Re: [PATCH v3 4/8] lockdep: Add a kernel parameter, crossrelease_fullstack

Ingo Molnar
2017-10-24T10:12:40Z

* Byungchul Park <byungchul.park@lge.com> wrote:

> Make whether to allow recording full stack, in cross-release feature,
> switchable at boot time via a kernel parameter, 'crossrelease_fullstack'.
> In case of a splat with no stack trace, one could just reboot and set
> the kernel parameter to get the full data without having to recompile
> the kernel.
>
> Change CONFIG_CROSSRELEASE_STACK_TRACE default from N to Y, and
> introduce the new kernel parameter.
>
> Signed-off-by: Byungchul Park <byungchul.park@lge.com>
> ---
> Documentation/admin-guide/kernel-parameters.txt | 3 +++
> kernel/locking/lockdep.c | 18 ++++++++++++++++--
> lib/Kconfig.debug | 5 +++--
> 3 files changed, 22 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index ead7f40..4107b01 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -709,6 +709,9 @@
> It will be ignored when crashkernel=X,high is not used
> or memory reserved is below 4G.
>
> + crossrelease_fullstack
> + [KNL] Allow to record full stack trace in cross-release
> +
> cryptomgr.notests
> [KNL] Disable crypto self-tests
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 5c2ddf2..feba887 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -76,6 +76,15 @@
> #define lock_stat 0
> #endif
>
> +static int crossrelease_fullstack;
> +static int __init allow_crossrelease_fullstack(char *str)
> +{
> + crossrelease_fullstack = 1;
> + return 0;
> +}
> +
> +early_param("crossrelease_fullstack", allow_crossrelease_fullstack);
> +
> /*
> * lockdep_lock: protects the lockdep graph, the hashes and the
> * class/list/hash allocators.
> @@ -4864,8 +4873,13 @@ static void add_xhlock(struct held_lock *hlock)
> 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);
> + if (crossrelease_fullstack) {
> + xhlock->trace.skip = 3;
> + save_stack_trace(&xhlock->trace);
> + } else {
> + xhlock->trace.nr_entries = 1;
> + xhlock->trace.entries[0] = hlock->acquire_ip;
> + }
> #else
> xhlock->trace.nr_entries = 1;
> xhlock->trace.entries[0] = hlock->acquire_ip;
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index fe8fceb..132536d 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1228,7 +1228,7 @@ config LOCKDEP_COMPLETIONS
> config CROSSRELEASE_STACK_TRACE
> bool "Record more than one entity of stack trace in crossrelease"
> depends on LOCKDEP_CROSSRELEASE
> - default n
> + default y
> help
> The lockdep "cross-release" feature needs to record stack traces
> (of calling functions) for all acquisitions, for eventual later
> @@ -1238,7 +1238,8 @@ config CROSSRELEASE_STACK_TRACE
> full analysis. This option turns on the saving of the full stack
> trace entries.
>
> - If unsure, say N.
> + To make the feature actually on, set "crossrelease_fullstack"
> + kernel parameter, too.
>
> config DEBUG_LOCKDEP
> bool "Lock dependency engine debugging"

This is really unnecessarily complex.

The proper logic is to introduce the crossrelease_fullstack boot parameter, and to
also have a Kconfig option that enables it:

CONFIG_BOOTPARAM_LOCKDEP_CROSSRELEASE_FULLSTACK=y

No #ifdefs please - just an "if ()" branch dependent on the current value of
crossrelease_fullstack.

Thanks,

Ingo