Hi Aditya,
On Tue, Mar 12, 2024 at 5:12 PM Aditya Gupta <adityag@xxxxxxxxxxxxx> wrote:
>
> Hi Tao,
>
> On Thu, Mar 07, 2024 at 08:52:40PM +0800, Tao Liu wrote:
> > Previously we can only view the stack unwinding for the tasks which are
> > running on each CPUs. This patch will enable the ability to view
> > arbitrary tasks stack unwinding.
> >
> > After crash get initialized, "info threads" will output like the
> > following:
> >
> > crash> info threads
> > Id Target Id Frame
> > 1 CPU 0 native_safe_halt () at arch/x86/include/asm/irqflags.h:54
> > ...
> > * 8 CPU 7 blk_mq_rq_timed_out (req=0xffff880fdb246000, reserved=reserved@entry=false) at block/blk-mq.c:640
> > ...
> > 13 CPU 12 <unavailable> in ?? ()
> > 14 CPU 13 native_safe_halt () at arch/x86/include/asm/irqflags.h:54
> > ...
> >
> > crash> ps
> > PID PPID CPU TASK ST %MEM VSZ RSS COMM
> > > 0 0 0 ffffffff819f9480 RU 0.0 0 0 [swapper/0]
> > > 0 0 1 ffff880169411fa0 RU 0.0 0 0 [swapper/1]
> > ...
> > 0 0 23 ffff8801694e0000 RU 0.0 0 0 [swapper/23]
> > 1 0 13 ffff880169b30000 IN 0.0 193052 4180 systemd
> >
> > "info threads" show the tasks which are currently running on each CPU. If we'd
> > like to view systemd task's stack unwinding, which is inactive status, we
> > do the following:
> >
> > crash> set 1
> > or
> > crash> set ffff880169b30000
> >
> > Then the register cache of systemd will be swapped into CPU 13:
> >
> > crash> info threads
> > Id Target Id Frame
> > 1 CPU 0 native_safe_halt () at arch/x86/include/asm/irqflags.h:54
> > ...
> > 8 CPU 7 blk_mq_rq_timed_out (req=0xffff880fdb246000, reserved=reserved@entry=false) at block/blk-mq.c:640
> > ...
> > 13 CPU 12 <unavailable> in ?? ()
> > * 14 CPU 13 0xffffffff816a8f65 in context_switch (rq=0x0, next=0x0, prev=0xffff880169b30000) at kernel/sched/core.c:2527
> > ...
> >
> > And we can view the stack unwinding of systemd:
> >
> > crash> bt
> > PID: 1 TASK: ffff880169b30000 CPU: 13 COMMAND: "systemd"
> > #0 [ffff880169b3bd58] __schedule at ffffffff816a8f65
> > #1 [ffff880169b3bdc0] schedule at ffffffff816a94e9
> > #2 [ffff880169b3bdd0] schedule_hrtimeout_range_clock at ffffffff816a86fd
> > #3 [ffff880169b3be68] schedule_hrtimeout_range at ffffffff816a8733
> > #4 [ffff880169b3be78] ep_poll at ffffffff8124bb7e
> > #5 [ffff880169b3bf30] sys_epoll_wait at ffffffff8124d00d
> > #6 [ffff880169b3bf80] system_call_fastpath at ffffffff816b5009
> > RIP: 00007f0449407923 RSP: 00007ffc35a3c378 RFLAGS: 00010246
> > RAX: 00000000000000e8 RBX: ffffffff816b5009 RCX: 0000000000000071
> > RDX: 000000000000001d RSI: 00007ffc35a3d5a0 RDI: 0000000000000004
> > RBP: 00007ffc35a3d810 R8: 0000000000000000 R9: 0000000000000000
> > R10: 00000000ffffffff R11: 0000000000000293 R12: 0000563ca2ebe980
> > R13: 0000000000000003 R14: ffffffffffffffff R15: 0000000000000001
> > ORIG_RAX: 00000000000000e8 CS: 0033 SS: 002b
> > crash> gdb bt
> > #0 0xffffffff816a8f65 in context_switch (rq=0x0, next=0x0, prev=0xffff880169b30000) at kernel/sched/core.c:2527
> > #1 __schedule () at kernel/sched/core.c:3540
> > #2 0xffffffff816a94e9 in schedule () at kernel/sched/core.c:3577
> > #3 0xffffffff816a86fd in schedule_hrtimeout_range_clock (expires=expires@entry=0x0, delta=delta@entry=0, mode=mode@entry=HRTIMER_MODE_ABS, clock=clock@entry=1) at kernel/hrtimer.c:1724
