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

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.

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 ... }

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 >> > > > >> > >>