On Wed, Dec 6, 2017 at 11:13 AM, Olivier <[email protected]> wrote: > > > 2017-12-06 15:52 GMT+01:00 George Joseph <[email protected]>: > >> >> >> On Tue, Dec 5, 2017 at 9:20 AM, Olivier <[email protected]> wrote: >> >>> Hello, >>> >>> I carefully read [1] which details how backtrace files can be produced. >>> >>> Maybe this seems natural to some, but how can I go one step futher, and >>> check that produced XXX-thread1.txt, XXX-brief.txt, ... files are OK ? >>> >>> In other words, where can I find an example on how to use one of those >>> files and check by myself, that if a system ever fails, I won't have to >>> wait for another failure to provide required data to support teams ? >>> >> >> It's a great question but I could spend a week answering it and not >> scratch the surface. :) >> > > Thanks very much for trying, anyway ;-) > > >> It's not a straightforward thing unless you know the code in question. >> The most common is a segmentation fault (segfault or SEGV). >> > > True ! I experienced segfaults lately and I could not configure the > platform I used then (Debian Jessie) to produce core files in a directory > Asterisk can write into. > Now, with Debian Stretch, I can produce core file at will (with a kill -s > SIGSEGV <processid>). > I checked ast_coredumped worked OK as it produced thread.txt files and so > on. > > Ideally, I would like to go one step further: check now that a future .txt > file would be "workable" (and not "you should have compiled with option XXX > or configured with option YYY) . > > > >> In that case, the thread1.txt file is the place to start. Since most >> of the objects passed around are really pointers to objects, the most >> obvious cause would be a 0x0 for a value. So for instance "chan=0x0". >> That would be a pointer to a channel object that was not set when it >> probably should have been. Unfortunately, it's not only 0x0 that could >> cause a segv. Anytime a program tries to access memory it doesn't own, >> that signal is raised. So let's say there a 256 byte buffer which the >> process owns. If there's a bug somewhere that causes the program to try >> and access bytes beyond the end of the buffer, you MAY get a segv if that >> process doesn't also own that memory. If this case, the backtrace won't >> show anything obvious because the pointers all look valid. There probably >> would be an index variable (i or ix, etc) that may be set to 257 but you'd >> have to know that the buffer was only 256 bytes to realize that that was >> the issue. >> > > So, with an artificial kill -s SIGSEGV <processid>, does the bellow > output prove I have a workable .txt files (having .txt files that let > people find the root cause of the issue is another story as we probably can > only hope for the best here) ? > > > # head core-brief.txt > !@!@!@! brief.txt !@!@!@! > > > Thread 38 (Thread 0x7f2aa5dd0700 (LWP 992)): > #0 pthread_cond_timedwait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/ > x86_64/pthread_cond_timedwait.S:225 > #1 0x000055cdcb69ae84 in __ast_cond_timedwait (filename=0x55cdcb7d4910 > "threadpool.c", lineno=1131, func=0x55cdcb7d4ea8 <__PRETTY_FUNCTION__.8978> > "worker_idle", cond_name=0x55cdcb7d4b7f "&worker->cond", > mutex_name=0x55cdcb7d4b71 "&worker->lock", cond=0x7f2abc000978, > t=0x7f2abc0009a8, abstime=0x7f2aa5dcfc30) at lock.c:668 > #2 0x000055cdcb75d153 in worker_idle (worker=0x7f2abc000970) at > threadpool.c:1131 > #3 0x000055cdcb75ce61 in worker_start (arg=0x7f2abc000970) at > threadpool.c:1022 > #4 0x000055cdcb769a8c in dummy_start (data=0x7f2abc000a80) at utils.c:1238 > #5 0x00007f2aeddad494 in start_thread (arg=0x7f2aa5dd0700) at > pthread_create.c:333 >
That's it! The key pieces of information are the function names (worker_idle, worker_start, etc.), the filename (threadpool.c, etc) and the line numbers (1131, 1022, etc). > > >> Deadlocks are even harder to troubleshoot. For that, you need to look at >> full.txt to see where the threads are stuck and find the 1 thread that's >> holding the lock that the others are stuck on. >> >> Sorry. I wish I had a better answer because it'd help a lot if folks >> could do more investigation themselves. >> >> >> >> >> >>> >>> >>>
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