Re: [BUG] I found a bug when try to enable record_ftrace

Joel Fernandes
2021-06-08T19:34:14Z

On Wed, Jun 02, 2021 at 10:43:29AM -0700, Kees Cook wrote:
>
> On Wed, Jun 02, 2021 at 03:42:23PM +0800, Zhengyejian (Zetta) wrote:
> > Hello,
> >
> > There may be a deadlock caused by ftrace recursion when try to enable
> > record_ftrace.
>
> Hi,
>
> Thanks for the report. Joel, is this something you can take a look at?

Kees,

Sorry for late reply. Right now I am dealing with a production-stop bug and
would not likely get time. Plus I feel a bit less motivated, because the
ftrace in pstore the way it stands now is unusable due to perf issues anyway
(I wonder if anyone uses it at all now). I would rather someone who has time
to work on this try to revive: https://lkml.org/lkml/2020/9/2/1075 . Should
we just delete pstore function tracing till then?

-Joel

> -Kees
>
> > I'd like to known if the patchset
> > (https://lore.kernel.org/lkml/20201106023235.367190737@goodmis.org/) is
> > trying to fix it.
> >
> > Procedure for reproducing the problem is:
> > 1) this problem appears both in 5.13-rc4 and 5.10;
> >
> > 2) my work environment is:
> > qemu-arm version 4.0.0
> > arm-linux-gnueabi-gcc (Ubuntu/Linaro 7.5.0-3ubuntu1~18.04) 7.5.0
> >
> > 3) then try to enable record_ftrace:
> > / # mount -t pstore pstore /sys/fs/pstore
> > / # echo 1 > /sys/kernel/debug/pstore/record_ftrace
> >
> > 4) then system appears to be stuck, and use arm-linux-gnueabi-gdb dump the
> > following call stack:
> > #0 arch_spin_lock (lock=0x811a0f98) at
> > /home/zyj/Linux/linux-master/arch/arm/include/asm/spinlock.h:74
> > #1 do_raw_spin_lock_flags (flags=<synthetic pointer>, lock=0x811a0f98)
> > at /home/zyj/Linux/linux-master/include/linux/spinlock.h:195
> > #2 __raw_spin_lock_irqsave (lock=0x811a0f98) at
> > /home/zyj/Linux/linux-master/include/linux/spinlock_api_smp.h:119
> > #3 _raw_spin_lock_irqsave (lock=lock@entry=0x811a0f98) at
> > /home/zyj/Linux/linux-master/kernel/locking/spinlock.c:159
> > #4 0x8046c6e0 in buffer_size_add (prz=prz@entry=0x811a0f80,
> > a=a@entry=16) at /home/zyj/Linux/linux-master/fs/pstore/ram_core.c:82
> > #5 0x8046cc20 in persistent_ram_write (prz=0x811a0f80, s=0x81137b80,
> > count=16) at /home/zyj/Linux/linux-master/fs/pstore/ram_core.c:327
> > #6 0x8046b438 in ramoops_pstore_write (record=0x81137b90) at
> > /home/zyj/Linux/linux-master/fs/pstore/ram.c:331
> > #7 0x8046add8 in pstore_ftrace_call (ip=2156609456,
> > parent_ip=2152122068, op=<optimized out>, fregs=<optimized out>)
> > at /home/zyj/Linux/linux-master/fs/pstore/ftrace.c:54
> > #8 0x801dd580 in __ftrace_ops_list_func (ignored=0x0, fregs=0x0,
> > parent_ip=2152122068, ip=2156609456) at
> > /home/zyj/Linux/linux-master/kernel/trace/ftrace.c:7003
> > #9 ftrace_ops_list_func (ip=2156609456, parent_ip=2152122068,
> > op=<optimized out>, fregs=0x0) at
> > /home/zyj/Linux/linux-master/kernel/trace/ftrace.c:7028
> > #10 0x801109f8 in ftrace_caller () at
> > /home/zyj/Linux/linux-master/arch/arm/kernel/entry-ftrace.S:224
> > #11 0x808b3fb4 in _raw_spin_unlock_irqrestore
> > (lock=lock@entry=0x811a0f98, flags=1610612883) at
> > /home/zyj/Linux/linux-master/kernel/locking/spinlock.c:190
> > #12 0x8046c6d4 in buffer_size_add (prz=prz@entry=0x811a0f80,
> > a=a@entry=16) at /home/zyj/Linux/linux-master/fs/pstore/ram_core.c:95
> > #13 0x8046cc20 in persistent_ram_write (prz=0x811a0f80, s=0x81137cf8,
