SIGSEV encountered when creating threads in a loop w/ --gc:arc #13935

zacharycarter · 2020-04-09T17:39:24Z

SIGSEV encountered when creating threads in a loop w/ --gc:arc.

Example

import osproc

var threads: seq[Thread[int]]

proc threadFn(a: int) {.thread.} =
  echo a

let numThreads = countProcessors() - 1

threads.setLen(numThreads)

for i in 0 ..< numThreads:
  createThread(threads[i], threadFn, i)
joinThreads(threads)

Current output

➜  junkers git:(master) ✗ nim c --gc:arc --threads:on --debugger:native -r thread_error.nim
Hint: used config file '/Users/zacharycarter/.choosenim/toolchains/nim-#devel/config/nim.cfg' [Conf]
Hint: system [Processing]
Hint: repr_v2 [Processing]
Hint: widestrs [Processing]
Hint: io [Processing]
Hint: thread_error [Processing]
Hint: osproc [Processing]
Hint: strutils [Processing]
Hint: parseutils [Processing]
Hint: math [Processing]
Hint: bitops [Processing]
Hint: macros [Processing]
Hint: algorithm [Processing]
Hint: unicode [Processing]
Hint: os [Processing]
Hint: pathnorm [Processing]
Hint: osseps [Processing]
Hint: posix [Processing]
Hint: times [Processing]
Hint: options [Processing]
Hint: typetraits [Processing]
Hint: strtabs [Processing]
Hint: hashes [Processing]
Hint: streams [Processing]
Hint: cpuinfo [Processing]
Hint: kqueue [Processing]
CC: stdlib_system.nim
CC: thread_error.nim
Hint:  [Link]
Hint: dsymutil /Users/zacharycarter/dev/junkers/thread_error [Exec]
Hint: 39581 LOC; 0.993 sec; 52.48MiB peakmem; Debug build; proj: /Users/zacharycarter/dev/junkers/thread_error.nim; out: /Users/zacharycarter/dev/junkers/thread_error [SuccessX]
Hint: /Users/zacharycarter/dev/junkers/thread_error  [Exec]
0
3
2
No stack traceback available
SIGSEGV: Illegal storage access. (Attempt to read from nil?)
1
5
No stack traceback available
SIGSEGV: Illegal storage access. (Attempt to read from nil?)
4

Additional Information

https://gist.github.com/zacharycarter/dbee66c50a6c26e7f187512235c4ed1f

➜  junkers git:(master) ✗ nim -v
Nim Compiler Version 1.3.1 [MacOSX: amd64]
Compiled at 2020-04-09
Copyright (c) 2006-2020 by Andreas Rumpf

active boot switches: -d:release

The text was updated successfully, but these errors were encountered:

cooldome · 2020-04-15T14:46:43Z

Hi,
Could you please provide more details like what c/cpp compiler you have used and details OS version. I wan't this one fixed, but I can't replicate it on my PC.
It is likely are a reason for failed tests of #13897, but I can't progress because everything just works for me.

zacharycarter · 2020-04-15T16:29:38Z

@cooldome - sure

I'm using clang / clang++ and OS is macOS Mojave 10.14.6 (18G103)

cooldome · 2020-04-15T19:34:52Z

Hmm, I am using the same and it works for me. Looks like I can't help.

ghost · 2020-04-15T19:37:32Z

@cooldome I can reproduce this behaviour with -d:release (or -d:danger), in debug build it just hangs forever, I'm on Linux amd64 (Bedrock Linux) on latest devel, maybe I can help you debug this?

I compile and run like nim c --threads:on -d:danger --gc:arc -r main.nim.

Seems like it hangs if I compile with --stacktrace:on and if I compile with --stacktrace:off (or with -d:release or -d:danger) it crashes.

ghost · 2020-04-15T19:47:19Z

gdb backtrace after nim c --stacktrace:off --debugger:native --threads:on --gc:arc b.nim

Reading symbols from ./b...
(gdb) run
Starting program: /home/dian/Projects/data/b 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
[New Thread 0x7ffff7be9700 (LWP 14579)]
0
[New Thread 0x7ffff79e8700 (LWP 14580)]
[Thread 0x7ffff7be9700 (LWP 14579) exited]
1
[New Thread 0x7ffff77e7700 (LWP 14581)]

