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[PLAT-6112] Fix possible deadlock when recording threads #1011

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Feb 23, 2021
Merged

[PLAT-6112] Fix possible deadlock when recording threads #1011

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36 changes: 17 additions & 19 deletions Bugsnag/Payload/BugsnagThread+Recording.m
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Original file line number Diff line number Diff line change
Expand Up @@ -32,34 +32,33 @@ static void backtrace_for_thread(thread_t thread, struct backtrace_t *output) {
}
}

static void backtrace_for_callstack(NSArray<NSNumber *> *callStackReturnAddresses, struct backtrace_t *output) {
output->length = (int)MIN(callStackReturnAddresses.count, kMaxAddresses);
for (int i = 0; i < output->length; i++) {
output->addresses[i] = (uintptr_t)callStackReturnAddresses[i].unsignedLongLongValue;
}
}


// MARK: -

@implementation BugsnagThread (Recording)

+ (NSArray<BugsnagThread *> *)allThreads:(BOOL)allThreads callStackReturnAddresses:(NSArray<NSNumber *> *)callStackReturnAddresses {
struct backtrace_t backtrace;
backtrace.length = (int)MIN(callStackReturnAddresses.count, kMaxAddresses);
for (int i = 0; i < backtrace.length; i++) {
backtrace.addresses[i] = (uintptr_t)callStackReturnAddresses[i].unsignedLongLongValue;
}
if (allThreads) {
return [BugsnagThread allThreadsWithCallStackReturnAddresses:callStackReturnAddresses];
return [BugsnagThread allThreadsWithCurrentThreadBacktrace:&backtrace];
} else {
return @[[BugsnagThread currentThreadWithCallStackReturnAddresses:callStackReturnAddresses]];
return @[[BugsnagThread currentThreadWithBacktrace:&backtrace]];
}
}

+ (NSArray<BugsnagThread *> *)allThreadsWithCallStackReturnAddresses:(NSArray<NSNumber *> *)callStackReturnAddresses {
+ (NSArray<BugsnagThread *> *)allThreadsWithCurrentThreadBacktrace:(struct backtrace_t *)currentThreadBacktrace {
thread_t *threads = NULL;
mach_msg_type_number_t threadCount = 0;

bsg_kscrashsentry_suspend_threads_user();

// While threads are suspended only async-signal-safe functions should be used,
// as another threads may have been suspended while holding a lock.
// as another threads may have been suspended while holding a lock in malloc,
// the Objective-C runtime, or other subsystems.

if (task_threads(mach_task_self(), &threads, &threadCount) != KERN_SUCCESS) {
bsg_kscrashsentry_resume_threads_user(false);
Expand All @@ -71,7 +70,7 @@ @implementation BugsnagThread (Recording)
for (int i = 0; i < threadCount; i++) {
BOOL isCurrentThread = MACH_PORT_INDEX(threads[i]) == MACH_PORT_INDEX(bsg_ksmachthread_self());
if (isCurrentThread) {
backtrace_for_callstack(callStackReturnAddresses, &backtraces[i]);
backtraces[i].length = 0; // currentThreadBacktrace will be used instead
} else {
backtrace_for_thread(threads[i], &backtraces[i]);
}
Expand All @@ -83,9 +82,10 @@ @implementation BugsnagThread (Recording)

for (int i = 0; i < threadCount; i++) {
BOOL isCurrentThread = MACH_PORT_INDEX(threads[i]) == MACH_PORT_INDEX(bsg_ksmachthread_self());
struct backtrace_t *backtrace = isCurrentThread ? currentThreadBacktrace : &backtraces[i];
[objects addObject:[[BugsnagThread alloc] initWithMachThread:threads[i]
backtraceAddresses:backtraces[i].addresses
backtraceLength:backtraces[i].length
backtraceAddresses:backtrace->addresses
backtraceLength:backtrace->length
errorReportingThread:isCurrentThread
index:i]];
}
Expand All @@ -98,10 +98,8 @@ @implementation BugsnagThread (Recording)
return objects;
}

+ (instancetype)currentThreadWithCallStackReturnAddresses:(NSArray<NSNumber *> *)callStackReturnAddresses {
+ (instancetype)currentThreadWithBacktrace:(struct backtrace_t *)backtrace {
thread_t thread = mach_thread_self();
struct backtrace_t backtrace;
backtrace_for_callstack(callStackReturnAddresses, &backtrace);
thread_t *threads = NULL;
mach_msg_type_number_t threadCount = 0;
int threadIndex = 0;
Expand All @@ -115,8 +113,8 @@ + (instancetype)currentThreadWithCallStackReturnAddresses:(NSArray<NSNumber *> *
vm_deallocate(mach_task_self(), (vm_address_t)threads, sizeof(thread_t) * threadCount);
}
BugsnagThread *object = [[BugsnagThread alloc] initWithMachThread:thread
backtraceAddresses:backtrace.addresses
backtraceLength:backtrace.length
backtraceAddresses:backtrace->addresses
backtraceLength:backtrace->length
errorReportingThread:YES
index:threadIndex];
mach_port_deallocate(mach_task_self(), thread);
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3 changes: 3 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -5,6 +5,9 @@ Changelog

### Bug fixes

* Fix possible deadlock when recording thread information for handled errors.
[1011](https://github.com/bugsnag/bugsnag-cocoa/pull/1011)

* Fix Swift 5.4 fatal error message parsing.
[1010](https://github.com/bugsnag/bugsnag-cocoa/pull/1010)

Expand Down