> > #4 0xffffffff816a8733 in schedule_hrtimeout_range (expires=expires@entry=0x0, delta=delta@entry=0, mode=mode@entry=HRTIMER_MODE_ABS) at kernel/hrtimer.c:1778
> > #5 0xffffffff8124bb7e in ep_poll (ep=0xffff880fd861f8c0, events=events@entry=0x7ffc35a3d5a0, maxevents=maxevents@entry=29, timeout=timeout@entry=-1) at fs/eventpoll.c:1669
> > #6 0xffffffff8124d00d in SYSC_epoll_wait (timeout=<optimized out>, maxevents=29, events=<optimized out>, epfd=<optimized out>) at fs/eventpoll.c:2043
> > #7 SyS_epoll_wait (epfd=<optimized out>, events=140721208415648, maxevents=29, timeout=4294967295) at fs/eventpoll.c:2008
> > #8 <signal handler called>
> > #9 0x00007f0449407923 in ?? ()
> >
> > Signed-off-by: Tao Liu <ltao@xxxxxxxxxx>
> > ---
> > crash_target.c | 50 ++++++++++++++++-------------
> > defs.h | 3 +-
> > gdb-10.2.patch | 85 +-------------------------------------------------
> > kernel.c | 22 +++++++++++++
> > task.c | 5 +--
> > 5 files changed, 57 insertions(+), 108 deletions(-)
> >
> > diff --git a/crash_target.c b/crash_target.c
> > index d06383f..8efe2d6 100644
> > --- a/crash_target.c
> > +++ b/crash_target.c
> > @@ -29,10 +29,10 @@ extern "C" int gdb_readmem_callback(unsigned long, void *, int, int);
> > extern "C" int crash_get_nr_cpus(void);
> > extern "C" int crash_get_cpu_reg (int cpu, int regno, const char *regname,
> > int regsize, void *val);
> > -extern "C" int gdb_change_cpu_context (unsigned int cpu);
> > extern "C" void gdb_refresh_regcache(unsigned int cpu);
> > extern "C" int set_cpu(int cpu, int print_context);
> > -
> > +extern "C" int crash_set_thread(ulong);
> > +extern "C" int gdb_change_thread_context (ulong);
> >
> > /* The crash target. */
> >
> > @@ -110,11 +110,13 @@ crash_target::xfer_partial (enum target_object object, const char *annex,
> >
> > #define CRASH_INFERIOR_PID 1
> >
> > +crash_target *target = NULL;
> > +
> > void
> > crash_target_init (void)
> > {
> > int nr_cpus = crash_get_nr_cpus();
> > - crash_target *target = new crash_target ();
> > + target = new crash_target ();
> >
> > /* Own the target until it is successfully pushed. */
> > target_ops_up target_holder (target);
> > @@ -137,29 +139,35 @@ crash_target_init (void)
> > reinit_frame_cache ();
> > }
> >
> > -/*
> > - * Change gdb's thread context to the thread on given CPU
> > - **/
> > extern "C" int
> > -gdb_change_cpu_context(unsigned int cpu)
> > +gdb_change_thread_context (ulong task)
> > {
> > - ptid_t ptid = ptid_t(CRASH_INFERIOR_PID, 0, cpu);
> > - inferior *inf = current_inferior ();
> > - thread_info *tp = find_thread_ptid (inf, ptid);
> > -
> > - if (tp == nullptr)
> > + int tried = 0;
> > + inferior* inf = current_inferior();
> > + int cpu = crash_set_thread(task);
> > + if (cpu < 0)
> > return FALSE;
> >
> > - /* Making sure that crash's context is same */
> > - set_cpu(cpu, FALSE);
> > -
> > - /* Switch to the thread */
> > - switch_to_thread(tp);
> > -
> > - /* Fetch/Refresh thread's registers */
> > - gdb_refresh_regcache(cpu);
> > + ptid_t ptid = ptid_t(CRASH_INFERIOR_PID, 0, cpu);
> >
> > - return TRUE;
> > +retry:
> > + thread_info *tp = find_thread_ptid (inf, ptid);
> > + if (tp == nullptr && !tried) {
> > + thread_info *thread = add_thread_silent(target,
> > + ptid_t(CRASH_INFERIOR_PID, 0, cpu));
>
> A minor comment.
