linux-kernel - Re: [PATCH 1/2] lockdep: Introduce CROSSRELEASE_STACK

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Date:   Wed, 18 Oct 2017 15:23:32 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Byungchul Park <byungchul.park@....com>
cc:     peterz@...radead.org, mingo@...nel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kernel-team@....com
Subject: Re: [PATCH 1/2] lockdep: Introduce CROSSRELEASE_STACK_TRACE and make
 it not unwind as default

On Wed, 18 Oct 2017, Byungchul Park wrote:
>  #ifdef CONFIG_LOCKDEP_CROSSRELEASE
> +#ifdef CONFIG_CROSSRELEASE_STACK_TRACE
>  #define MAX_XHLOCK_TRACE_ENTRIES 5
> +#else
> +#define MAX_XHLOCK_TRACE_ENTRIES 1
> +#endif
>  
>  /*
>   * This is for keeping locks waiting for commit so that true dependencies
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index e36e652..5c2ddf2 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -4863,8 +4863,13 @@ static void add_xhlock(struct held_lock *hlock)
>  	xhlock->trace.nr_entries = 0;
>  	xhlock->trace.max_entries = MAX_XHLOCK_TRACE_ENTRIES;
>  	xhlock->trace.entries = xhlock->trace_entries;
> +#ifdef CONFIG_CROSSRELEASE_STACK_TRACE
>  	xhlock->trace.skip = 3;
>  	save_stack_trace(&xhlock->trace);
> +#else
> +	xhlock->trace.nr_entries = 1;
> +	xhlock->trace.entries[0] = hlock->acquire_ip;
> +#endif

Hmm. Would it be possible to have this switchable at boot time via a
command line parameter? So in case of a splat with no stack trace, one
could just reboot and set something like 'lockdep_fullstack' on the kernel
command line to get the full data without having to recompile the kernel.

Thanks,

	tglx