Re: Page fault in midi/sequencer.c

On Sun, Oct 21, 2018 at 12:59 AM Peter Holm <peter_at_holm.cc> wrote:

> I can trigger this on 13.0-CURRENT r339445 with a non-root test program:
>
> Calling uiomove() with the following non-sleepable locks held:
> exclusive sleep mutex seqflq (seqflq) r = 0 (0xfffff80003860c08) locked _at_
> dev/sound/midi/sequencer.c:952
> stack backtrace:
> #0 0xffffffff80bfe263 at witness_debugger+0x73
> #1 0xffffffff80bff1b8 at witness_warn+0x448
> #2 0xffffffff80bf6a91 at uiomove_faultflag+0x71
> #3 0xffffffff809439e6 at mseq_write+0x4c6
> #4 0xffffffff80a4f725 at devfs_write_f+0x185
> #5 0xffffffff80c02a87 at dofilewrite+0x97
> #6 0xffffffff80c0287f at kern_pwritev+0x5f
> #7 0xffffffff80c0277d at sys_pwrite+0x8d
> #8 0xffffffff81070af7 at amd64_syscall+0x2a7
> #9 0xffffffff8104a4ad at fast_syscall_common+0x101
> Kernel page fault with the following non-sleepable locks held:
> exclusive sleep mutex seqflq (seqflq) r = 0 (0xfffff80003860c08) locked _at_
> dev/sound/midi/sequencer.c:952
> stack backtrace:
> #0 0xffffffff80bfe263 at witness_debugger+0x73
> #1 0xffffffff80bff1b8 at witness_warn+0x448
> #2 0xffffffff810700d3 at trap_pfault+0x53
> #3 0xffffffff8106f70a at trap+0x2ba
> #4 0xffffffff81049bc5 at calltrap+0x8
> #5 0xffffffff80bf6b42 at uiomove_faultflag+0x122
> #6 0xffffffff809439e6 at mseq_write+0x4c6
> #7 0xffffffff80a4f725 at devfs_write_f+0x185
> #8 0xffffffff80c02a87 at dofilewrite+0x97
> #9 0xffffffff80c0287f at kern_pwritev+0x5f
> #10 0xffffffff80c0277d at sys_pwrite+0x8d
> #11 0xffffffff81070af7 at amd64_syscall+0x2a7
> #12 0xffffffff8104a4ad at fast_syscall_common+0x101
>
>
> Fatal trap 12: page fault while in kernel mode
> cpuid = 4; apic id = 04
> fault virtual address = 0x20ea6b
> fault code  = supervisor read data, page not present
> instruction pointer = 0x20:0xffffffff8106d32d
> stack pointer         = 0x28:0xfffffe00a844a660
> frame pointer         = 0x28:0xfffffe00a844a660
> code segment  = base 0x0, limit 0xfffff, type 0x1b
>    = DPL 0, pres 1, long 1, def32 0, gran 1
> processor eflags = interrupt enabled, resume, IOPL = 0
> current process  = 2356 (xxx)
> [ thread pid 2356 tid 100278 ]
> Stopped at      copyin_nosmap_erms+0xdd:        movl    (%rsi),%edx
> db>
>
> --
> Peter
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It's a known fault in the oss implementation midi parsing code. The easiest
route is to use something else to parse midi for the time being.

OSS was ported over and many outstanding bugs are still laying around.

Best,
Owen