iocp: fix crash, GetQueuedCompletionStatus() write freed WSAOVERLAPPED memory

[jimying]

try to fix issue #985

[nanangizz]

Great! I assume you've tested this and it does fix the issue :)

I think we also need to run under somekind of stress test, e.g: using ioqueue test in pjlib-test, to make sure all memory pools (of pending ops) are properly released. Note that the after an ioqueue key is unregistered, the key will be put into the closing-key-list and soon into the free-key-list to be reused by another socket. We need to make sure that all pending op has been freed before the key is freed & reused.

Next, perhaps we can apply a little bit optimization, e.g: instead of mem-pool for each pending-op, perhaps mem-pool per ioqueue-key to avoid multiple alloc+free for multiple pending-op, using same mechanism as ioqueue key (employing additional list for keeping unused pending-op instances to be reused later).

[jimying]

Note:
this only fix the issue when PJ_IOQUEUE_HAS_SAFE_UNREG=1;
PJ_IOQUEUE_HAS_SAFE_UNREG=0 still has memory error

[nanangizz]

Note: this only fix the issue when PJ_IOQUEUE_HAS_SAFE_UNREG=1; PJ_IOQUEUE_HAS_SAFE_UNREG=0 still has memory error

When PJ_IOQUEUE_HAS_SAFE_UNREG==1, the key won't be reused for 500ms (configurable via PJ_IOQUEUE_KEY_FREE_DELAY), this is a bit risky actually, e.g: on high CPU load, the cancellation may take longer?

[nanangizz]

Tried to run pjlib-test with this PR patch on VS2005 and pool debugging enabled (so pool uses normal malloc/free(), by setting PJ_POOL_DEBUG to 1 in config_site.h), I got an assertion:

 	_wassert(const wchar_t * expr=0x004d1e90, const wchar_t * filename=0x004d1cf0, unsigned int lineno=588) Line 212	C
 	pj_ioqueue_register_sock2(pj_pool_t * pool=0x023a29b8, pj_ioqueue_t * ioqueue=0x023a2a2c, long sock=388, pj_grp_lock_t * grp_lock=0x00000000, void * user_data=0x00000002, const pj_ioqueue_callback * cb=0x0019fb54, pj_ioqueue_key_t * * key=0x0019fbec) Line 588 + 0x2c bytes	C
 	pj_ioqueue_register_sock(pj_pool_t * pool=0x023a29b8, pj_ioqueue_t * ioqueue=0x023a2a2c, long sock=388, void * user_data=0x00000002, const pj_ioqueue_callback * cb=0x0019fb54, pj_ioqueue_key_t * * key=0x0019fbec) Line 665 + 0x1f bytes	C
 	unregister_test(const pj_ioqueue_cfg * cfg=0x0019fd34) Line 554 + 0x23 bytes	C
 	udp_ioqueue_test_imp(const pj_ioqueue_cfg * cfg=0x0019fd34) Line 1190 + 0x9 bytes	C
 	udp_ioqueue_test() Line 1255 + 0x9 bytes	C
 	test_inner() Line 171 + 0x2a bytes	C
 	test_main() Line 245 + 0x5 bytes	C

Not sure if this is the same issue, but this assertion does not happen when using ioqueue select.

[jimying]

@nanangizz no this patch, Is there this assert?

[nanangizz]

@nanangizz no this patch, Is there this assert?

Yes, same assert without this patch.

[jimying]

Tried to run pjlib-test with this PR patch on VS2005 and pool debugging enabled (so pool uses normal malloc/free(), by setting PJ_POOL_DEBUG to 1 in config_site.h), I got an assertion:

 	_wassert(const wchar_t * expr=0x004d1e90, const wchar_t * filename=0x004d1cf0, unsigned int lineno=588) Line 212	C
 	pj_ioqueue_register_sock2(pj_pool_t * pool=0x023a29b8, pj_ioqueue_t * ioqueue=0x023a2a2c, long sock=388, pj_grp_lock_t * grp_lock=0x00000000, void * user_data=0x00000002, const pj_ioqueue_callback * cb=0x0019fb54, pj_ioqueue_key_t * * key=0x0019fbec) Line 588 + 0x2c bytes	C
 	pj_ioqueue_register_sock(pj_pool_t * pool=0x023a29b8, pj_ioqueue_t * ioqueue=0x023a2a2c, long sock=388, void * user_data=0x00000002, const pj_ioqueue_callback * cb=0x0019fb54, pj_ioqueue_key_t * * key=0x0019fbec) Line 665 + 0x1f bytes	C
 	unregister_test(const pj_ioqueue_cfg * cfg=0x0019fd34) Line 554 + 0x23 bytes	C
 	udp_ioqueue_test_imp(const pj_ioqueue_cfg * cfg=0x0019fd34) Line 1190 + 0x9 bytes	C
 	udp_ioqueue_test() Line 1255 + 0x9 bytes	C
 	test_inner() Line 171 + 0x2a bytes	C
 	test_main() Line 245 + 0x5 bytes	C

Not sure if this is the same issue, but this assertion does not happen when using ioqueue select.

I found the reason: key double unregister.
Fixed: when key->closing = 1, not unregister.
now test passed.

[nanangizz]

Thanks @jimying .

Honestly I haven't got a chance to reproduce the original issue and test the proposed solution. I believe you are using this ioqueue in real world, experienced the issue, and find this solution does work, is that correct?

Next, here are few notes about the proposed solution:

• As you've mentioned, the approach requires PJ_IOQUEUE_HAS_SAFE_UNREG to work, so I think this mode has to be enforced somehow.
• Also as I've mentioned before, the safe key unregistration relies on timer (default is 500ms), there is a risk when CPU load is high, increasing the timeout is not ideal as the risk itself is actually still there, only reduced to some degree. Perhaps the unregistration should rely on zero-pending-operation instead, or combination of them somehow.
• Memory pool per operation can be optimized. Note that a single ioqueue key can have many & rapid operations, e.g: receiving RTP packets, so creating & releasing pool for each operation does not sound very optimized. An idea is to have some pool of pending_op (just like pool of key), may be owned by ioqueue or by key.

Also, this ioqueue has been disabled for quite sometime and some improvement in the ioqueue area may not be integrated into this ioqueue, e.g: group lock for key. So please understand that there may still be some steps required to enable this ioqueue again :)

[jimying]

@nanangizz i write a simple demo to reproduce the crash issue in msys2, #4172

I have tested it, in old code, it can 100% reproduce the crash.

To test new code we can git cherry-pick the demo patch to this branch.

[nanangizz]

Thanks @jimying.

[sauwming]

Hi @jimying, please let us know whether you plan to incorporate @nanangizz suggestions above.
In my opinion, the first two (enforcingPJ_IOQUEUE_HAS_SAFE_UNREG and zero pending-op) are important and shouldn't require much modification.
While for the last suggestion (memory pool), I think it's optional if you don't have the time necessary to implement it. Just put a note in the code for future optimisation.

[jimying]

@sauwming sorry, I will submit it as soon as possible today or tomorrow

[jimying]

enforcingPJ_IOQUEUE_HAS_SAFE_UNREG and zero pending-op

new commits do:

1. remove macro PJ_IOQUEUE_HAS_SAFE_UNREG, only keep PJ_IOQUEUE_HAS_SAFE_UNREG=1 logic
2. remove closing_list, when ref_count=0 return key to freelist.
   In order to achieve，add ref when alloc pending-op and dec ref when free it