> > count=16) at /home/zyj/Linux/linux-master/fs/pstore/ram_core.c:327
> > #14 0x8046b438 in ramoops_pstore_write (record=0x81137d08) at
> > /home/zyj/Linux/linux-master/fs/pstore/ram.c:331
> > #15 0x8046add8 in pstore_ftrace_call (ip=2148632188,
> > parent_ip=2148601660, op=<optimized out>, fregs=<optimized out>)
> > at /home/zyj/Linux/linux-master/fs/pstore/ftrace.c:54
> > #16 0x801dd580 in __ftrace_ops_list_func (ignored=0x0, fregs=0x0,
> > parent_ip=2148601660, ip=2148632188) at
> > /home/zyj/Linux/linux-master/kernel/trace/ftrace.c:7003
> > #17 ftrace_ops_list_func (ip=2148632188, parent_ip=2148601660,
> > op=<optimized out>, fregs=0x0) at
> > /home/zyj/Linux/linux-master/kernel/trace/ftrace.c:7028
> > #18 0x801109f8 in ftrace_caller () at
> > /home/zyj/Linux/linux-master/arch/arm/kernel/entry-ftrace.S:224
> > #19 0x80118680 in __set_fixmap (idx=idx@entry=FIX_TEXT_POKE0,
> > phys=phys@entry=0, prot=prot@entry=0) at
> > /home/zyj/Linux/linux-master/arch/arm/mm/mmu.c:385
> > #20 0x80110f3c in patch_unmap (flags=<synthetic pointer>, fixmap=129) at
> > /home/zyj/Linux/linux-master/arch/arm/kernel/patch.c:45
> > #21 __patch_text_real (addr=addr@entry=0x808b3fb0
> > <_raw_spin_unlock_irqrestore+16>, insn=insn@entry=3957420680,
> > remap=remap@entry=true)
> > at /home/zyj/Linux/linux-master/arch/arm/kernel/patch.c:104
> > #22 0x80110b40 in __patch_text (insn=3957420680, addr=0x808b3fb0
> > <_raw_spin_unlock_irqrestore+16>) at
> > /home/zyj/Linux/linux-master/arch/arm/include/asm/patch.h:10
> > #23 ftrace_modify_code (pc=2156609456, old=3904716800, new=3957420680,
> > validate=true) at /home/zyj/Linux/linux-master/arch/arm/kernel/ftrace.c:95
> > #24 0x80110cf4 in ftrace_make_call (rec=rec@entry=0x81007ce0,
> > addr=addr@entry=2148600280) at
> > /home/zyj/Linux/linux-master/arch/arm/kernel/ftrace.c:132
> > #25 0x801dda40 in __ftrace_replace_code (rec=rec@entry=0x81007ce0,
> > enable=enable@entry=true) at
> > /home/zyj/Linux/linux-master/kernel/trace/ftrace.c:2524
> > #26 0x801de17c in ftrace_replace_code (mod_flags=mod_flags@entry=1) at
> > /home/zyj/Linux/linux-master/kernel/trace/ftrace.c:2554
> > #27 0x801de39c in ftrace_modify_all_code (command=5) at
> > /home/zyj/Linux/linux-master/kernel/trace/ftrace.c:2698
> > #28 0x80110ad8 in __ftrace_modify_code (data=<optimized out>) at
> > /home/zyj/Linux/linux-master/arch/arm/kernel/ftrace.c:39
> > #29 0x801d4da4 in multi_cpu_stop (data=data@entry=0x81c69d84) at
> > /home/zyj/Linux/linux-master/kernel/stop_machine.c:240
> > #30 0x801d4a14 in cpu_stopper_thread (cpu=<optimized out>) at
> > /home/zyj/Linux/linux-master/kernel/stop_machine.c:511
> > #31 0x8014de3c in smpboot_thread_fn (data=0x810c1c80) at
> > /home/zyj/Linux/linux-master/kernel/smpboot.c:165
> > #32 0x8014a0dc in kthread (_create=0x810c1d40) at
> > /home/zyj/Linux/linux-master/kernel/kthread.c:313
> > #33 0x80100150 in ret_from_fork () at
> > /home/zyj/Linux/linux-master/arch/arm/kernel/entry-common.S:158
> > Backtrace stopped: previous frame identical to this frame (corrupt
> > stack?)
> >
> > See above #7~#15, there is a recursion in function pstore_ftrace_call(), and
> > a spin_lock(lock=0x811a0f98) is hold since unlock operation in above #11 not
> > finished. Then in above #0, trying to acquire same lock cause a deadlock.
> >
> > Enabling 'record_ftrace' seems a basic operation of pstore/ftrace, Does it
> > mean this feature is not available for a while?
> >
> > Best Regards,
> > Zheng
>
> --
> Kees Cook