From bb5a93aaf25261321db0c499cde7da6ee9d8b164 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sun, 5 Jul 2020 12:50:20 -0700 Subject: [PATCH] x86/ldt: use "pr_info_once()" instead of open-coding it badly Using a mutex for "print this warning only once" is so overdesigned as to be actively offensive to my sensitive stomach. Just use "pr_info_once()" that already does this, although in a (harmlessly) racy manner that can in theory cause the message to be printed twice if more than one CPU races on that "is this the first time" test. [ If somebody really cares about that harmless data race (which sounds very unlikely indeed), that person can trivially fix printk_once() by using a simple atomic access, preferably with an optimistic non-atomic test first before even bothering to treat the pointless "make sure it is _really_ just once" case. A mutex is most definitely never the right primitive to use for something like this. ] Yes, this is a small and meaningless detail in a code path that hardly matters. But let's keep some code quality standards here, and not accept outrageously bad code. Link: https://lore.kernel.org/lkml/CAHk-=wgV9toS7GU3KmNpj8hCS9SeF+A0voHS8F275_mgLhL4Lw@mail.gmail.com/ Cc: Andy Lutomirski Cc: Thomas Gleixner Cc: Peter Zijlstra (Intel) Signed-off-by: Linus Torvalds --- arch/x86/kernel/ldt.c | 11 +---------- 1 file changed, 1 insertion(+), 10 deletions(-) diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c index 34e918a..b8aee71 100644 --- a/arch/x86/kernel/ldt.c +++ b/arch/x86/kernel/ldt.c @@ -559,16 +559,7 @@ static bool allow_16bit_segments(void) * is worthwhile, disallow 16-bit segments under Xen PV. */ if (xen_pv_domain()) { - static DEFINE_MUTEX(xen_warning); - static bool warned; - - mutex_lock(&xen_warning); - if (!warned) { - pr_info("Warning: 16-bit segments do not work correctly in a Xen PV guest\n"); - warned = true; - } - mutex_unlock(&xen_warning); - + pr_info_once("Warning: 16-bit segments do not work correctly in a Xen PV guest\n"); return false; } #endif -- 2.7.4