Thread 3 "b" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7ffff79e8700 (LWP 14580)]
0x0000000000401ace in del__Io5JDKCS5u26IEWw0J53hQ (a=a@entry=0x409180 <sharedHeap__R3bhvQCN0d6AYpkvxfT9aGw>, t=t@entry=0x40c228 <sharedHeap__R3bhvQCN0d6AYpkvxfT9aGw+12456>, 
    x=x@entry=140737349857312) at /home/dian/.nim/lib/system/avltree.nim:74
74        if isBottom(t): return
(gdb) bt
#0  0x0000000000401ace in del__Io5JDKCS5u26IEWw0J53hQ (a=a@entry=0x409180 <sharedHeap__R3bhvQCN0d6AYpkvxfT9aGw>, t=t@entry=0x40c228 <sharedHeap__R3bhvQCN0d6AYpkvxfT9aGw+12456>, 
    x=x@entry=140737349857312) at /home/dian/.nim/lib/system/avltree.nim:74
#1  0x0000000000401d58 in rawDealloc__K7uQ6aTKvW6OnOV8EMoNNQ (a=a@entry=0x409180 <sharedHeap__R3bhvQCN0d6AYpkvxfT9aGw>, p=p@entry=0x7ffff7beb038) at /home/dian/.nim/lib/system/alloc.nim:867
#2  0x0000000000401dd5 in dealloc__Jg1OaY9ahkT3MBopLAXRSGw (allocator=allocator@entry=0x409180 <sharedHeap__R3bhvQCN0d6AYpkvxfT9aGw>, p=p@entry=0x7ffff7beb038)
    at /home/dian/.nim/lib/system/alloc.nim:968
#3  0x0000000000401df9 in deallocSharedImpl__lmwgHsdhTsrQaepFju8wew (p=p@entry=0x7ffff7beb038) at /home/dian/.nim/lib/system/alloc.nim:1083
#4  0x0000000000401e10 in deallocShared (p=p@entry=0x7ffff7beb038) at /home/dian/.nim/lib/system/memalloc.nim:295
#5  0x0000000000404b41 in threadProcWrapper__oTnP9cUoE9cVTUL7iHAoIIAA (closure=0x7ffff7bea060) at /home/dian/.nim/lib/system/threads.nim:187
#6  0x00007ffff7e3df27 in start_thread (arg=<optimized out>) at pthread_create.c:479
#7  0x00007ffff7d6ee0f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

ghost · 2020-04-15T19:56:28Z

@cooldome I just checked and I have the same behaviour with your #13897 :

$ bin/nim -v
Nim Compiler Version 1.3.1 [Linux: amd64]
Compiled at 2020-04-15
Copyright (c) 2006-2020 by Andreas Rumpf

git hash: aeaaad38674a7c8302461b208ad8824f7179a3c8
active boot switches: -d:release

$  bin/nim c --stacktrace:off --debugger:native --threads:on --gc:arc b.nim
...

And GDB:

Reading symbols from ./b...
(gdb) run
Starting program: /home/dian/Stuff/nim/b 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
[New Thread 0x7ffff7be9700 (LWP 23636)]
0
[New Thread 0x7ffff79e8700 (LWP 23637)]
[Thread 0x7ffff7be9700 (LWP 23636) exited]
1