> Is it possible to do it without needing 'target' as global ? I see
> there's 'inf->current_top_target()', but it's return type if target_ops,
> don't know if it can be used.
>
Thanks for your comments, however I guess it is not workable for the
code change. What we want is to add a thread to the target. I found
one function "target.c:new_thread", which can be used as
"new_thread(current_inferior(), ptid_t(CRASH_INFERIOR_PID, 0, cpu));"
to replace the "add_thread_silent()" code, except we need to make
"new_thread" to be non-static.
I prefer to keep the code as current, because I don't see the side
effect of making target as global variable. What do you think?
> > + tried++;
> > + if (thread) {
> > + goto retry;
> > + }
> > + }
> > +
> > + if (tp == nullptr && tried)
> > + return FALSE;
> > +
> > + target_fetch_registers(get_thread_regcache(tp), -1);
> > + switch_to_thread(tp);
> > + reinit_frame_cache ();
> > + return TRUE;
> > }
> >
> > /* Refresh regcache of gdb thread on given CPU
> > diff --git a/defs.h b/defs.h
> > index 06bd27d..1ddfc5e 100644
> > --- a/defs.h
> > +++ b/defs.h
> > @@ -6083,6 +6083,7 @@ void sort_tgid_array(void);
> > int sort_by_tgid(const void *, const void *);
> > int in_irq_ctx(ulonglong, int, ulong);
> > void check_stack_overflow(void);
> > +int gdb_change_thread_context (ulong);
> >
> > /*
> > * extensions.c
> > @@ -6123,6 +6124,7 @@ void dump_kernel_table(int);
> > void dump_bt_info(struct bt_info *, char *where);
> > void dump_log(int);
> > void parse_kernel_version(char *);
> > +int crash_set_thread(ulong);
> >
> > #define LOG_LEVEL(v) ((v) & 0x07)
> > #define SHOW_LOG_LEVEL (0x1)
> > @@ -8191,7 +8193,6 @@ enum ppc64_regnum {
> > };
> >
> > /* crash_target.c */
> > -extern int gdb_change_cpu_context (unsigned int cpu);
> > extern void gdb_refresh_regcache (unsigned int cpu);
> >
> > #endif /* !GDB_COMMON */
> > diff --git a/gdb-10.2.patch b/gdb-10.2.patch
> > index 138413f..3e6677d 100644
> > --- a/gdb-10.2.patch
> > +++ b/gdb-10.2.patch
> > @@ -16058,35 +16058,6 @@ exit 0
> > m10200-dis.c
> > m10200-opc.c
> > m10300-dis.c
> > ---- gdb-10.2/gdb/thread.c.orig
> > -+++ gdb-10.2/gdb/thread.c
> > -@@ -58,6 +58,11 @@ static int highest_thread_num;
> > - /* The current/selected thread. */
> > - static thread_info *current_thread_;
> > -
> > -+#ifdef CRASH_MERGE
> > -+/* Function to set cpu, defined by crash-utility */
> > -+extern "C" void set_cpu (int);
> > -+#endif
> > -+
> > - /* RAII type used to increase / decrease the refcount of each thread
> > - in a given list of threads. */
> > -
> > -@@ -1896,7 +1901,13 @@ thread_command (const char *tidstr, int from_tty)
> > - {
> > - ptid_t previous_ptid = inferior_ptid;
> > -
> > -- thread_select (tidstr, parse_thread_id (tidstr, NULL));
> > -+ struct thread_info* thread_id = parse_thread_id (tidstr, NULL);
> > -+
> > -+#ifdef CRASH_MERGE
> > -+ set_cpu(thread_id->ptid.tid());
> > -+#endif
> > -+
> > -+ thread_select (tidstr, thread_id);
> > -
> > - /* Print if the thread has not changed, otherwise an event will
> > - be sent. */
> > --- gdb-10.2/gdb/ui-file.h.orig
> > +++ gdb-10.2/gdb/ui-file.h
> > @@ -195,6 +195,7 @@ public:
> > @@ -16139,58 +16110,4 @@ exit 0
> > + (dynamic_cast<stdio_file *>gdb_stderr)->set_stream(original_stderr_stream);
> > }
> >
> > - /*
> > ---- gdb-10.2/gdb/thread.c.orig
> > -+++ gdb-10.2/gdb/thread.c
> > -@@ -60,7 +60,7 @@ static thread_info *current_thread_;
> > -
> > - #ifdef CRASH_MERGE
