Hi all, Luck, Tony wrote: >> So it's definitely in mainline, and its definitely >> not Seto-san's patch. > > Here's the root of the problem (arch/ia64/kernel/entry.S): > Please see: 841 GLOBAL_ENTRY(ia64_leave_kernel) 842 PT_REGS_UNWIND_INFO(0) 843 /* 844 * work.need_resched etc. mustn't get changed by this CPU before it returns to 845 * user- or fsys-mode, hence we disable interrupts early on. 846 * 847 * p6 controls whether current_thread_info()->flags needs to be check for 848 * extra work. We always check for extra work when returning to user-level. 849 * With CONFIG_PREEMPT, we also check for extra work when the preempt_count 850 * is 0. After extra work processing has been completed, execution 851 * resumes at .work_processed_syscall with p6 set to 1 if the extra-work-check 852 * needs to be redone. 853 */ 854 #ifdef CONFIG_PREEMPT 855 rsm psr.i // disable interrupts 856 cmp.eq p0,pLvSys=r0,r0 // pLvSys=0: leave from 856 kernel 857 (pKStk) adds r20=TI_PRE_COUNT+IA64_TASK_SIZE,r13 858 ;; 859 .pred.rel.mutex pUStk,pKStk 860 (pKStk) ld4 r21=[r20] // r21 <- preempt_count 861 (pUStk) mov r21=0 // r21 <- 0 862 ;; 863 cmp.eq p6,p0=r21,r0 // p6 <- pUStk || (preempt_count 863 == 0) 864 #else 865 (pUStk) rsm psr.i 866 cmp.eq p0,pLvSys=r0,r0 // pLvSys=0: leave from kernel 867 (pUStk) cmp.eq.unc p6,p0=r0,r0 // p6 <- pUStk 868 #endif 869 .work_processed_kernel: 870 adds r17=TI_FLAGS+IA64_TASK_SIZE,r13 871 ;; 872 (p6) ld4 r31=[r17] // load current_thread_i 872 nfo()->flags 873 adds r21=PT(PR)+16,r12 874 ;; 875 876 lfetch [r21],PT(CR_IPSR)-PT(PR) 877 adds r2=PT(B6)+16,r12 878 adds r3=PT(R16)+16,r12 879 ;; 880 lfetch [r21] 881 ld8 r28=[r2],8 // load b6 882 adds r29=PT(R24)+16,r12 883 884 ld8.fill r16=[r3],PT(AR_CSD)-PT(R16) 885 adds r30=PT(AR_CCV)+16,r12 886 (p6) and r19=TIF_WORK_MASK,r31 // any work other than T 886 IF_SYSCALL_TRACE? 887 ;; 888 ld8.fill r24=[r29] 889 ld8 r15=[r30] // load ar.ccv 890 (p6) cmp4.ne.unc p6,p0=r19, r0 // any special work pend 890 ing? 891 ;; 892 ld8 r29=[r2],16 // load b7 893 ld8 r30=[r3],16 // load ar.csd 894 (p6) br.cond.spnt .work_pending and: 1160 .work_pending_syscall: 1161 add r2=-8,r2 1162 add r3=-8,r3 1163 ;; 1164 st8 [r2]=r8 1165 st8 [r3]=r10 1166 .work_pending: 1167 tbit.z p6,p0=r31,TIF_NEED_RESCHED // current_thread_info()->need_resched==0? 1168 (p6) br.cond.sptk.few .notify 1169 #ifdef CONFIG_PREEMPT 1170 (pKStk) dep r21=-1,r0,PREEMPT_ACTIVE_BIT,1 1171 ;; 1172 (pKStk) st4 [r20]=r21 1173 ssm psr.i // enable interrupts 1174 #endif > 1175 br.call.spnt.many rp=schedule > 1176 .ret9: cmp.eq p6,p0=r0,r0 // p6 <- 1 > 1177 rsm psr.i // disable interrupts > 1178 ;; > 1179 #ifdef CONFIG_PREEMPT > 1180 (pKStk) adds r20=TI_PRE_COUNT+IA64_TASK_SIZE,r13 > 1181 ;; > 1182 (pKStk) st4 [r20]=r0 // preempt_count() <- 0 > 1183 #endif > 1184 (pLvSys)br.cond.sptk.few .work_pending_syscall_end > 1185 br.cond.sptk.many .work_processed_kernel // re-check > 1186 > 1187 .notify: > 1188 (pUStk) br.call.spnt.many rp=notify_resume_user > > on line 1188 we call notify_resume_user() with interrupts disabled (at > least if we fall through from the code above ... I didn't check the > state of interrupts if we branch to ".notify"). AFAIK, we always call notify_resume_user() with interrupts disabled. Is this right? > So we start down this call chain to the might_sleep() check: > > [<a000000100011bf0>] show_stack+0x50/0xa0 > [<a000000100011c70>] dump_stack+0x30/0x60 > [<a000000100061a90>] __might_sleep+0x1f0/0x220 > [<a000000100709020>] down_read+0x20/0x60 > [<a0000001000fe060>] access_process_vm+0x60/0x2c0 > [<a00000010002a280>] ia64_sync_kernel_rbs+0x40/0x100 > [<a00000010002a400>] do_sync_rbs+0xc0/0x100 > [<a00000010000ac30>] unw_init_running+0x70/0xa0 > [<a00000010002a5c0>] ia64_sync_krbs+0x80/0xa0 > [<a000000100012690>] do_notify_resume_user+0x110/0x140 > [<a00000010000aac0>] notify_resume_user+0x40/0x60 > [<a00000010000a9f0>] skip_rbs_switch+0xe0/0x110 > [<a000000000010740>] __kernel_syscall_via_break+0x0/0x20 So, I think the problem is not "why interrupts are disabled," but "why sleep in this path which always with interrupts disabled." It obviously means ia64_sync_kernel_rbs should care about that. The function was introduced by the following commit: > commit 3b2ce0b17824c42bc2e46f7dd903b4acf5e9fff9 > Author: Petr Tesarik <ptesarik@xxxxxxx> > Date: Wed Dec 12 15:23:34 2007 +0100 > > [IA64] Synchronize kernel RSE to user-space and back Hmm, could you make ia64_sync_kernel_rbs to safe with interrupts disabled, Petr? Thanks, H.Seto -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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