people often refuse
to fix syzbot bugs that do not have bisection results, because they expect a
bisection result before they bother to take a look at it.

Anyway, this bug is still there in mainline Linux, regardless of whose fault it
is.  None of this changes the fact that someone needs to fix it.  I'll look into
it more if I have time, though this very much seems to be in lockdep territory,
and there are 500 other syzbot bugs that need to be worked on too.

- Eric