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Date: Sun, 19 Feb 2012 11:46:36 -0800 (PST) From: Linus Torvalds <torvalds@...ux-foundation.org> To: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com> cc: x86@...nel.org, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: [PATCH] x86-32: don't switch to irq stack for a user-mode irq From: Linus Torvalds <torvalds@...ux-foundation.org> Date: Sun Feb 19 11:35:34 2012 -0800 x86-32: don't switch to irq stack for a user-mode irq If the irq happens in user mode, our kernel stack is empty (apart from the pt_regs themselves, of course), so there's no need or advantage to switch. And it really doesn't save any stack space, quite the reverse: it means that a nested interrupt cannot switch irq stacks. So instead of saving kernel stack space, it actually causes the potential for *more* stack usage. Also simplify the preemption count copy when we do switch stacks: just copy the whole preemption count, rather than just the softirq parts of it. There is no advantage to the partial copy: it is more effort to get a less correct result. Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org> --- This came up during the i387 work. It's not a bug, but I do believe that we do stupid things on x86-32 when we get an interrupt in user mode. I'm throwing this patch out here because I think it's the right thing to do, but I won't commit it myself or push it any more than this. arch/x86/kernel/irq_32.c | 11 +++-------- 1 files changed, 3 insertions(+), 8 deletions(-) diff --git a/arch/x86/kernel/irq_32.c b/arch/x86/kernel/irq_32.c index 40fc86161d92..58b7f27cb3e9 100644 --- a/arch/x86/kernel/irq_32.c +++ b/arch/x86/kernel/irq_32.c @@ -100,13 +100,8 @@ execute_on_irq_stack(int overflow, struct irq_desc *desc, int irq) irqctx->tinfo.task = curctx->tinfo.task; irqctx->tinfo.previous_esp = current_stack_pointer; - /* - * Copy the softirq bits in preempt_count so that the - * softirq checks work in the hardirq context. - */ - irqctx->tinfo.preempt_count = - (irqctx->tinfo.preempt_count & ~SOFTIRQ_MASK) | - (curctx->tinfo.preempt_count & SOFTIRQ_MASK); + /* Copy the preempt_count so that the [soft]irq checks work. */ + irqctx->tinfo.preempt_count = curctx->tinfo.preempt_count; if (unlikely(overflow)) call_on_stack(print_stack_overflow, isp); @@ -196,7 +191,7 @@ bool handle_irq(unsigned irq, struct pt_regs *regs) if (unlikely(!desc)) return false; - if (!execute_on_irq_stack(overflow, desc, irq)) { + if (user_mode_vm(regs) || !execute_on_irq_stack(overflow, desc, irq)) { if (unlikely(overflow)) print_stack_overflow(); desc->handle_irq(irq, desc); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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