зеркало из https://github.com/mozilla/gecko-dev.git
Bug 1651086 - Handle tgkill failure - r=canaltinova
On Linux (including Android), it was assumed that a registered thread could always be suspended through `tgkill`.
However in some cases a thread may not be correctly unregistered, in which case this would trigger `MOZ_ASSERT` or wait forever in the following loop.
This will especially be needed when `profiler_{,un}register_thread()` are made less strict in the following patch.
Windows and Mac already handle suspension failures.
Differential Revision: https://phabricator.services.mozilla.com/D83292
This commit is contained in:
Gerald Squelart
Родитель
760f059b00
Коммит
7610ff4326
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@ -329,66 +329,67 @@ void Sampler::SuspendAndSampleAndResumeThread(
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// Send message 1 to the samplee (the thread to be sampled), by
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// signalling at it.
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// This could fail if the thread doesn't exist anymore.
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int r = tgkill(mMyPid, sampleeTid, SIGPROF);
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MOZ_ASSERT(r == 0);
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// Wait for message 2 from the samplee, indicating that the context
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// is available and that the thread is suspended.
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while (true) {
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r = sem_wait(&sSigHandlerCoordinator->mMessage2);
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if (r == -1 && errno == EINTR) {
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// Interrupted by a signal. Try again.
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continue;
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if (r == 0) {
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// Wait for message 2 from the samplee, indicating that the context
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// is available and that the thread is suspended.
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while (true) {
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r = sem_wait(&sSigHandlerCoordinator->mMessage2);
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if (r == -1 && errno == EINTR) {
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// Interrupted by a signal. Try again.
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continue;
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}
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// We don't expect any other kind of failure.
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MOZ_ASSERT(r == 0);
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break;
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}
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// We don't expect any other kind of failure.
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//----------------------------------------------------------------//
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// Sample the target thread.
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// WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING
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//
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// The profiler's "critical section" begins here. In the critical section,
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// we must not do any dynamic memory allocation, nor try to acquire any lock
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// or any other unshareable resource. This is because the thread to be
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// sampled has been suspended at some entirely arbitrary point, and we have
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// no idea which unsharable resources (locks, essentially) it holds. So any
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// attempt to acquire any lock, including the implied locks used by the
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// malloc implementation, risks deadlock. This includes TimeStamp::Now(),
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// which gets a lock on Windows.
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// The samplee thread is now frozen and sSigHandlerCoordinator->mUContext is
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// valid. We can poke around in it and unwind its stack as we like.
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// Extract the current register values.
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Registers regs;
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PopulateRegsFromContext(regs, &sSigHandlerCoordinator->mUContext);
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aProcessRegs(regs, aNow);
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//----------------------------------------------------------------//
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// Resume the target thread.
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// Send message 3 to the samplee, which tells it to resume.
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r = sem_post(&sSigHandlerCoordinator->mMessage3);
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MOZ_ASSERT(r == 0);
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break;
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}
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//----------------------------------------------------------------//
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// Sample the target thread.
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// WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING
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//
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// The profiler's "critical section" begins here. In the critical section,
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// we must not do any dynamic memory allocation, nor try to acquire any lock
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// or any other unshareable resource. This is because the thread to be
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// sampled has been suspended at some entirely arbitrary point, and we have
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// no idea which unsharable resources (locks, essentially) it holds. So any
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// attempt to acquire any lock, including the implied locks used by the
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// malloc implementation, risks deadlock. This includes TimeStamp::Now(),
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// which gets a lock on Windows.
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// The samplee thread is now frozen and sSigHandlerCoordinator->mUContext is
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// valid. We can poke around in it and unwind its stack as we like.
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// Extract the current register values.
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Registers regs;
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PopulateRegsFromContext(regs, &sSigHandlerCoordinator->mUContext);
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aProcessRegs(regs, aNow);
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//----------------------------------------------------------------//
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// Resume the target thread.
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// Send message 3 to the samplee, which tells it to resume.
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r = sem_post(&sSigHandlerCoordinator->mMessage3);
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MOZ_ASSERT(r == 0);
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// Wait for message 4 from the samplee, which tells us that it has
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// finished with |sSigHandlerCoordinator|.
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while (true) {
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r = sem_wait(&sSigHandlerCoordinator->mMessage4);
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if (r == -1 && errno == EINTR) {
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continue;
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// Wait for message 4 from the samplee, which tells us that it has
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// finished with |sSigHandlerCoordinator|.
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while (true) {
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r = sem_wait(&sSigHandlerCoordinator->mMessage4);
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if (r == -1 && errno == EINTR) {
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continue;
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}
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MOZ_ASSERT(r == 0);
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break;
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}
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MOZ_ASSERT(r == 0);
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break;
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}
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// The profiler's critical section ends here. After this point, none of the
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// critical section limitations documented above apply.
