On 05/25/2006 07:56 AM, Ruediger Pluem wrote: > During my analysis of PR39643 > (http://issues.apache.org/bugzilla/show_bug.cgi?id=39643) > I found out that mod_cache and mod_filter do not work together correctly. In > fact mod_filter > crashes with a segfault if the content is delivered from the cache. > > The segfault is caused by line 366 of mod_filter (filter_harness): > > if (!ctx->func) { > > filter_harness implements the output filter of mod_filter. > It expects that its context has been initialized and does not perform a check > if this is true. > > Why is the context not initialized, if we deliver content from the cache? > > This is because the filters (and thus the contexts of at least some filters) > get initialized > in ap_invoke_filter_init which is a static function in config.c. > ap_invoke_filter_init gets > only called by ap_invoke_handler (also in config.c). But if we deliver > content from the cache we > do this inside the quick handler hook, which is run *before* > ap_invoke_handler. Although we call > ap_run_insert_filter in the mod_cache quick handler we do *not* initialize > the filters there. > > So basicly I see the following approach for a fix: > > 1. In mod_filter do a sanity check if the filter context has been > initialized. If not remove ourselves > from the chain and simply pass the brigade. This could be done by the > following simple patch: > > --- mod_filter.c (Revision 408729) > +++ mod_filter.c (Arbeitskopie) > @@ -355,7 +355,7 @@ > harness_ctx *ctx = f->ctx; > ap_filter_rec_t *filter = f->frec; > > - if (f->r->status != 200) { > + if ((!ctx) || (f->r->status != 200)) { > ap_remove_output_filter(f); > return ap_pass_brigade(f->next, bb); > } > > Or does somebody sees a need for an error message here if the context is > not initialized? > > 2. Convert ap_invoke_filter_init from a static function to a public function > that is part of the API > and let mod_cache call it after ap_run_insert_filter. > Questions: > > 1. What kind of DECLARE macro should be used to convert it to a public > function ? > 2. To which header file should we add the prototype? > 3. Any special steps needed to adjust exports.c or is this done > automatically during > make / configure? > 4. Does this require a minor bump (I assume yes)? > > Comments / Thoughts / Answers ?
Ping. Any further comments? Especially any answers to my questions? With answers to my questions I would be able to prepare a patch for further discussion :-). Regards Rüdiger
