From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, Stefan Bader Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Steven Rostedt , David Cohen , Paolo Bonzini , Borislav Petkov , stable-commits@vger.kernel.org, Linus Torvalds , =?UTF-8?q?Toralf=20F=BFrster?= , Michele Ballabio , Peter Zijlstra , fweisbec@gmail.com, mingo@kernel.org, greg@kroah.com Subject: [PATCH 3.14 013/140] x86,preempt: Fix preemption for i386 Date: Wed, 28 May 2014 21:32:32 -0700 Message-Id: <20140529043051.100327598@linuxfoundation.org> In-Reply-To: <20140529043049.661315084@linuxfoundation.org> References: <20140529043049.661315084@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Peter Zijlstra Many people reported preemption/reschedule problems with i386 kernels for .13 and .14. After Michele bisected this to a combination of 3e8e42c69bb ("sched: Revert need_resched() to look at TIF_NEED_RESCHED") ded79754754 ("irq: Force hardirq exit's softirq processing on its own stack") it finally dawned on me that i386's current_thread_info() was to blame. When we are on interrupt/exception stacks, we fail to observe the right TIF_NEED_RESCHED bit and therefore the PREEMPT_NEED_RESCHED folding malfunctions. Current upstream fixes this by making i386 behave the same as x86_64 already did: 2432e1364bbe ("x86: Nuke the supervisor_stack field in i386 thread_info") b807902a88c4 ("x86: Nuke GET_THREAD_INFO_WITH_ESP() macro for i386") 0788aa6a23cb ("x86: Prepare removal of previous_esp from i386 thread_info structure") 198d208df437 ("x86: Keep thread_info on thread stack in x86_32") However, that is far too much to stuff into -stable. Therefore I propose we merge the below patch which uses task_thread_info(current) for tif_need_resched() instead of the ESP based current_thread_info(). This makes sure we always observe the one true TIF_NEED_RESCHED bit and things will work as expected again. Cc: bp@alien8.de Cc: fweisbec@gmail.com Cc: david.a.cohen@linux.intel.com Cc: mingo@kernel.org Cc: fweisbec@gmail.com Cc: greg@kroah.com Cc: Steven Rostedt Cc: gregkh@linuxfoundation.org Cc: pbonzini@redhat.com Cc: rostedt@goodmis.org Cc: stefan.bader@canonical.com Cc: mingo@kernel.org Cc: toralf.foerster@gmx.de Cc: David Cohen Cc: Steven Rostedt Cc: torvalds@linux-foundation.org Cc: Paolo Bonzini Cc: David Cohen Cc: Cc: Borislav Petkov Cc: Paolo Bonzini Cc: Cc: Borislav Petkov Cc: peterz@infradead.org Cc: Linus Torvalds Cc: barra_cuda@katamail.com Tested-by: Stefan Bader Tested-by: Toralf F�rster Tested-by: Michele Ballabio Signed-off-by: Greg Kroah-Hartman Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/20140409142447.GD13658@twins.programming.kicks-ass.net --- arch/x86/include/asm/preempt.h | 12 ++++++++++++ include/linux/preempt.h | 2 ++ include/linux/thread_info.h | 2 -- 3 files changed, 14 insertions(+), 2 deletions(-) --- a/arch/x86/include/asm/preempt.h +++ b/arch/x86/include/asm/preempt.h @@ -5,6 +5,18 @@ #include #include +#ifdef CONFIG_X86_32 +/* + * i386's current_thread_info() depends on ESP and for interrupt/exception + * stacks this doesn't yield the actual task thread_info. + * + * We hard rely on the fact that all the TIF_NEED_RESCHED bits are + * the same, therefore use the slightly more expensive version below. + */ +#undef tif_need_resched +#define tif_need_resched() test_tsk_thread_flag(current, TIF_NEED_RESCHED) +#endif + DECLARE_PER_CPU(int, __preempt_count); /* --- a/include/linux/preempt.h +++ b/include/linux/preempt.h @@ -15,6 +15,8 @@ */ #define PREEMPT_NEED_RESCHED 0x80000000 +#define tif_need_resched() test_thread_flag(TIF_NEED_RESCHED) + #include #if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_PREEMPT_TRACER) --- a/include/linux/thread_info.h +++ b/include/linux/thread_info.h @@ -118,8 +118,6 @@ static inline __deprecated void set_need */ } -#define tif_need_resched() test_thread_flag(TIF_NEED_RESCHED) - #if defined TIF_RESTORE_SIGMASK && !defined HAVE_SET_RESTORE_SIGMASK /* * An arch can define its own version of set_restore_sigmask() to get the