linux-kernel - Re: [PATCH] lockdep: Introduce CONFIG_LOCKDEP

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Date:   Sat, 25 Jul 2020 06:48:21 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzbot <syzbot+62ebe501c1ce9a91f68c@...kaller.appspotmail.com>,
        syzbot <syzbot+91fd909b6e62ebe06131@...kaller.appspotmail.com>,
        syzbot <syzbot+cd0ec5211ac07c18c049@...kaller.appspotmail.com>
Subject: Re: [PATCH] lockdep: Introduce CONFIG_LOCKDEP_LARGE

On Sat, Jul 25, 2020 at 3:30 AM Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
>
> Since syzkaller continues various test cases until the kernel crashes,
> syzkaller tends to examine more locking dependencies than normal systems.
> As a result, syzbot is reporting that the fuzz testing was terminated
> due to hitting upper limits lockdep can track [1] [2] [3].
>
> Like CONFIG_LOCKDEP_SMALL which halves the upper limits, let's introduce
> CONFIG_LOCKDEP_LARGE which doubles the upper limits.
>
> [1] https://syzkaller.appspot.com/bug?id=3d97ba93fb3566000c1c59691ea427370d33ea1b
> [2] https://syzkaller.appspot.com/bug?id=381cb436fe60dc03d7fd2a092b46d7f09542a72a
> [3] https://syzkaller.appspot.com/bug?id=a588183ac34c1437fc0785e8f220e88282e5a29f
>
> Reported-by: syzbot <syzbot+cd0ec5211ac07c18c049@...kaller.appspotmail.com>
> Reported-by: syzbot <syzbot+91fd909b6e62ebe06131@...kaller.appspotmail.com>
> Reported-by: syzbot <syzbot+62ebe501c1ce9a91f68c@...kaller.appspotmail.com>
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> ---
>  kernel/locking/lockdep.c           | 4 ++++
>  kernel/locking/lockdep_internals.h | 5 +++++
>  lib/Kconfig.debug                  | 8 ++++++++
>  3 files changed, 17 insertions(+)
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 29a8de4..85ba7eb 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -1349,7 +1349,11 @@ static int add_lock_to_list(struct lock_class *this,
>  /*
>   * For good efficiency of modular, we use power of 2
>   */
> +#ifdef CONFIG_LOCKDEP_LARGE
> +#define MAX_CIRCULAR_QUEUE_SIZE                8192UL
> +#else
>  #define MAX_CIRCULAR_QUEUE_SIZE                4096UL

Maybe this number should be the config value? So that we don't ever
return here to introduce "VERY_LARGE" :)
Also somebody may use it to _reduce_ size of the table for a smaller kernel.

> +#endif
>  #define CQ_MASK                                (MAX_CIRCULAR_QUEUE_SIZE-1)
>
>  /*
> diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
> index baca699..00a3ec3 100644
> --- a/kernel/locking/lockdep_internals.h
> +++ b/kernel/locking/lockdep_internals.h
> @@ -93,6 +93,11 @@ enum {
>  #define MAX_LOCKDEP_CHAINS_BITS        15
>  #define MAX_STACK_TRACE_ENTRIES        262144UL
>  #define STACK_TRACE_HASH_SIZE  8192
> +#elif defined(CONFIG_LOCKDEP_LARGE)
> +#define MAX_LOCKDEP_ENTRIES    65536UL
> +#define MAX_LOCKDEP_CHAINS_BITS        17
> +#define MAX_STACK_TRACE_ENTRIES        1048576UL
> +#define STACK_TRACE_HASH_SIZE  32768
>  #else
>  #define MAX_LOCKDEP_ENTRIES    32768UL
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 9ad9210..69ba624 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1266,6 +1266,14 @@ config LOCKDEP
>  config LOCKDEP_SMALL
>         bool
>
> +config LOCKDEP_LARGE
> +       bool "Use larger buffer for tracking more locking dependencies"
> +       depends on LOCKDEP && !LOCKDEP_SMALL
> +       help
> +         If you say Y here, the upper limits the lock dependency engine uses will
> +         be doubled. Useful for fuzz testing which tends to test many complecated
> +         dependencies than normal systems.
> +
>  config DEBUG_LOCKDEP
>         bool "Lock dependency engine debugging"
>         depends on DEBUG_KERNEL && LOCKDEP
> --
> 1.8.3.1
>