[Crash-utility] Re: [PATCH v4 07/16] Stop stack unwinding at non-kernel address

On Thu, Jul 25, 2024 at 7:59 AM Tao Liu <ltao(a)redhat.com&gt; wrote: > > Hi Lijiang, > > On Wed, Jul 24, 2024 at 6:37 PM lijiang <lijiang(a)redhat.com&gt; wrote: > > > > Hi, Tao > > > > On Tue, Jul 23, 2024 at 2:24 PM lijiang <lijiang(a)redhat.com&gt; wrote: > >> > >> On Tue, Jul 23, 2024 at 1:55 PM Tao Liu <ltao(a)redhat.com&gt; wrote: > >>> > >>> Hi Aditya & Lianbo, > >>> > >>> On Mon, Jun 24, 2024 at 11:46 PM Aditya Gupta <adityag(a)linux.ibm.com&gt; wrote: > >>> > > >>> > Hello Lianbo, > >>> > > >>> > On 24/06/24 05:32PM, lijiang wrote: > >>> > > > <...snip...> > >>> > > > > >>> > > > Before: > >>> > > > crash> gdb bt > >>> > > > #0 0xffffffff816a8f65 in context_switch ... > >>> > > > #1 __schedule () ... > >>> > > > #2 0xffffffff816a94e9 in schedule ... > >>> > > > #3 0xffffffff816a86fd in schedule_hrtimeout_range_clock ... > >>> > > > #4 0xffffffff816a8733 in schedule_hrtimeout_range ... > >>> > > > #5 0xffffffff8124bb7e in ep_poll ... > >>> > > > #6 0xffffffff8124d00d in SYSC_epoll_wait ... > >>> > > > #7 SyS_epoll_wait ... > >>> > > > #8 <signal handler called> > >>> > > > #9 0x00007f0449407923 in ?? () > >>> > > > #10 0xffff880100000001 in ?? () > >>> > > > #11 0xffff880169b3c010 in ?? () > >>> > > > #12 0x0000000000000040 in irq_stack_union () > >>> > > > #13 0xffff880169b3c058 in ?? () > >>> > > > #14 0xffff880169b3c048 in ?? () > >>> > > > #15 0xffff880169b3c050 in ?? () > >>> > > > #16 0x0000000000000000 in ?? () > >>> > > > > >>> > > > After: > >>> > > > crash> gdb bt > >>> > > > #0 0xffffffff816a8f65 in context_switch ... > >>> > > > #1 __schedule () ... > >>> > > > #2 0xffffffff816a94e9 in schedule () ... > >>> > > > #3 0xffffffff816a86fd in schedule_hrtimeout_range_clock ... > >>> > > > #4 0xffffffff816a8733 in schedule_hrtimeout_range ... > >>> > > > #5 0xffffffff8124bb7e in ep_poll ... > >>> > > > #6 0xffffffff8124d00d in SYSC_epoll_wait ... > >>> > > > #7 SyS_epoll_wait ... > >>> > > > #8 <signal handler called> > >>> > > > #9 0x00007f0449407923 in ?? () > >>> > > > > >>> > > > > >>> > > It seems that there are still some non-kernel addresses that do not get > >>> > > filtered. Can you help double check? > >>> > >>> Yes, it is a non-kernel address which does not get filtered. > >>> > >>> > > > >>> > > > >>> > > For example: > >>> > > > >>> > > crash> gdb bt > >>> > > #0 crash_setup_regs (newregs=0xffffb5bb4f197938, oldregs=0x0) at > >>> > > ./arch/x86/include/asm/kexec.h:114 > >>> > > #1 0xffffffff8e61e32e in __crash_kexec (regs=regs@entry=0x0) at > >>> > > kernel/crash_core.c:122 > >>> > > #2 0xffffffff8e51a64d in panic (fmt=fmt@entry=0xffffffff8fa51609 "sysrq > >>> > > triggered crash\n") at kernel/panic.c:366 > >>> > > #3 0xffffffff8ec21f86 in sysrq_handle_crash (key=<optimized out>) at > >>> > > drivers/tty/sysrq.c:154 > >>> > > #4 0xffffffff8ec22550 in __handle_sysrq (key=<optimized out>, > >>> > > check_mask=check_mask@entry=false) at drivers/tty/sysrq.c:612 > >>> > > #5 0xffffffff8ec22bf5 in write_sysrq_trigger (file=<optimized out>, > >>> > > buf=<optimized