Messages in this thread | | | Date | Thu, 17 Dec 2015 14:48:52 +0800 | From | "Zhang, Yanmin" <> | Subject | Re: [PATCH] ftrace: fix race between ftrace and insmod |
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On 2015/12/16 22:28, Steven Rostedt wrote: > 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.
Thanks for the kind pointer. We would add codes into your patch based on notifier and send patch to you by private email.
Yanmin
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