Thread 3 "b" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7ffff79e8700 (LWP 23637)]
0x0000000000401ace in del__Io5JDKCS5u26IEWw0J53hQ (a=a@entry=0x409180 <sharedHeap__R3bhvQCN0d6AYpkvxfT9aGw>, 
    t=t@entry=0x40c228 <sharedHeap__R3bhvQCN0d6AYpkvxfT9aGw+12456>, x=x@entry=140737349857312)
    at /home/dian/Stuff/nim/lib/system/avltree.nim:74
74        if isBottom(t): return
(gdb) bt
#0  0x0000000000401ace in del__Io5JDKCS5u26IEWw0J53hQ (a=a@entry=0x409180 <sharedHeap__R3bhvQCN0d6AYpkvxfT9aGw>, 
    t=t@entry=0x40c228 <sharedHeap__R3bhvQCN0d6AYpkvxfT9aGw+12456>, x=x@entry=140737349857312)
    at /home/dian/Stuff/nim/lib/system/avltree.nim:74
#1  0x0000000000401d58 in rawDealloc__K7uQ6aTKvW6OnOV8EMoNNQ (
    a=a@entry=0x409180 <sharedHeap__R3bhvQCN0d6AYpkvxfT9aGw>, p=p@entry=0x7ffff7beb038)
    at /home/dian/Stuff/nim/lib/system/alloc.nim:867
#2  0x0000000000401dd5 in dealloc__Jg1OaY9ahkT3MBopLAXRSGw (
    allocator=allocator@entry=0x409180 <sharedHeap__R3bhvQCN0d6AYpkvxfT9aGw>, p=p@entry=0x7ffff7beb038)
    at /home/dian/Stuff/nim/lib/system/alloc.nim:968
#3  0x0000000000401df9 in deallocSharedImpl__lmwgHsdhTsrQaepFju8wew (p=p@entry=0x7ffff7beb038)
    at /home/dian/Stuff/nim/lib/system/alloc.nim:1083
#4  0x0000000000401e10 in deallocShared (p=p@entry=0x7ffff7beb038)
    at /home/dian/Stuff/nim/lib/system/memalloc.nim:295
#5  0x0000000000404b91 in threadProcWrapper__oTnP9cUoE9cVTUL7iHAoIIAA (closure=0x7ffff7bea060)
    at /home/dian/Stuff/nim/lib/system/threads.nim:187
#6  0x00007ffff7e3df27 in start_thread (arg=<optimized out>) at pthread_create.c:479
#7  0x00007ffff7d6ee0f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

cooldome · 2020-04-15T20:25:15Z

Yes, I can replicate it now. I found that it works if you compile with cpp nim cpp --threads:on -d:danger --gc:arc -r. @Yardanico, @zacharycarter could you please confirm you are getting the same behavior?

I also found it works with old nim 1.1.1 built on 2019-12-09 so it is some kind of regression likely exception handling related.

ghost · 2020-04-15T20:47:54Z

@cooldome weirdly enough I still get SIGSEGV.

I tried using git bisect for the first time and with it found that be795bb (#13280) is the commit that broke this code (the commit before - 84e8477 - works just fine)

ghost · 2020-04-15T21:29:54Z

Also tried running with ./koch temp c -d:useSysAssert --threads:on --gc:arc -r b.nim
(it was broken but I moved rawWrite in system.nim after the import of "system/ansi_c" and commented the only usage of it in seqs_v2 and it worked):

[SYSASSERT] sizeof FreeCell

that sysassert comes from mmdisp.nim line 87:

sysAssert(sizeof(Cell) == sizeof(FreeCell), "sizeof FreeCell")

Cell seems to be of sizeof 8, FreeCell - 16
cc @Araq I guess?

P.S.: It just works (:tm: ) if I comment line 867 in alloc.nim:
del(a, a.root, cast[int](addr(c.data)))
, but that's obviously not correct (although valgrind shows no leaks)

Araq · 2020-04-16T09:13:07Z

@Yardanico that assertion is simply wrong for ARC.

zacharycarter · 2020-04-17T12:18:00Z

@cooldome confirmed that if I compile with nim cpp --threads:on -d:danger --gc:arc -r it works.

zacharycarter · 2020-04-17T15:21:03Z

I believe it was actually this commit / PR which introduced the issue:

c334486
#12977

Note: --gc:arc --exceptions:setjmp works.

ghost · 2020-05-16T11:10:02Z

@Araq it still seems to be broken on devel - hangs without --stackTrace:off and crashed with it

ghost · 2020-05-16T11:16:24Z

Some logs:

2
0
/home/dian/.nim/lib/system/avltree.nim:74:9: runtime error: member access within null pointer of type 'tyObject_AvlNode__IaqjtwKhxLEpvDS9bct9blEw' (aka 'struct tyObject_AvlNode__IaqjtwKhxLEpvDS9bct9blEw')
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /home/dian/.nim/lib/system/avltree.nim:74:9 in 
/home/dian/.nim/lib/system/avltree.nim:74:9: runtime error: applying zero offset to null pointer
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /home/dian/.nim/lib/system/avltree.nim:74:9 in 
/home/dian/.nim/lib/system/avltree.nim:74:9: runtime error: load of null pointer of type 'tyObject_AvlNode__IaqjtwKhxLEpvDS9bct9blEw *' (aka 'struct tyObject_AvlNode__IaqjtwKhxLEpvDS9bct9blEw *')
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /home/dian/.nim/lib/system/avltree.nim:74:9 in 
SIGSEGV: Illegal storage access. (Attempt to read from nil?)

