Re: [PATCH 3/4] sparc64: convert spinlock_t to raw_spinlock_t in mmu_context_t

[Kirill Tkhai <tkhai@yandex.ru>]

12.02.2014, 11:48, "Allen Pais" <allen.pais@oracle.com>:

>  On Wednesday 12 February 2014 02:43 AM, Kirill Tkhai wrote:
>>   06.01.2014, 07:56, "Allen Pais" <allen.pais@oracle.com>:
>>>   In the attempt of get PREEMPT_RT working on sparc64 using
>>>   linux-stable-rt version 3.10.22-rt19+, the kernel crash
>>>   with the following trace:
>>>
>>>   [ 1487.027884] I7: <rt_mutex_setprio+0x3c/0x2c0>
>>>   [ 1487.027885] Call Trace:
>>>   [ 1487.027887]  [00000000004967dc] rt_mutex_setprio+0x3c/0x2c0
>>>   [ 1487.027892]  [00000000004afe20] task_blocks_on_rt_mutex+0x180/0x200
>>>   [ 1487.027895]  [0000000000819114] rt_spin_lock_slowlock+0x94/0x300
>>>   [ 1487.027897]  [0000000000817ebc] __schedule+0x39c/0x53c
>>>   [ 1487.027899]  [00000000008185fc] schedule+0x1c/0xc0
>>>   [ 1487.027908]  [000000000048fff4] smpboot_thread_fn+0x154/0x2e0
>>>   [ 1487.027913]  [000000000048753c] kthread+0x7c/0xa0
>>>   [ 1487.027920]  [00000000004060c4] ret_from_syscall+0x1c/0x2c
>>>   [ 1487.027922]  [0000000000000000]           (null)
>  Now, consistently I've been getting sun4v_data_access_exception.
>  Here's the trace:
>  [ 4673.360121] sun4v_data_access_exception: ADDR[0000080000000000] CTX[0000] TYPE[0004], going.

I've never dived at sparc's tlb before, but it seems now I'm understanding.

arch_enter_lazy_mmu_mode() makes possible delayed tlb flushing. In !RT kernel
you collect flush requests before you really flush all of them.

In RT you collect them too, but you are able to be preempted in any moment.
So, you may switch to other process with unflushed tlb, which is very bad.

Try to not to set tb->active = 1; in arch_enter_lazy_mmu_mode(). Set it to zero.
We will look if this robust fix helps.


>  [ 4673.360124]               \|/ ____ \|/
>  [ 4673.360124]               "@'/ .. \`@"
>  [ 4673.360124]               /_| \__/ |_\
>  [ 4673.360124]                  \__U_/
>  [ 4673.360128] hackbench(4183): Dax [#1]
>  [ 4673.360137] CPU: 5 PID: 4183 Comm: hackbench Tainted: G        W    3.10.24-rt22+ #12
>  [ 4673.360141] task: fffff80f9c793840 ti: fffff80f9b270000 task.ti: fffff80f9b270000
>  [ 4673.360146] TSTATE: 0000004411e01606 TPC: 0000000000407b64 TNPC: 0000000000407b68 Y: 00000000    Tainted: G        W
>  [ 4673.360157] TPC: <tsb_flush+0x4/0x40>
>  [ 4673.360160] g0: fffff80f9c7c54b8 g1: 0000000000000001 g2: 0000000000008000 g3: 0000000000000000
>  [ 4673.360163] g4: fffff80f9c793840 g5: fffff80fcfc9c000 g6: fffff80f9b270000 g7: 0000000000000000
>  [ 4673.360167] o0: 0000080000000130 o1: 000003ffffe00400 o2: 0000000000878e48 o3: 0000000000000000
>  [ 4673.360170] o4: 0000000000000002 o5: 0000000000000000 sp: fffff80f9b272ec1 ret_pc: 00000000004520d0
>  [ 4673.360177] RPC: <flush_tsb_user+0x70/0x120>
>  [ 4673.360180] l0: 0000000000000001 l1: fffff80fd0800870 l2: 0000080000000000 l3: 00000000000001ff
>  [ 4673.360183] l4: fffff80f9852ea00 l5: fffff80f9852ee10 l6: 0000000000a87000 l7: 0000000000000000
>  [ 4673.360185] i0: fffff80fd0800868 i1: 0000000000000000 i2: 0000000000000000 i3: 0000000000000000
>  [ 4673.360187] i4: 0000000000000002 i5: 0000000000000030 i6: fffff80f9b272f71 i7: 00000000004515a8
>  [ 4673.360192] I7: <flush_tlb_pending+0x68/0xe0>
>  [ 4673.360193] Call Trace:
>  [ 4673.360198]  [00000000004515a8] flush_tlb_pending+0x68/0xe0
>  [ 4673.360203]  [000000000045185c] arch_leave_lazy_mmu_mode+0x3c/0x60
>  [ 4673.360210]  [000000000052e520] unmap_single_vma+0x400/0x6c0
>  [ 4673.360213]  [000000000052e808] unmap_vmas+0x28/0x60
>  [ 4673.360220]  [0000000000530cc8] exit_mmap+0x88/0x160
>  [ 4673.360226]  [000000000045e0d4] mmput+0x34/0xe0
>  [ 4673.360236]  [00000000004669fc] do_exit+0x1fc/0xa40
>  [ 4673.360241]  [0000000000467270] do_group_exit+0x30/0xe0
>  [ 4673.360245]  [000000000046733c] SyS_exit_group+0x1c/0x40
>  [ 4673.360256]  [0000000000406234] linux_sparc_syscall+0x34/0x44
>  [ 4673.360260] Caller[00000000004515a8]: flush_tlb_pending+0x68/0xe0
>  [ 4673.360264] Caller[000000000045185c]: arch_leave_lazy_mmu_mode+0x3c/0x60
>  [ 4673.360267] Caller[000000000052e520]: unmap_single_vma+0x400/0x6c0
>  [ 4673.360270] Caller[000000000052e808]: unmap_vmas+0x28/0x60
>  [ 4673.360274] Caller[0000000000530cc8]: exit_mmap+0x88/0x160
>  [ 4673.360277] Caller[000000000045e0d4]: mmput+0x34/0xe0
>  [ 4673.360280] Caller[00000000004669fc]: do_exit+0x1fc/0xa40
>  [ 4673.360284] Caller[0000000000467270]: do_group_exit+0x30/0xe0
>  [ 4673.360287] Caller[000000000046733c]: SyS_exit_group+0x1c/0x40
>  [ 4673.360291] Caller[0000000000406234]: linux_sparc_syscall+0x34/0x44
>
>  - Allen
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