out>, count=2, ppos=<optimized out>) at > >>> > > drivers/tty/sysrq.c:1183 > >>> > > #6 0xffffffff8e935ae5 in pde_write (ppos=<optimized out>, count=<optimized > >>> > > out>, buf=<optimized out>, file=0xffffb5bb4f197938, pde=0xffff98338b78e0c0) > >>> > > at fs/proc/inode.c:334 > >>> > > #7 proc_reg_write (file=0xffffb5bb4f197938, buf=0x0, count=1, ppos=0x0) at > >>> > > fs/proc/inode.c:346 > >>> > > #8 0xffffffff8e88d382 in vfs_write (file=file@entry=0xffff98338b789200, > >>> > > buf=buf@entry=0x5614d58a22c0 <error: Cannot access memory at address > >>> > > 0x5614d58a22c0>, count=count@entry=2, pos=pos@entry=0xffffb5bb4f197b78) at > >>> > > fs/read_write.c:588 > >>> > > #9 0xffffffff8e88d9ff in ksys_write (fd=<optimized out>, > >>> > > buf=0x5614d58a22c0 <error: Cannot access memory at address 0x5614d58a22c0>, > >>> > > count=2) at fs/read_write.c:643 > >>> > > #10 0xffffffff8f124429 in do_syscall_x64 (nr=1, regs=0xffffb5bb4f197f58) at > >>> > > arch/x86/entry/common.c:52 > >>> > > #11 do_syscall_64 (regs=0xffffb5bb4f197f58, nr=1) at > >>> > > arch/x86/entry/common.c:83 > >>> > > #12 0xffffffff8f20012b in entry_SYSCALL_64 () at > >>> > > arch/x86/entry/entry_64.S:121 > >>> > > #13 0x00007f9a147f69e0 in ?? () > >>> > > > >>> > > The frame #13 looks like a non-kernel address. > >>> > >>> The address usually to be the user space address before entering > >>> kernel, you can see it by: > >>> > >>> crash> gdb bt > >>> ...snip... > >>> #7 SyS_epoll_wait ... > >>> #8 <signal handler called> > >>> #9 0x00007f0449407923 in ?? () > >>> > >>> crash> bt > >>> ...snip... > >>> #6 [ffff880169b3bf80] system_call_fastpath at ffffffff816b5009 > >>> RIP: 00007f0449407923 ... > >>> > >>> So I think leaving the last frame here is useful and shouldn't be > >>> filtered. Though it looks like some garbage data, it can help for some > >>> experienced users... > >> > >> > >> > >> Hmm, normally it should be filtered, otherwise this looks weird. > >> > >> Let me dig into the details and see if that can be filtered out. > > > > > Thanks for your patch! > > > Can you help try this? I saw the non-kernel addresses are filtered out. > > > > + #ifdef CRASH_MERGE > > + extern "C" int is_kvaddr(ulong); > > + #endif > > > > static void > > print_frame (const frame_print_options &fp_opts, > > frame_info *frame, int print_level, > > enum print_what print_what, int print_args, > > struct symtab_and_line sal) > > { > > struct gdbarch *gdbarch = get_frame_arch (frame); > > struct ui_out *uiout = current_uiout; > > enum language funlang = language_unknown; > > struct value_print_options opts; > > struct symbol *func; > > CORE_ADDR pc = 0; > > int pc_p; > > > > pc_p = get_frame_pc_if_available (frame, &pc); > > + #ifdef CRASH_MERGE > > + if (!is_kvaddr(pc)) > > + return; > > + #endif > > ... > > } > > Your code change is "stop printing for non-kernel address", however I > would prefer to "stop stack unwinding for non-kernel address", so I Yes, they are different. If "stop stack unwinding for non-kernel address" won't truncate the backtrace, I would also prefer it. Otherwise I would prefer another one.

