ARM Ftrace Function Graph Fails With UNWINDER_FRAME_POINTER

[Thorsten Scherer]

Hello,

in the context of a panic on an i.MX25 based v6.9 kernel [1] Uwe pointed me to
this thread.  With the proposed code change applied the procedure

    # set to some known good (randomly guessed) filter function and enable function_graph
    echo mtdblock_open > set_ftrace_filter
    echo function_graph > current_tracer

    # walk available filter funcs
    cat available_filter_functions | while read f; do echo $f | tee -a set_ftrace_filter; sleep 1; done

produces the following output

[  159.832173] Insufficient stack space to handle exception!
[  159.832241] Task stack:     [0xc8e44000..0xc8e46000]
[  159.842701] IRQ stack:      [0xc8800000..0xc8802000]
[  159.847712] Overflow stack: [0xc1934000..0xc1935000]
[  159.852726] Internal error: Oops - BUG: 0 [#1] PREEMPT ARM
[  159.858273] Modules linked in: capture_events_imxgpt ti_ads7950 industrialio_triggered_buffer kfifo_buf capture_events_irq capture_events iio_trig_hrtimer industrialio_sw_trigger industrialio_configfs dm_mod
[  159.876948] CPU: 0 PID: 199 Comm: sh Not tainted 6.9.0 #3
[  159.882412] Hardware name: Freescale i.MX25 (Device Tree Support)
[  159.888547] PC is at prepare_ftrace_return+0x4/0x7c
[  159.893520] LR is at ftrace_graph_caller+0x1c/0x28
[  159.898376] pc : [<c010dd44>]    lr : [<c010d988>]    psr: 60000093
[  159.904690] sp : c8e44018  ip : c8e44018  fp : c8e4403c
[  159.909959] r10: c0c09e78  r9 : c35e9bc0  r8 : c010d9bc
[  159.915227] r7 : 00000001  r6 : 00000004  r5 : c8e44064  r4 : c8e440ac
[  159.921800] r3 : c8e44030  r2 : c8e4403c  r1 : c010eb9c  r0 : c8e44038
[  159.928376] Flags: nZCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment none
[  159.935652] Control: 0005317f  Table: 83074000  DAC: 00000051
[  159.941436] Register r0 information: 2-page vmalloc region starting at 0xc8e44000 allocated at kernel_clone+0xa8/0x408
[  159.952253] Register r1 information: non-slab/vmalloc memory
[  159.957988] Register r2 information: 2-page vmalloc region starting at 0xc8e44000 allocated at kernel_clone+0xa8/0x408
[  159.968791] Register r3 information: 2-page vmalloc region starting at 0xc8e44000 allocated at kernel_clone+0xa8/0x408
[  159.979592] Register r4 information: 2-page vmalloc region starting at 0xc8e44000 allocated at kernel_clone+0xa8/0x408
[  159.990391] Register r5 information: 2-page vmalloc region starting at 0xc8e44000 allocated at kernel_clone+0xa8/0x408
[  160.001187] Register r6 information: non-paged memory
[  160.006303] Register r7 information: non-paged memory
[  160.011415] Register r8 information: non-slab/vmalloc memory
[  160.017139] Register r9 information: slab kmalloc-32 start c35e9bc0 pointer offset 0 size 32
[  160.025718] Register r10 information: non-slab/vmalloc memory
[  160.031530] Register r11 information: 2-page vmalloc region starting at 0xc8e44000 allocated at kernel_clone+0xa8/0x408
[  160.042422] Register r12 information: 2-page vmalloc region starting at 0xc8e44000 allocated at kernel_clone+0xa8/0x408
[  160.053315] Process sh (pid: 199, stack limit = 0x68fc3abb)
[  160.058955] Stack: (0xc8e44018 to 0xc8e46000)

and points me to copy_from_kernel_nofault_allowed.

    Disassembly of section .text:

    c010eb8c <copy_from_kernel_nofault_allowed>:
    c010eb8c:       e1a0c00d        mov     ip, sp
    c010eb90:       e92dd800        push    {fp, ip, lr, pc}
    c010eb94:       e24cb004        sub     fp, ip, #4
    c010eb98:       e52de004        push    {lr}            ; (str lr, [sp, #-4]!)
    c010eb9c:       ebfffb4f        bl      c010d8e0 <__gnu_mcount_nc>
    c010eba0:       e35004bf        cmp     r0, #-1090519040        ; 0xbf000000
    c010eba4:       3a000003        bcc     c010ebb8 <copy_from_kernel_nofault_allowed+0x2c>
    c010eba8:       e0900001        adds    r0, r0, r1
    c010ebac:       33a00001        movcc   r0, #1
    c010ebb0:       23a00000        movcs   r0, #0
    c010ebb4:       e89da800        ldm     sp, {fp, sp, pc}
    c010ebb8:       e3a00000        mov     r0, #0
    c010ebbc:       e89da800        ldm     sp, {fp, sp, pc}


In the time given I couldn't make sense of the issue, so I am passing this
hopefully useful information to you.

Best regards
Thorsten

#regzbot introduced: 953f534a7ed6b725d4f101d2949393acc9262880 ^

[1] https://lore.kernel.org/all/alp44tukzo6mvcwl4ke4ehhmojrqnv6xfcdeuliybxfjfvgd3e@gpjvwj33cc76/