> > - /* Function to set cpu, defined by crash-utility */
> > --extern "C" void set_cpu (int);
> > -+extern "C" void set_cpu(int cpu, int print_context);
> > - #endif
> > -
> > - /* RAII type used to increase / decrease the refcount of each thread
> > -@@ -1098,6 +1098,9 @@ print_thread_info_1 (struct ui_out *uiout, const char *requested_threads,
> > - uiout->table_body ();
> > - }
> > -
> > -+#ifdef CRASH_MERGE
> > -+ int current_cpu = current_thread ? current_thread->ptid.tid() : 0;
> > -+#endif
> > - for (inferior *inf : all_inferiors ())
> > - for (thread_info *tp : inf->threads ())
> > - {
> > -@@ -1113,6 +1116,11 @@ print_thread_info_1 (struct ui_out *uiout, const char *requested_threads,
> > -
> > - ui_out_emit_tuple tuple_emitter (uiout, NULL);
> > -
> > -+ /* Switch to the thread's CPU in crash */
> > -+#ifdef CRASH_MERGE
> > -+ set_cpu(tp->ptid.tid(), FALSE);
> > -+#endif
> > -+
> > - if (!uiout->is_mi_like_p ())
> > - {
> > - if (tp == current_thread)
> > -@@ -1185,6 +1193,11 @@ print_thread_info_1 (struct ui_out *uiout, const char *requested_threads,
> > - /* This end scope restores the current thread and the frame
> > - selected before the "info threads" command, and it finishes the
> > - ui-out list or table. */
> > -+
> > -+#ifdef CRASH_MERGE
> > -+ /* Restore crash's context */
> > -+ set_cpu(current_cpu, FALSE);
> > -+#endif
> > - }
> > -
> > - if (pid == -1 && requested_threads == NULL)
> > -@@ -1904,7 +1917,7 @@ thread_command (const char *tidstr, int from_tty)
> > - struct thread_info* thread_id = parse_thread_id (tidstr, NULL);
> > -
> > - #ifdef CRASH_MERGE
> > -- set_cpu(thread_id->ptid.tid());
> > -+ set_cpu(thread_id->ptid.tid(), FALSE);
> > - #endif
> > -
> > - thread_select (tidstr, thread_id);
> > + /*
> > \ No newline at end of file
> > diff --git a/kernel.c b/kernel.c
> > index c7de73a..49d422b 100644
> > --- a/kernel.c
> > +++ b/kernel.c
> > @@ -6543,6 +6543,28 @@ set_cpu(int cpu, int print_context)
> > show_context(CURRENT_CONTEXT());
> > }
> >
> > +int
> > +crash_set_thread(ulong task)
> > +{
> > + bool found = FALSE;
> > + struct task_context *tc = FIRST_CONTEXT();
> > +
> > + for (int i = 0; i < RUNNING_TASKS(); i++, tc++) {
> > + if (tc->task == task) {
> > + found = TRUE;
> > + break;
> > + }
> > + }
> > +
> > + if (!found)
> > + return -1;
> > +
> > + if (CURRENT_TASK() == tc->task)
> > + return tc->processor;
> > +
> > + set_context(tc->task, NO_PID, TRUE);
> > + return tc->processor;
> > +}
> >
> > /*
> > * Collect the irq_desc[] entry along with its associated handler and
> > diff --git a/task.c b/task.c
> > index a405b05..ef79f53 100644
> > --- a/task.c
> > +++ b/task.c
> > @@ -715,7 +715,8 @@ task_init(void)
> > * crash_target::fetch_registers, so CPU 0's registers are shown as
> > * <unavailable> in gdb mode
> > * */
> > - gdb_refresh_regcache(0);
> > + for (int i = 0; i < get_cpus_online(); i++)
> > + gdb_refresh_regcache(i);
>
> Does x86 require all regcache(s) to be refreshed at init time ?
>
> Till v4 of my ppc series, I also was doing refresh of all CPUs, but it's
> better to do it when required, and there was a review in v4, patch 5
> from Lianbo, quoting it here:
>
> > In addition, I haven't tested how far it takes the time in the
> > multi-core environment, is it possible to implement a smaller
> > granularity refresh operation? For example: When we need switch to
> > another cpu, execute the refresh operation for corresponding regcache.
