On Mon, 2015-03-02 at 11:37 -0500, Steven Rostedt wrote: > On Mon, 2 Mar 2015 10:01:00 -0600 > Tom Zanussi <tom.zanu...@linux.intel.com> wrote: > > > Add a gfp flag that allows kmalloc() et al to be used in tracing > > functions. > > > > The problem with using kmalloc for tracing is that the tracing > > subsystem should be able to trace kmalloc itself, which it can't do > > directly because of paths like kmalloc()->trace_kmalloc()->kmalloc() > > or kmalloc()->trace_mm_page_alloc()->kmalloc(). > > This part I don't like at all. Why can't the memory be preallocated > when the hist is created (the echo 'hist:...')? >
Yeah, I didn't like it either. My original version did exactly what you suggest and preallocated an array of entries to 'allocate' from in order to avoid the problem. But I wanted to attempt to use the bpf_map directly, which already uses kmalloc internally. My fallback in case this wouldn't fly, which it obviously won't, would be to add an option to have the bpf_map code preallocate a maximum number of entries or pass in a client-owned array for the purpose. I'll do that if I don't hear any better ideas.. Tom > kmalloc must never be called from any tracepoint callback. > > This change is currently a showstopper. > > -- Steve > > > > > > With this flag, tracing code could use a special version of kmalloc() > > that sets __GFP_NOTRACE on every allocation it does, while leaving the > > normal kmalloc() path untouched. > > > > This would allow any tracepoint in the kmalloc path to be avoided via > > DEFINE_EVENT_CONDITION() redefinitions of those events, which check > > for ___GFP_NOTRACE immediately in their execution and break if set, > > thereby avoiding the recursion. > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/