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
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