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ftrace/x86: Add a comment to why we take text_mutex in ftrace_arch_code_modify_prepare()
Taking the text_mutex in ftrace_arch_code_modify_prepare() is to fix a race against module loading and live kernel patching that might try to change the text permissions while ftrace has it as read/write. This really needs to be documented in the code. Add a comment that does such. Link: http://lkml.kernel.org/r/20190627211819.5a591f52@gandalf.local.home Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com> Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com> Reviewed-by: Petr Mladek <pmladek@suse.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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@ -36,6 +36,11 @@
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int ftrace_arch_code_modify_prepare(void)
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{
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/*
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* Need to grab text_mutex to prevent a race from module loading
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* and live kernel patching from changing the text permissions while
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* ftrace has it set to "read/write".
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*/
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mutex_lock(&text_mutex);
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set_kernel_text_rw();
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set_all_modules_text_rw();
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