[Bug 237195] pthread_mutex_unlock crash as unlocked mutex destroyed by signaled thread
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bugzilla-noreply at freebsd.org
Thu Apr 11 09:12:11 UTC 2019
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=237195
Bug ID: 237195
Summary: pthread_mutex_unlock crash as unlocked mutex destroyed
by signaled thread
Product: Base System
Version: 12.0-RELEASE
Hardware: amd64
OS: Any
Status: New
Severity: Affects Many People
Priority: ---
Component: threads
Assignee: threads at FreeBSD.org
Reporter: freebsd at hurrikhan.eu
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A simple program to reproduce the issue.
I have this program where N threads are communicating with one thread through
messages.
Some of theses messages are used to ensure synchronisation (e.g.: flush).
Each messsage contain a mutex and a condition.
When testing on FreeBSD 12.0, the program randomly crashed.
Every clue was saying the mutex was destroyed while being unlocked.
Given said program is pretty huge, I've written a small, simplified, code with
similar behaviour and it crashed the same way.
#0 0x000000080065c93a in ?? () from /lib/libthr.so.3
#1 0x0000000000401dd8 in mcv_progress (mcv=0x801c1ac00) at mutex_test.c:365
(calling pthread_mutex_unlock)
#2 0x0000000000401f46 in read_thread (arg=0x7fffffffdac0) at mutex_test.c:412
#3 0x0000000800654776 in ?? () from /lib/libthr.so.3
I suspect what happens looks something like this:
client/writer server/reader
1) queues message
2) locks message.mutex 1) dequeues message
2) process message
3) waits for message.condition
3) locks message.mutex
4) signals message.condition
4) unlocks message.mutex 5) unlocks message.mutex
5) destroy message memory 6) somehow, still in pthread_mutex_unlock after
the client got the hand back, maybe accesses
6) frees message memory mutex content and crashes as it has been
trashed
The same program works fine under any load and parameters on several Linux
versions and OSX 10.14.4.
If this hypothesis verifies, I suppose it only affects programs rapidly
creating and destroying mutexes(+conditions?).
Please find attached the test program.
To reproduce the issue, I ctrl-C the program after 5 seconds if it didn't crash
and restart it immediately. Four or five tries of this are usually enough.
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