Greg, Linus, I'm not entirely clear on how acceptable it is to propose a different patch for -stable than what we have upstream.
The below Changelog explain, but in short, we should either backport 4 rather invasive patches to .13-stable and .14-stable or do the small patch provided. The 4 patches by Steven are the right thing to do, but I feel they might be too invasive to propose for -stable, therefore the alternative approach. --- Subject: x86,preempt: Fix preemption for i386 From: Peter Zijlstra <pet...@infradead.org> Date: Tue, 8 Apr 2014 14:21:28 +0200 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: fweis...@gmail.com Cc: mi...@kernel.org Cc: Steven Rostedt <rost...@goodmis.org> Cc: David Cohen <david.a.co...@linux.intel.com> Cc: Paolo Bonzini <pbonz...@redhat.com> Cc: Borislav Petkov <b...@alien8.de> Tested-by: Stefan Bader <stefan.ba...@canonical.com> Tested-by: Toralf Förster <toralf.foers...@gmx.de> Tested-by: Michele Ballabio <barra_c...@katamail.com> Signed-off-by: Peter Zijlstra <pet...@infradead.org> --- arch/x86/include/asm/preempt.h | 11 +++++++++++ include/linux/preempt.h | 4 ++++ include/linux/thread_info.h | 2 -- 3 files changed, 15 insertions(+), 2 deletions(-) --- a/arch/x86/include/asm/preempt.h +++ b/arch/x86/include/asm/preempt.h @@ -5,6 +5,17 @@ #include <asm/percpu.h> #include <linux/thread_info.h> +#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. + */ +#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 @@ -17,6 +17,10 @@ #include <asm/preempt.h> +#ifndef tif_need_resched +#define tif_need_resched() test_thread_flag(TIF_NEED_RESCHED) +#endif + #if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_PREEMPT_TRACER) extern void preempt_count_add(int val); extern void preempt_count_sub(int val); --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/