> > think it is better to modify it within the for loop, this is where > stack unwinding happens. > > for (fi = trailing; fi && count--; fi = get_prev_frame (fi)) > ... > print_frame_info (fp_opts, fi, 1, LOCATION, 1, 0); > > I made the following code change: > > for (fi = trailing; fi && count--; fi = get_prev_frame (fi)) > { > QUIT; > ... > + CORE_ADDR pc = 0; > + get_frame_pc_if_available (fi, &pc); > + if (!is_kvaddr(pc)) { > + fi = NULL; > + break; > + } > print_frame_info (fp_opts, fi, 1, LOCATION, 1, 0); > > With the change: > > crash> gdb bt > #0 blk_mq_rq_timed_out (req=0xffff880fdb246000, > reserved=reserved@entry=false) at block/blk-mq.c:640 > #1 0xffffffff8130504c in blk_mq_check_expired > (hctx=hctx@entry=0xffff880fda56bc00, rq=<optimized out>, > priv=priv@entry=0xffff880fcf68fde8, reserved=reserved@entry=false) at > block/blk-mq.c:697 > #2 0xffffffff81305eb4 in bt_for_each > (hctx=hctx@entry=0xffff880fda56bc00, bt=bt@entry=0xffff88014c14c310, > off=32, fn=fn@entry=0xffffffff81304ff0 <blk_mq_check_expired>, > data=data@entry=0xffff880fcf68fde8, reserved=reserved@entry=false) at > block/blk-mq-tag.c:431 > #3 0xffffffff8130686e in blk_mq_queue_tag_busy_iter > (q=q@entry=0xffff88004912a340, fn=fn@entry=0xffffffff81304ff0 > <blk_mq_check_expired>, priv=priv@entry=0xffff880fcf68fde8) at > block/blk-mq-tag.c:530 > #4 0xffffffff81301d2b in blk_mq_timeout_work > (work=0xffff88004912ab68) at block/blk-mq.c:730 > #5 0xffffffff810a881a in process_one_work > (worker=worker@entry=0xffff880fd86efa00, work=0xffff88004912ab68) at > kernel/workqueue.c:2252 > #6 0xffffffff810a94e6 in worker_thread (__worker=0xffff880fd86efa00) > at kernel/workqueue.c:2380 > #7 0xffffffff810b098f in kthread (_create=0xffff8801695f7d38) at > kernel/kthread.c:202 > #8 <signal handler called>

^^^^^^^^^^^^^^^^^^^^^^^^ What's this for? Thanks Lianbo > > crash> > > What do you think? > > Thanks, > Tao Liu > > > > > Thanks > > Lianbo > > > >> > >> Thanks > >> Lianbo > >> > >>> > >>> > > >>> > True. Though it seems to be okay for it to print the last frame with a > >>> > non-kernel address, as in this snippet from gdb: > >>> > > >>> > for (fi = trailing; fi && count--; fi = get_prev_frame (fi)) > >>> > ... > >>> > print_frame_info (fp_opts, fi, 1, LOCATION, 1, 0); > >>> > > >>> > Seems that frame #13, fi was not NULL. > >>> > > >>> > Seeing Tao's change, it compares the current frame's NIP/PC to see if > >>> > it should return NULL (which I think is nice and works). Here the > >>> > 'this_frame' would have been frame 12, (which would have called > >>> > `'get_prev_frame' to get the frame 13) > >>> > > >>> > ``` > >>> > frame_pc_p = get_frame_pc_if_available (this_frame, &frame_pc); > >>> > #ifdef CRASH_MERGE > >>> > if (!is_kvaddr(frame_pc)) { > >>> > return NULL; > >>> > } > >>> > #endif > >>> > ``` > >>> > > >>> > Tao's condition will hit when 'get_prev_frame(this_frame=frame#13)' will > >>> > be called to get the frame #14, which will return NULL and hence break > >>> > out of the loop. > >>> > > >>> > This is based on what I recall and a quick look at the implementation, > >>> > please feel free to correct Lianbo/Tao. > >>> > >>> Thanks Aditya for the detailed inspection, which I didn't dive into. > >>> When I notice the last frame to be the userspace address, I just keep > >>> it as it is. > >>> > >>> Thanks, > >>> Tao Liu > >>> > >>> > >>> > > >>> > Thanks, > >>> > Aditya Gupta > >>> > > >>> > > >>> > > > >>> > > > >>> > > Thanks > >>> > > Lianbo > >>> > > > >>> > > > >>> > > > Cc: Sourabh Jain <sourabhjain(a)linux.ibm.com&gt; > >>> > > > Cc: Hari Bathini <hbathini(a)linux.ibm.com&gt; > >>> > > > Cc: Mahesh J Salgaonkar <mahesh(a)linux.ibm.com&gt; > >>> > > > Cc: Naveen N. Rao <naveen.n.rao(a)linux.vnet.ibm.com&gt; > >>> > > > Cc: Lianbo Jiang <lijiang(a)redhat.com&gt; > >>> > > > Cc: HAGIO KAZUHITO(萩尾 一仁) <k-hagio-ab(a)nec.com&gt; > >>> > > > Cc: Tao Liu <ltao(a)redhat.com&gt; > >>> > > > Cc: Alexey Makhalov <alexey.makhalov(a)broadcom.com&gt; > >>> > > > Signed-off-by: Tao Liu <ltao(a)redhat.com&gt; > >>> > > > --- > >>> > > > defs.h | 1 + > >>> > > > gdb-10.2.patch | 26 ++++++++++++++++++++++++++ > >>> > > > gdb_interface.c | 6 ++++++ > >>> > > > 3 files changed, 33 insertions(+) > >>> > > > > >>> > > > diff --git a/defs.h b/defs.h > >>> > > > index 012ffdc..c0e6a29 100644 > >>> > > > --- a/defs.h > >>> > > > +++ b/defs.h > >>> > > > @@ -7902,6 +7902,7 @@ extern unsigned char *gdb_prettyprint_arrays; > >>> > > > extern unsigned int *gdb_repeat_count_threshold; > >>> > > > extern unsigned char *gdb_stop_print_at_null; > >>> > > > extern unsigned int *gdb_output_radix; > >>> > > > +int is_kvaddr(ulong); > >>> > > > > >>> > > > /* > >>> > > > * gdb/top.c > >>> > > > diff --git a/gdb-10.2.patch b/gdb-10.2.patch > >>> > > > index 0bed96a..3ed40c0 100644 > >>> > > > --- a/gdb-10.2.patch > >>> > > > +++ b/gdb-10.2.patch > >>> > > > @@ -16171,3 +16171,29 @@ exit 0 > >>> > > > } > >>> > > > > >>> > > > /* > >>> > > > +--- gdb-10.2/gdb/frame.c.orig > >>> > > > ++++ gdb-10.2/gdb/frame.c > >>> > > > +@@ -2331,6 +2331,10 @@ inside_entry_func (frame_info *this_frame) > >>> > > > + This function should not contain target-dependent tests, such as > >>> > > > + checking whether the program-counter is zero. */ > >>> > > > + > >>> > > > ++#ifdef CRASH_MERGE > >>> > > > ++extern "C" int is_kvaddr(ulong); > >>> > > > ++#endif > >>> > > > ++ > >>> > > > + struct frame_info * > >>> > > > + get_prev_frame (struct frame_info *this_frame) > >>> > > > + { > >>> > > > +@@ -2353,7 +2357,11 @@ get_prev_frame (struct frame_info *this_frame) > >>> > > > + get_frame_id (this_frame); > >>> > > > + > >>> > > > + frame_pc_p = get_frame_pc_if_available (this_frame, &frame_pc); > >>> > > > +- > >>> > > > ++#ifdef CRASH_MERGE > >>> > > > ++ if (!is_kvaddr(frame_pc)) { > >>> > > > ++ return NULL; > >>> > > > ++ } > >>> > > > ++#endif > >>> > > > + /* tausq/2004-12-07: Dummy frames are skipped because it doesn't make > >>> > > > much > >>> > > > + sense to stop unwinding at a dummy frame. One place where a dummy > >>> > > > + frame may have an address "inside_main_func" is on HPUX. On HPUX, > >>> > > > the > >>> > > > diff --git a/gdb_interface.c b/gdb_interface.c > >>> > > > index b13d5fd..e76ecc6 100644 > >>> > > > --- a/gdb_interface.c > >>> > > > +++ b/gdb_interface.c > >>> > > > @@ -947,6 +947,12 @@ gdb_lookup_module_symbol(ulong addr, ulong *offset) > >>> > > > } > >>> > > > } > >>> > > > > >>> > > > +int > >>> > > > +is_kvaddr(ulong addr) > >>> > > > +{ > >>> > > > + return IS_KVADDR(addr); > >>> > > > +} > >>> > > > + > >>> > > > /* > >>> > > > * Used by gdb_interface() to catch gdb-related errors, if desired. > >>> > > > */ > >>> > > > -- > >>> > > > 2.40.1 > >>> > > > > >>> > > >>> >