==22360== Thread 16:
==22360== Invalid read of size 8
==22360==    at 0x402198: del__Io5JDKCS5u26IEWw0J53hQ (.nim/lib/system/avltree.nim:74)
==22360==    by 0x4024F6: rawDealloc__K7uQ6aTKvW6OnOV8EMoNNQ (.nim/lib/system/alloc.nim:870)
==22360==    by 0x4057B4: dealloc__Jg1OaY9ahkT3MBopLAXRSGw (.nim/lib/system/alloc.nim:971)
==22360==    by 0x4057B4: deallocSharedImpl__lmwgHsdhTsrQaepFju8wew (.nim/lib/system/alloc.nim:1086)
==22360==    by 0x4057B4: deallocShared (.nim/lib/system/memalloc.nim:295)
==22360==    by 0x4057B4: threadProcWrapper__oTnP9cUoE9cVTUL7iHAoIIAA (.nim/lib/system/threads.nim:193)
==22360==    by 0x49C8F26: start_thread (pthread_create.c:479)
==22360==    by 0x4ADDE0E: clone (clone.S:95)
==22360==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==22360== 
SIGSEGV: Illegal storage access. (Attempt to read from nil?)

Thread 3 "test2" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7ffff79e4700 (LWP 22569)]
0x0000000000402198 in del__Io5JDKCS5u26IEWw0J53hQ (a=0x40a118 <sharedHeap__R3bhvQCN0d6AYpkvxfT9aGw>, 
    t=0x40c9c0 <sharedHeap__R3bhvQCN0d6AYpkvxfT9aGw+10408>, x=140737349840928)
    at /home/dian/.nim/lib/system/avltree.nim:74
74        if isBottom(t): return
(gdb) bt
#0  0x0000000000402198 in del__Io5JDKCS5u26IEWw0J53hQ (a=0x40a118 <sharedHeap__R3bhvQCN0d6AYpkvxfT9aGw>, 
    t=0x40c9c0 <sharedHeap__R3bhvQCN0d6AYpkvxfT9aGw+10408>, x=140737349840928)
    at /home/dian/.nim/lib/system/avltree.nim:74
#1  0x00000000004024f7 in rawDealloc__K7uQ6aTKvW6OnOV8EMoNNQ (a=0x40a118 <sharedHeap__R3bhvQCN0d6AYpkvxfT9aGw>, 
    p=0x7ffff7be7040) at /home/dian/.nim/lib/system/alloc.nim:870
#2  0x00000000004057b5 in dealloc__Jg1OaY9ahkT3MBopLAXRSGw (
    allocator=0x40a118 <sharedHeap__R3bhvQCN0d6AYpkvxfT9aGw>, p=0x7ffff7be7040)
    at /home/dian/.nim/lib/system/alloc.nim:971
#3  deallocSharedImpl__lmwgHsdhTsrQaepFju8wew (p=0x7ffff7be7040) at /home/dian/.nim/lib/system/alloc.nim:1086
#4  deallocShared (p=0x7ffff7be7040) at /home/dian/.nim/lib/system/memalloc.nim:295
#5  threadProcWrapper__oTnP9cUoE9cVTUL7iHAoIIAA (closure=0x7ffff7be6068)
    at /home/dian/.nim/lib/system/threads.nim:193
#6  0x00007ffff7e38f27 in start_thread (arg=<optimized out>) at pthread_create.c:479
#7  0x00007ffff7d69e0f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

ghost · 2020-05-16T11:18:48Z

Nim Compiler Version 1.3.5 [Linux: amd64]
Compiled at 2020-05-16
Copyright (c) 2006-2020 by Andreas Rumpf

git hash: c777f2fb608e1f42daf31d314dda0050f6354acd
active boot switches: -d:release

ghost · 2020-06-12T09:59:34Z

Simplified example:

var threads: array[5, Thread[void]]

proc threadFn() {.thread.} =
  discard

proc main = 
  for i in 0 ..< 5:
    createThread(threads[i], threadFn)
  joinThreads(threads)

main()

ghost · 2020-06-12T10:07:44Z

With stacktrace:on hangs with this:

