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Date: Wed, 9 Oct 2013 16:17:37 +0200 From: Oleg Nesterov <oleg@...hat.com> To: Peter Zijlstra <peterz@...radead.org>, Richard Henderson <rth@...ddle.net>, Jakub Jelinek <jakub@...hat.com> Cc: Fengguang Wu <fengguang.wu@...el.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Ingo Molnar <mingo@...nel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [x86] BUG: unable to handle kernel paging request at 00740060 OK, thanks... I didn't notice Richard and Jakub were not cc'ed... Add them, perhaps they can take a look. On 10/09, Peter Zijlstra wrote: > > On Wed, Oct 09, 2013 at 02:43:10PM +0200, Oleg Nesterov wrote: > > I'm afraid I am wrong, my asm skills are close to zero... but this > > code looks wrong to me, and this can explain the oopses. > > > > > task_work_add: > > > pushl %ebp # > > > movl %esp, %ebp #, > > > pushl %edi # > > > pushl %esi # > > > pushl %ebx # > > > subl $12, %esp #, > > > call mcount > > > movl %eax, %edi # task, task > > > movl %edx, -16(%ebp) # work, %sfp > > > movb %cl, -21(%ebp) # notify, %sfp > > > .p2align 4,,15 > > > .L3: > > > movl 904(%edi), %esi # task_3(D)->task_works, head > > > cmpl $work_exited, %esi #, head > > > sete %bl #, D.14145 > > > andl $255, %ebx #, D.14145 > > > xorl %ecx, %ecx # > > > movl %ebx, %edx # D.14145, > > > movl $______f.14042, %eax #, > > > call ftrace_likely_update # > > > testl %ebx, %ebx # D.14145 > > > jne .L4 #, > > > movl -16(%ebp), %edx # %sfp, > > > movl %esi, (%edx) # head, work_13(D)->next > > > movl %esi, %eax # head, __ret > > > #APP > > > # 34 "/c/wfg/tip/kernel/task_work.c" 1 > > > cmpxchgl %edx,904(%edi) #, *__ptr_16 > > > # 0 "" 2 > > > #NO_APP > > > cmpl %eax, %esi # __ret, head > > > jne .L3 #, > > > > OK, we added the new work successfully, we should return 0. If we return > > non-zero, fput() (the likely caller) assumes that it should use the workqueues > > to close/free this file. Then later task_work_run() will do __fput() again. > > > > > cmpb $0, -21(%ebp) #, %sfp > > > je .L5 #, > > > movl 4(%edi), %eax # task_3(D)->stack, task_3(D)->stack > > > #APP > > > # 208 "/c/wfg/tip/arch/x86/include/asm/bitops.h" 1 > > > bts $1, 8(%eax); jc .L2 #, MEM[(volatile long unsigned int *)D.14203_29], > > > > This is set_notify_resume(). Probably !CONFIG_SMP (I do not see kick_process). > > > > > # 0 "" 2 > > > #NO_APP > > > .L5: > > > movl $0, -20(%ebp) #, %sfp > > > .L2: > > > movl -20(%ebp), %eax # %sfp, > > > > This is what we are going to return. But note that -20(%ebp) was not > > initialized if TIF_NOTIFY_RESUME was already set, "jc .L2" skips .L5 > > above. IOW, in this case we seem to return a random value from stack. > > I think you're quite right, and I can confirm I can reproduce this with > gcc-4.8.1 and Wu's .config: > > .p2align 4,,15 > .globl task_work_add > .type task_work_add, @function > task_work_add: > pushl %ebp # > movl %esp, %ebp #, > pushl %edi # > pushl %esi # > pushl %ebx # > subl $12, %esp #, > call mcount > movl %eax, %esi # task, task > movl %edx, %edi # work, work > movl %ecx, -24(%ebp) # notify, %sfp > jmp .L4 # > .p2align 4,,15 > .L9: > movl %ebx, (%edi) # __old, work_15(D)->next > movl %ebx, %eax # __old, __ret > #APP > # 34 "/usr/src/linux-2.6/kernel/task_work.c" 1 > cmpxchgl %edi,904(%esi) # work, *__ptr_17 > # 0 "" 2 > #NO_APP > cmpl %eax, %ebx # __ret, __old > je .L8 #, > .L4: > movl 904(%esi), %ebx # task_7(D)->task_works, __old > cmpl $work_exited, %ebx #, __old > sete -13(%ebp) #, %sfp > xorl %edx, %edx # ______r > movb -13(%ebp), %dl # %sfp, ______r > xorl %ecx, %ecx # > movl $______f.14204, %eax #, > call ftrace_likely_update # > cmpb $0, -13(%ebp) #, %sfp > je .L9 #, > movl $-3, -20(%ebp) #, %sfp > .L2: > movl -20(%ebp), %eax # %sfp, > addl $12, %esp #, > popl %ebx # > popl %esi # > popl %edi # > popl %ebp # > ret > .p2align 4,,15 > .L8: > cmpb $0, -24(%ebp) #, %sfp > je .L6 #, > movl 4(%esi), %eax # task_7(D)->stack, task_7(D)->stack > #APP > # 208 "/usr/src/linux-2.6/arch/x86/include/asm/bitops.h" 1 > bts $1, 8(%eax); jc .L2 #, MEM[(volatile long unsigned int *)_23], > # 0 "" 2 > #NO_APP > .L6: > movl $0, -20(%ebp) #, %sfp > movl -20(%ebp), %eax # %sfp, > addl $12, %esp #, > popl %ebx # > popl %esi # > popl %edi # > popl %ebp # > ret > .size task_work_add, .-task_work_add > > Once I force a x86_64 build using the 'same' config it goes away and > generates 'sensible' code again (although I don't see why L9 isn't > merged with L2): > > .p2align 4,,15 > .globl task_work_add > .type task_work_add, @function > task_work_add: > call __fentry__ > pushq %rbp # > movq %rsp, %rbp #, > pushq %r15 # > pushq %r14 # > movl %edx, %r14d # notify, notify > pushq %r13 # > movq %rsi, %r13 # work, work > pushq %r12 # > movq %rdi, %r12 # task, task > pushq %rbx # > jmp .L4 # > .p2align 4,,10 > .p2align 3 > .L11: > movq %rbx, 0(%r13) # __old, work_17(D)->next > movq %rbx, %rax # __old, __ret > #APP > # 34 "/usr/src/linux-2.6/kernel/task_work.c" 1 > cmpxchgq %r13,1312(%r12) # work, *__ptr_19 > # 0 "" 2 > #NO_APP > cmpq %rax, %rbx # __ret, __old > je .L10 #, > .L4: > movq 1312(%r12), %rbx # task_7(D)->task_works, __old > movq $______f.14855, %rdi #, > cmpq $work_exited, %rbx #, __old > sete %r15b #, tmp72 > xorl %edx, %edx # > movzbl %r15b, %esi # tmp72, ______r > call ftrace_likely_update # > testb %r15b, %r15b # tmp72 > je .L11 #, > movl $-3, %eax #, D.15034 > .L2: > popq %rbx # > popq %r12 # > popq %r13 # > popq %r14 # > popq %r15 # > popq %rbp # > ret > .p2align 4,,10 > .p2align 3 > .L10: > xorl %eax, %eax # D.15034 > testb %r14b, %r14b # notify > je .L2 #, > movq 8(%r12), %rdx # task_7(D)->stack, task_7(D)->stack > #APP > # 208 "/usr/src/linux-2.6/arch/x86/include/asm/bitops.h" 1 > bts $1, 16(%rdx); jc .L9 #, MEM[(volatile long unsigned int *)_25], > # 0 "" 2 > #NO_APP > .L9: > popq %rbx # > popq %r12 # > popq %r13 # > popq %r14 # > popq %r15 # > popq %rbp # > ret > .size task_work_add, .-task_work_add > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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