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MINOR: threads: export the POSIX thread ID in panic dumps 

It is very difficult to map a panic dump against a gdb thread dump
because the thread numbers do not match. However gdb provides the
pthread ID but this one is supposed to be opaque and not to be cast
to a scalar.

This patch provides a fnuction, ha_get_pthread_id() which retrieves
the pthread ID of the indicated thread and casts it to an unsigned
long long so as to lose the least possible amount of information from
it. This is done cleanly using a union to maintain alignment so as
long as these IDs are stored on 1..8 bytes they will be properly
reported. This ID is now presented in the panic dumps so it now
becomes possible to map these threads. When threads are disabled,
zero is returned. For example, this is a panic dump:

  Thread 1 is about to kill the process.
  *>Thread 1 : id=0x7fe92b825180 act=0 glob=0 wq=1 rq=0 tl=0 tlsz=0 rqsz=0
               stuck=1 prof=0 harmless=0 wantrdv=0
               cpu_ns: poll=5119122 now=2009446995 diff=2004327873
               curr_task=0xc99bf0 (task) calls=4 last=0
                 fct=0x592440(task_run_applet) ctx=0xca9c50(<CLI>)
               strm=0xc996a0 src=unix fe=GLOBAL be=GLOBAL dst=<CLI>
               rqf=848202 rqa=0 rpf=80048202 rpa=0 sif=EST,200008 sib=EST,204018
               af=(nil),0 csf=0xc9ba40,8200
               ab=0xca9c50,4 csb=(nil),0
               cof=0xbf0e50,1300:PASS(0xc9cee0)/RAW((nil))/unix_stream(20)
               cob=(nil),0:NONE((nil))/NONE((nil))/NONE(0)
               call trace(20):
               |       0x59e4cf [48 83 c4 10 5b 5d 41 5c]: wdt_handler+0xff/0x10c
               | 0x7fe92c170690 [48 c7 c0 0f 00 00 00 0f]: libpthread:+0x13690
               | 0x7ffce29519d9 [48 c1 e2 20 48 09 d0 48]: linux-vdso:+0x9d9
               | 0x7ffce2951d54 [eb d9 f3 90 e9 1c ff ff]: linux-vdso:__vdso_gettimeofday+0x104/0x133
               |       0x57b484 [48 89 e6 48 8d 7c 24 10]: main+0x157114
               |       0x50ee6a [85 c0 75 76 48 8b 55 38]: main+0xeaafa
               |       0x50f69c [48 63 54 24 20 85 c0 0f]: main+0xeb32c
               |       0x59252c [48 c7 c6 d8 ff ff ff 44]: task_run_applet+0xec/0x88c
    Thread 2 : id=0x7fe92b6e6700 act=0 glob=0 wq=0 rq=0 tl=0 tlsz=0 rqsz=0
               stuck=0 prof=0 harmless=1 wantrdv=0
               cpu_ns: poll=786738 now=1086955 diff=300217
               curr_task=0
    Thread 3 : id=0x7fe92aee5700 act=0 glob=0 wq=0 rq=0 tl=0 tlsz=0 rqsz=0
               stuck=0 prof=0 harmless=1 wantrdv=0
               cpu_ns: poll=828056 now=1129738 diff=301682
               curr_task=0
    Thread 4 : id=0x7fe92a6e4700 act=0 glob=0 wq=0 rq=0 tl=0 tlsz=0 rqsz=0
               stuck=0 prof=0 harmless=1 wantrdv=0
               cpu_ns: poll=818900 now=1153551 diff=334651
               curr_task=0

And this is the gdb output:

  (gdb) info thr
    Id   Target Id                         Frame
  * 1    Thread 0x7fe92b825180 (LWP 15234) 0x00007fe92ba81d6b in raise () from /lib64/libc.so.6
    2    Thread 0x7fe92b6e6700 (LWP 15235) 0x00007fe92bb56a56 in epoll_wait () from /lib64/libc.so.6
    3    Thread 0x7fe92a6e4700 (LWP 15237) 0x00007fe92bb56a56 in epoll_wait () from /lib64/libc.so.6
    4    Thread 0x7fe92aee5700 (LWP 15236) 0x00007fe92bb56a56 in epoll_wait () from /lib64/libc.so.6

We can clearly see that while threads 1 and 2 are the same, gdb's
threads 3 and 4 respectively are haproxy's threads 4 and 3.

This may be backported to 2.0 as it removes some confusion in github issues.
This commit is contained in:
Willy Tarreau 2020-05-01 11:28:49 +02:00
parent 8d2c98b76c
commit ff64d3b027
2 changed files with 38 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

36
include/common/hathreads.h
View File

@ -170,6 +170,11 @@ static inline void ha_set_tid(unsigned int tid)
ti = &ha_thread_info[tid];
}
static inline unsigned long ha_get_pthread_id(unsigned int thr)
{
return 0;
}
static inline void ha_thread_relax(void)
{
#if _POSIX_PRIORITY_SCHEDULING
@ -483,6 +488,37 @@ static inline void ha_set_tid(unsigned int data)
ti = &ha_thread_info[tid];
}
/* Retrieves the opaque pthread_t of thread <thr> cast to an unsigned long long
* since POSIX took great care of not specifying its representation, making it
* hard to export for post-mortem analysis. For this reason we copy it into a
* union and will use the smallest scalar type at least as large as its size,
* which will keep endianness and alignment for all regular sizes. As a last
* resort we end up with a long long ligned to the first bytes in memory, which
* will be endian-dependent if pthread_t is larger than a long long (not seen
* yet).
*/
static inline unsigned long long ha_get_pthread_id(unsigned int thr)
{
union {
pthread_t t;
unsigned long long ll;
unsigned int i;
unsigned short s;
unsigned char c;
} u;
memset(&u, 0, sizeof(u));
u.t = ha_thread_info[thr].pthread;
if (sizeof(u.t) <= sizeof(u.c))
return u.c;
else if (sizeof(u.t) <= sizeof(u.s))
return u.s;
else if (sizeof(u.t) <= sizeof(u.i))
return u.i;
return u.ll;
}
static inline void ha_thread_relax(void)
{
#if _POSIX_PRIORITY_SCHEDULING

3
src/debug.c
View File

@ -58,9 +58,10 @@ void ha_thread_dump(struct buffer *buf, int thr, int calling_tid)
int stuck = !!(ha_thread_info[thr].flags & TI_FL_STUCK);
chunk_appendf(buf,
"%c%cThread %-2u: act=%d glob=%d wq=%d rq=%d tl=%d tlsz=%d rqsz=%d\n"
"%c%cThread %-2u: id=0x%lx act=%d glob=%d wq=%d rq=%d tl=%d tlsz=%d rqsz=%d\n"
" stuck=%d prof=%d",
(thr == calling_tid) ? '*' : ' ', stuck ? '>' : ' ', thr + 1,
ha_get_pthread_id(thr),
thread_has_tasks(),
!!(global_tasks_mask & thr_bit),
!eb_is_empty(&task_per_thread[thr].timers),