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//
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// WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING
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// The profiler's critical section ends here. After this point, none of the
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// critical section limitations documented above apply.
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//
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// WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING
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}
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// This isn't strictly necessary, but doing so does help pick up anomalies
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// in which the signal handler is running when it shouldn't be.
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@ -323,66 +323,67 @@ void Sampler::SuspendAndSampleAndResumeThread(
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// Send message 1 to the samplee (the thread to be sampled), by
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// signalling at it.
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// This could fail if the thread doesn't exist anymore.
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int r = tgkill(mMyPid, sampleeTid, SIGPROF);
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MOZ_ASSERT(r == 0);
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// Wait for message 2 from the samplee, indicating that the context
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// is available and that the thread is suspended.
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while (true) {
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r = sem_wait(&sSigHandlerCoordinator->mMessage2);
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if (r == -1 && errno == EINTR) {
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// Interrupted by a signal. Try again.
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continue;
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if (r == 0) {
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// Wait for message 2 from the samplee, indicating that the context
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// is available and that the thread is suspended.
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while (true) {
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r = sem_wait(&sSigHandlerCoordinator->mMessage2);
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if (r == -1 && errno == EINTR) {
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// Interrupted by a signal. Try again.
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continue;
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}
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// We don't expect any other kind of failure.
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MOZ_ASSERT(r == 0);
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break;
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}
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// We don't expect any other kind of failure.
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//----------------------------------------------------------------//
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// Sample the target thread.
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// WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING
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//
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// The profiler's "critical section" begins here. In the critical section,
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// we must not do any dynamic memory allocation, nor try to acquire any lock
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// or any other unshareable resource. This is because the thread to be
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// sampled has been suspended at some entirely arbitrary point, and we have
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// no idea which unsharable resources (locks, essentially) it holds. So any
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// attempt to acquire any lock, including the implied locks used by the
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// malloc implementation, risks deadlock. This includes TimeStamp::Now(),
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// which gets a lock on Windows.
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// The samplee thread is now frozen and sSigHandlerCoordinator->mUContext is
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// valid. We can poke around in it and unwind its stack as we like.
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// Extract the current register values.
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Registers regs;
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PopulateRegsFromContext(regs, &sSigHandlerCoordinator->mUContext);
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aProcessRegs(regs, aNow);
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//----------------------------------------------------------------//
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// Resume the target thread.
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// Send message 3 to the samplee, which tells it to resume.
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r = sem_post(&sSigHandlerCoordinator->mMessage3);
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MOZ_ASSERT(r == 0);
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break;
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}
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//----------------------------------------------------------------//
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// Sample the target thread.
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// WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING
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//
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// The profiler's "critical section" begins here. In the critical section,
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// we must not do any dynamic memory allocation, nor try to acquire any lock
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// or any other unshareable resource. This is because the thread to be
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// sampled has been suspended at some entirely arbitrary point, and we have
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// no idea which unsharable resources (locks, essentially) it holds. So any
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// attempt to acquire any lock, including the implied locks used by the
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// malloc implementation, risks deadlock. This includes TimeStamp::Now(),
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// which gets a lock on Windows.
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// The samplee thread is now frozen and sSigHandlerCoordinator->mUContext is
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// valid. We can poke around in it and unwind its stack as we like.
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// Extract the current register values.
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Registers regs;
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PopulateRegsFromContext(regs, &sSigHandlerCoordinator->mUContext);
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aProcessRegs(regs, aNow);
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//----------------------------------------------------------------//
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// Resume the target thread.
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// Send message 3 to the samplee, which tells it to resume.
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r = sem_post(&sSigHandlerCoordinator->mMessage3);
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MOZ_ASSERT(r == 0);
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// Wait for message 4 from the samplee, which tells us that it has
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// finished with |sSigHandlerCoordinator|.
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while (true) {
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r = sem_wait(&sSigHandlerCoordinator->mMessage4);
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if (r == -1 && errno == EINTR) {
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continue;
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// Wait for message 4 from the samplee, which tells us that it has
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// finished with |sSigHandlerCoordinator|.
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while (true) {
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r = sem_wait(&sSigHandlerCoordinator->mMessage4);
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if (r == -1 && errno == EINTR) {
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continue;
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}
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MOZ_ASSERT(r == 0);
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break;
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}
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MOZ_ASSERT(r == 0);
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break;
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}
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// The profiler's critical section ends here. After this point, none of the
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// critical section limitations documented above apply.
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//
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// WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING
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// The profiler's critical section ends here. After this point, none of the
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// critical section limitations documented above apply.
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//
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// WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING
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}
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// This isn't strictly necessary, but doing so does help pick up anomalies
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// in which the signal handler is running when it shouldn't be.
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