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ftrace/x86: Add a comment to why we take text_mutex in ftrace_arch_code_modify_prepare()

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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>
This commit is contained in:
Steven Rostedt (VMware) 2019-06-27 21:18:19 -04:00
parent d5b844a2cf
commit 39611265ed
1 changed files with 5 additions and 0 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

5
arch/x86/kernel/ftrace.c
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@ -36,6 +36,11 @@
int ftrace_arch_code_modify_prepare(void)
{
/*
* Need to grab text_mutex to prevent a race from module loading
* and live kernel patching from changing the text permissions while
* ftrace has it set to "read/write".
*/
mutex_lock(&text_mutex);
set_kernel_text_rw();
set_all_modules_text_rw();