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Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1g7FAv-00039C-Sb; Tue, 02 Oct 2018 07:32:58 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 347CE20255986; Tue, 2 Oct 2018 09:32:54 +0200 (CEST) Date: Tue, 2 Oct 2018 09:32:54 +0200 From: Peter Zijlstra To: Rik van Riel Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, will.deacon@arm.com, songliubraving@fb.com, mingo@kernel.org, luto@kernel.org, hpa@zytor.com, npiggin@gmail.com, Linus Torvalds , Thomas Gleixner , efault@gmx.de Subject: Re: [PATCH 2/7] x86/mm/tlb: Restructure switch_mm_irqs_off() Message-ID: <20181002073254.GP3439@hirez.programming.kicks-ass.net> References: <20180926035844.1420-1-riel@surriel.com> <20180926035844.1420-3-riel@surriel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180926035844.1420-3-riel@surriel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 25, 2018 at 11:58:39PM -0400, Rik van Riel wrote: > Move some code that will be needed for the lazy -> !lazy state > transition when a lazy TLB CPU has gotten out of date. > > No functional changes, since the if (real_prev == next) branch > always returns. > > Suggested-by: Andy Lutomirski > Signed-off-by: Rik van Riel > Acked-by: Dave Hansen > Cc: Linus Torvalds > Cc: Peter Zijlstra > Cc: Thomas Gleixner > Cc: efault@gmx.de > Cc: kernel-team@fb.com > Link: http://lkml.kernel.org/r/20180716190337.26133-4-riel@surriel.com > Signed-off-by: Ingo Molnar > (cherry picked from commit 61d0beb5796ab11f7f3bf38cb2eccc6579aaa70b) > --- > arch/x86/mm/tlb.c | 64 ++++++++++++++++++++++++----------------------- > 1 file changed, 33 insertions(+), 31 deletions(-) > > diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c > index 54a5870190a6..1224f7fb1311 100644 > --- a/arch/x86/mm/tlb.c > +++ b/arch/x86/mm/tlb.c > @@ -187,6 +187,8 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, > u16 prev_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid); > unsigned cpu = smp_processor_id(); > u64 next_tlb_gen; > + bool need_flush; > + u16 new_asid; > > /* > * NB: The scheduler will call us with prev == next when switching > @@ -308,44 +310,44 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, > /* Let nmi_uaccess_okay() know that we're changing CR3. */ > this_cpu_write(cpu_tlbstate.loaded_mm, LOADED_MM_SWITCHING); > barrier(); > + } Compiling this gives me: CC arch/x86/mm/tlb.o ../arch/x86/mm/tlb.c: In function ‘switch_mm_irqs_off’: ../arch/x86/mm/tlb.c:315:5: warning: ‘need_flush’ may be used uninitialized in this function [-Wmaybe-uninitialized] if (need_flush) { ^ ../arch/x86/mm/tlb.c:316:45: warning: ‘new_asid’ may be used uninitialized in this function [-Wmaybe-uninitialized] this_cpu_write(cpu_tlbstate.ctxs[new_asid].ctx_id, next->context.ctx_id); ^ Because you shadow need_flush and new_asid in a branch. I need the below delta to make it happy again. --- --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -254,8 +254,6 @@ void switch_mm_irqs_off(struct mm_struct return; } else { - u16 new_asid; - bool need_flush; u64 last_ctx_id = this_cpu_read(cpu_tlbstate.last_ctx_id); /*