Bug 1304106
Summary: | dlopen deadlocks during thread cancellation | ||||||
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Product: | Red Hat Enterprise Linux 6 | Reporter: | Anit Lulla <alulla> | ||||
Component: | glibc | Assignee: | glibc team <glibc-bugzilla> | ||||
Status: | CLOSED WONTFIX | QA Contact: | qe-baseos-tools-bugs | ||||
Severity: | unspecified | Docs Contact: | |||||
Priority: | unspecified | ||||||
Version: | 6.9 | CC: | ashankar, codonell, fweimer, mnewsome, pfrankli | ||||
Target Milestone: | rc | ||||||
Target Release: | --- | ||||||
Hardware: | Unspecified | ||||||
OS: | Unspecified | ||||||
Whiteboard: | |||||||
Fixed In Version: | Doc Type: | If docs needed, set a value | |||||
Doc Text: | Story Points: | --- | |||||
Clone Of: | Environment: | ||||||
Last Closed: | 2017-08-29 20:27:21 UTC | Type: | Bug | ||||
Regression: | --- | Mount Type: | --- | ||||
Documentation: | --- | CRM: | |||||
Verified Versions: | Category: | --- | |||||
oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |||||
Cloudforms Team: | --- | Target Upstream Version: | |||||
Embargoed: | |||||||
Attachments: |
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I'm moving this to rhel-6.10 for review. We aren't going to look at this for rhel-6.9. There are several cases which we have fixed where the error paths out of dlopen failed to successfully rollback the changes for intermediate loads, but it's likely we haven't done this for all the cases possible. It would be interesting if this reproduces in upstream master. Constructors are foreign function calls which happen while the dynamic loader is loading the shared library, as such, there are some things which don't work during this particular stage of loading. In this case the foreign function has triggered deferred cancellation and has left the internal dynamic loader locks taken. One fix would be to push a cleanup function in dlopen which releases the locks if the foreign functions call a cancellation point. Unfortunately this kind of fix is invasive for RHEL6, and upstream still doesn't pass this test. I've opened upstream bug 22034 for this to be tracked upstream. |
Created attachment 1120575 [details] C++ source code that reproduces the bug Description of problem: dlopen() deadlocks when a prior dlopen() call is cancelled via pthread_cancel() Version-Release number of selected component (if applicable): All versions How reproducible: Always (see reproducer, which is attached) #include <iostream> #include <unistd.h> #include <pthread.h> #include <dlfcn.h> using namespace std; // to reproduce (copy contents to dl_deadlock.cpp) // // $ g++ -D FOO_SHARE_LIB -shared -o libfoo.so -fPIC dl_deadlock.cpp // $ g++ -g dl_deadlock.cpp -ldl -lpthread // $ ./a.out #ifdef FOO_SHARE_LIB class Foo { public: Foo() { cout << "construct foo" << endl; usleep(500000); cout << "done construct foo" << endl; } }; Foo g_foo; #else extern "C" void *thrfxn_init(void *arg) { usleep(500000); return NULL; } extern "C" void *thrfxn(void *arg) { cout << "before dlopen" << endl; void *h = dlopen("./libfoo.so", RTLD_GLOBAL | RTLD_NOW); cout << "after dlopen" << endl; if (h); dlclose(h); } int main() { pthread_t thr; // need to call cancel so pthread_cancel_init is called, // which calls into libdl (needed since first pthread_cancel waits on dlopen) pthread_create(&thr, NULL, thrfxn_init, NULL); pthread_cancel(thr); pthread_join(thr, NULL); cout << "before thread create" << endl; pthread_create(&thr, NULL, thrfxn, NULL); cout << "after thread create" << endl; // sleep 5ms usleep(5000); // cancel thread that is waiting in dlopen cout << "before cancel" << endl; pthread_cancel(thr); cout << "after cancel" << endl; // this dlopen will now deadlock void *h = dlopen("/lib64/libc.so.6", RTLD_GLOBAL | RTLD_NOW); if (h) dlclose(h); //find_symbol("PA_REPORT_CALC_DISPATCH", PA_REPORT_CALC_DISPATCH); //FDSA_FQL_SERVICE, CREATE_FDSA_FQL_SERVICE; cout << "before join" << endl; pthread_join(thr, NULL); cout << "after join" << endl; return 0; } #endif Steps to Reproduce: 1. g++ -D FOO_SHARE_LIB -shared -o libfoo.so -fPIC dl_deadlock.cpp 2. g++ -g dl_deadlock.cpp -ldl -lpthread 3. ./a.out Actual results: before thread create after thread create before dlopen construct foo before cancel after cancel -- deadlock -- Expected results: before thread create after thread create before dlopen construct foo before cancel after cancel done construct foo after dlopen before join -- program completion -- Additional info: