On 04/18/17 18:31, Michael Ellerman wrote: > Frank Rowand <frowand.list@xxxxxxxxx> writes: > >> On 04/17/17 17:32, Tyrel Datwyler wrote: >>> This patch introduces event tracepoints for tracking a device_nodes >>> reference cycle as well as reconfig notifications generated in response >>> to node/property manipulations. >>> >>> With the recent upstreaming of the refcount API several device_node >>> underflows and leaks have come to my attention in the pseries (DLPAR) dynamic >>> logical partitioning code (ie. POWER speak for hotplugging virtual and physcial >>> resources at runtime such as cpus or IOAs). These tracepoints provide a >>> easy and quick mechanism for validating the reference counting of >>> device_nodes during their lifetime. >>> >>> Further, when pseries lpars are migrated to a different machine we >>> perform a live update of our device tree to bring it into alignment with the >>> configuration of the new machine. The of_reconfig_notify trace point >>> provides a mechanism that can be turned for debuging the device tree >>> modifications with out having to build a custom kernel to get at the >>> DEBUG code introduced by commit 00aa3720. >> >> I do not like changing individual (or small groups of) printk() style >> debugging information to tracepoint style. > > I'm not quite sure which printks() you're referring to. > > The only printks that are removed in this series are under #ifdef DEBUG, > and so are essentially not there unless you build a custom kernel. Yes, I am talking about pr_debug(), pr_info(), pr_err(), etc. > > They also only cover the reconfig case, which is actually less > interesting than the much more common and bug-prone get/put logic. When I was looking at the get/put issue I used pr_debug(). >> As far as I know, there is no easy way to combine trace data and printk() >> style data to create a single chronology of events. If some of the >> information needed to debug an issue is trace data and some is printk() >> style data then it becomes more difficult to understand the overall >> situation. > > If you enable CONFIG_PRINTK_TIME then you should be able to just sort > the trace and the printk output by the timestamp. If you're really > trying to correlate the two then you should probably just be using > trace_printk(). Except the existing debug code that uses pr_debug() does not use trace_printk(). And "just sort" does not apply to multi-line output like: cpuhp/23-147 [023] .... 128.324827: of_node_put: refcount=5, dn->full_name=/cpus/PowerPC,POWER8@10 cpuhp/23-147 [023] .... 128.324829: of_node_put: refcount=4, dn->full_name=/cpus/PowerPC,POWER8@10 cpuhp/23-147 [023] .... 128.324829: of_node_put: refcount=3, dn->full_name=/cpus/PowerPC,POWER8@10 cpuhp/23-147 [023] .... 128.324831: of_node_put: refcount=2, dn->full_name=/cpus/PowerPC,POWER8@10 drmgr-7284 [009] .... 128.439000: of_node_put: refcount=1, dn->full_name=/cpus/PowerPC,POWER8@10 drmgr-7284 [009] .... 128.439002: of_reconfig_notify: action=DETACH_NODE, dn->full_name=/cpus/PowerPC,POWER8@10, prop->name=null, old_prop->name=null drmgr-7284 [009] .... 128.439015: of_node_put: refcount=0, dn->full_name=/cpus/PowerPC,POWER8@10 drmgr-7284 [009] .... 128.439016: of_node_release: dn->full_name=/cpus/PowerPC,POWER8@10, dn->_flags=4 I was kinda hoping that maybe someone had already created a tool to deal with this issue. But not too optimistic. > But IMO this level of detail, tracing every get/put, does not belong in > printk. Trace points are absolutely the right solution for this type of > debugging. > > cheers > . > -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
