Commit b339a18b authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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.
parent f60f7008

arch/i386/kernel/process.c

+12 −8
Original line number Diff line number Diff line
@@ -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))

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