==26741== Thread 2:
==26741== Invalid read of size 8
==26741==    at 0x10BAD8: del__Io5JDKCS5u26IEWw0J53hQ (Things/Nim/lib/system/avltree.nim:74)
==26741==    by 0x10C6E4: rawDealloc__K7uQ6aTKvW6OnOV8EMoNNQ (Things/Nim/lib/system/alloc.nim:870)
==26741==    by 0x10CB1A: dealloc__Jg1OaY9ahkT3MBopLAXRSGw (Things/Nim/lib/system/alloc.nim:971)
==26741==    by 0x10CB7A: deallocSharedImpl__SAtZpVrJ3o5FJvSdLQe9auA (Things/Nim/lib/system/alloc.nim:1086)
==26741==    by 0x10CBA4: deallocShared (Things/Nim/lib/system/memalloc.nim:295)
==26741==    by 0x1143E2: threadProcWrapper__KwtUyNVh00QDWGRZcngjGA (Things/Nim/lib/system/threads.nim:193)
==26741==    by 0x49CE421: start_thread (in /usr/lib/libpthread-2.31.so)
==26741==    by 0x4AE6BF2: clone (in /usr/lib/libc-2.31.so)
==26741==  Address 0x0 is not stack'd, malloc'd or (recently) free'd

Without it crashes with:

==27864== Thread 5:
==27864== Invalid read of size 8
==27864==    at 0x10BA7B: del__Io5JDKCS5u26IEWw0J53hQ (Things/Nim/lib/system/avltree.nim:74)
==27864==    by 0x10C0AB: rawDealloc__K7uQ6aTKvW6OnOV8EMoNNQ (Things/Nim/lib/system/alloc.nim:870)
==27864==    by 0x10C13C: dealloc__Jg1OaY9ahkT3MBopLAXRSGw (Things/Nim/lib/system/alloc.nim:971)
==27864==    by 0x10C17A: deallocSharedImpl__SAtZpVrJ3o5FJvSdLQe9auA (Things/Nim/lib/system/alloc.nim:1086)
==27864==    by 0x10C1A4: deallocShared (Things/Nim/lib/system/memalloc.nim:295)
==27864==    by 0x1101F2: threadProcWrapper__KwtUyNVh00QDWGRZcngjGA (Things/Nim/lib/system/threads.nim:193)
==27864==    by 0x49CE421: start_thread (in /usr/lib/libpthread-2.31.so)
==27864==    by 0x4AE6BF2: clone (in /usr/lib/libc-2.31.so)
==27864==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==27864== 
SIGSEGV: Illegal storage access. (Attempt to read from nil?)
==27864== 
==27864== HEAP SUMMARY:
==27864==     in use at exit: 1,440 bytes in 5 blocks
==27864==   total heap usage: 5 allocs, 0 frees, 1,440 bytes allocated

Araq · 2020-06-16T10:00:09Z

For me this works

var threads: array[5, Thread[void]]

proc threadFn() {.thread.} =
  discard

proc main =
  for i in 0 ..< 5:
    createThread(threads[i], threadFn)
  joinThreads(threads)

main()

But I'm on Windows.

ghost · 2020-06-16T23:51:55Z

@Araq maybe we can add it as a test-case for ARC to see where it fails and where it works?

zacharycarter changed the title ~~SIGSEV encountered when creating threads in a loop~~ SIGSEV encountered when creating threads in a loop w/ --gc:arc Apr 9, 2020

mratsim added Garbage Collection Threads labels Apr 9, 2020

ghost mentioned this issue Apr 15, 2020

Spawn test fails to compile with gc:arc #13983

Closed

Araq added the ARC/ORC Memory Management label Apr 15, 2020

mratsim mentioned this issue Apr 22, 2020

Simple channels with --gc:arc #13936

Closed

Araq added the Showstopper label May 12, 2020

Araq closed this as completed in 79fe875 May 13, 2020

EchoPouet pushed a commit to EchoPouet/Nim that referenced this issue Jun 13, 2020

fixes nim-lang#13935

816693b

ghost mentioned this issue Jun 17, 2020

Add an ARC test with threads in a loop #14690

Closed

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SIGSEV encountered when creating threads in a loop w/ --gc:arc #13935

SIGSEV encountered when creating threads in a loop w/ --gc:arc #13935

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SIGSEV encountered when creating threads in a loop w/ --gc:arc #13935

SIGSEV encountered when creating threads in a loop w/ --gc:arc #13935

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zacharycarter commented Apr 9, 2020 • edited Loading

Example

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