From b339a18b81a1f6ca1455559594f5df872b9e59f4 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Fri, 22 Jul 2005 15:23:47 -0400 Subject: [PATCH] Fix up incorrect "unlikely()" on %gs reload in x86 __switch_to These days %gs is normally the TLS segment, so it's no longer zero. As a result, we shouldn't just assume that %fs/%gs tend to be zero together, but test them independently instead. Also, fix setting of debug registers to use the "next" pointer instead of "current". It so happens that the scheduler will have set the new current pointer before calling __switch_to(), but that's just an implementation detail. --- arch/i386/kernel/process.c | 20 ++++++++++++-------- 1 file changed, 12 insertions(+), 8 deletions(-) diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c index ba243a4..d949205 100644 --- a/arch/i386/kernel/process.c +++ b/arch/i386/kernel/process.c @@ -700,23 +700,27 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas /* * Restore %fs and %gs if needed. + * + * Glibc normally makes %fs be zero, and %gs is one of + * the TLS segments. */ - if (unlikely(prev->fs | prev->gs | next->fs | next->gs)) { + if (unlikely(prev->fs | next->fs)) loadsegment(fs, next->fs); + + if (prev->gs | next->gs) loadsegment(gs, next->gs); - } /* * Now maybe reload the debug registers */ if (unlikely(next->debugreg[7])) { - set_debugreg(current->thread.debugreg[0], 0); - set_debugreg(current->thread.debugreg[1], 1); - set_debugreg(current->thread.debugreg[2], 2); - set_debugreg(current->thread.debugreg[3], 3); + set_debugreg(next->debugreg[0], 0); + set_debugreg(next->debugreg[1], 1); + set_debugreg(next->debugreg[2], 2); + set_debugreg(next->debugreg[3], 3); /* no 4 and 5 */ - set_debugreg(current->thread.debugreg[6], 6); - set_debugreg(current->thread.debugreg[7], 7); + set_debugreg(next->debugreg[6], 6); + set_debugreg(next->debugreg[7], 7); } if (unlikely(prev->io_bitmap_ptr || next->io_bitmap_ptr)) -- 2.7.4