>
> CPU 0's refresh is required due to gdb having already tried to
> initialised registers before we initialised crash_target
>
> This might add a small noticeable delay on vmcores from big systems.
>
> Adds around 4.6 seconds for a ppc64 vmcore with 64 CPUs, in crash init
> time, while reading it on a fast 48 cpu Power8 system.
> This overhead is less for systems with less CPUs, eg. ~0.43 seconds, on
> a vmcore of 8 CPUs x86_64 system.
Yes, thanks for the testing results. There do have performance
downgrades of refreshing all cpu caches. But this will give correct
results when user type "info threads" after showing "crash>":
With all cpu cache refreshed:
crash> info threads
Id Target Id Frame
1 CPU 0 native_safe_halt () at
arch/x86/include/asm/irqflags.h:54
2 CPU 1 native_safe_halt () at
arch/x86/include/asm/irqflags.h:54
3 CPU 2 <unavailable> in ?? ()
4 CPU 3 <unavailable> in ?? ()
5 CPU 4 native_safe_halt () at
arch/x86/include/asm/irqflags.h:54
6 CPU 5 <unavailable> in ?? ()
7 CPU 6 <unavailable> in ?? ()
* 8 CPU 7 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
9 CPU 8 native_safe_halt () at
arch/x86/include/asm/irqflags.h:54
10 CPU 9 <unavailable> in ?? ()
11 CPU 10 <unavailable> in ?? ()
12 CPU 11 native_safe_halt () at
arch/x86/include/asm/irqflags.h:54
13 CPU 12 <unavailable> in ?? ()
14 CPU 13 native_safe_halt () at
arch/x86/include/asm/irqflags.h:54
15 CPU 14 <unavailable> in ?? ()
16 CPU 15 <unavailable> in ?? ()
17 CPU 16 <unavailable> in ?? ()
18 CPU 17 native_safe_halt () at
arch/x86/include/asm/irqflags.h:54
19 CPU 18 native_safe_halt () at
arch/x86/include/asm/irqflags.h:54
20 CPU 19 <unavailable> in ?? ()
21 CPU 20 <unavailable> in ?? ()
22 CPU 21 <unavailable> in ?? ()
23 CPU 22 native_safe_halt () at
arch/x86/include/asm/irqflags.h:54
24 CPU 23 <unavailable> in ?? ()
crash> q
With only cpu0 refreshed:
crash> info threads
Id Target Id Frame
1 CPU 0 native_safe_halt () at
arch/x86/include/asm/irqflags.h:54
2 CPU 1 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
3 CPU 2 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
4 CPU 3 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
5 CPU 4 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
6 CPU 5 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
7 CPU 6 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
* 8 CPU 7 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
9 CPU 8 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
10 CPU 9 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
11 CPU 10 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
12 CPU 11 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
13 CPU 12 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
14 CPU 13 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
15 CPU 14 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
16 CPU 15 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
17 CPU 16 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
18 CPU 17 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
19 CPU 18 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
20 CPU 19 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
21 CPU 20 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
22 CPU 21 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
23 CPU 22 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
24 CPU 23 blk_mq_rq_timed_out (req=0xffff880fdb246000,
reserved=reserved@entry=false) at block/blk-mq.c:640
As we can see, other cpus[1-6, 8-23] just take the reg cache of
cpu[7], which is incorrect. And if users go further like, "thread 20"
and "gdb bt", it will also give incorrect stack traces.
The cpu cache will only get refreshed once user type "set <pid>", so
the cpu cache will be refreshed by the <pid> task's context.
I doubt a user will understand all the details and constraints, so I'm
afraid the user will be confused by the faulty output. But I also have
no objection if the performance is the priority. Basically it is a
balance of pays and gains. In addition, since cmd "info" and "thread"
is a command provided by gdb, currently I don't know how to hack
those, so cpu cache can be refreshed when "info threads" or "thread
<num>" have been invoked.
Do you have any thoughts?
Thanks,
Tao Liu
>
> Thanks,
> Aditya Gupta
>
> >
> > tt->flags |= TASK_INIT_DONE;
> > }
> > @@ -5315,7 +5316,7 @@ set_context(ulong task, ulong pid, uint update_gdb_thread)
> >
> > /* change the selected thread in gdb, according to current context */
> > if (update_gdb_thread)
> > - return gdb_change_cpu_context(tc->processor);
> > + return gdb_change_thread_context(tc->task);
> > else
> > return TRUE;
> > } else {
> > --
> > 2.40.1
> >
>
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