Messages in this thread |  | | Date | Wed, 16 Dec 2015 09:28:12 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH] ftrace: fix race between ftrace and insmod |
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On Wed, 16 Dec 2015 18:28:35 +0800 "Zhang, Yanmin" <yanmin_zhang@linux.intel.com> wrote:
> > + /* > > + * If the tracing is enabled, go ahead and enable the record. > > + * > > + * The reason not to enable the record immediatelly is the > > + * inherent check of ftrace_make_nop/ftrace_make_call for > > + * correct previous instructions. Making first the NOP > > + * conversion puts the module to the correct state, thus > > + * passing the ftrace_make_call check. > > + * > > + * We also delay this to after the module code already set the > > + * text to read-only, as we now need to set it back to read-write > > + * so that we can modify the text. > > + */ > > + if (ftrace_start_up) > > + ftrace_arch_code_modify_prepare(); > > + > > + do_for_each_ftrace_rec(pg, rec) { > > + int cnt; > > + /* > > + * do_for_each_ftrace_rec() is a double loop. > > + * module text shares the pg. If a record is > > + * not part of this module, then skip this pg, > > + * which the "break" will do. > > + */ > > + if (!within_module_core(rec->ip, mod)) > > + break; > > + > > + cnt = 0; > > + > > + /* > > + * When adding a module, we need to check if tracers are > > + * currently enabled and if they are, and can trace this record, > > + * we need to enable the module functions as well as update the > > + * reference counts for those function records. > > + */ > > + if (ftrace_start_up) > > + cnt += referenced_filters(rec); > > + > > + /* This clears FTRACE_FL_DISABLED */ > > + rec->flags = cnt; > > + > > + if (ftrace_start_up && cnt) { > > + int failed = __ftrace_replace_code(rec, 1); > > If we choose to call ftrace_module_enable when receiving module notification > MODULE_STATE_COMING, TEXT section of the module is already changed to RO.
And that's why we call ftrace_arch_code_modify_prepare(). That should change all text to RW.
-- Steve
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