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Kernel: Use consistent lock acquisition order in Thread::block*()

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We want to grab g_scheduler_lock *before* Thread::m_block_lock.
This appears to have fixed a deadlock that I encountered while building
DOOM with make -j2.
This commit is contained in:
Andreas Kling 2022-08-17 20:14:49 +02:00
parent ae8558dd5c
commit ec330c2ce6
1 changed files with 4 additions and 3 deletions
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7
Kernel/Thread.cpp
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@ -155,6 +155,8 @@ Thread::BlockResult Thread::block_impl(BlockTimeout const& timeout, Blocker& blo
ScopedCritical critical;
VERIFY(!Memory::s_mm_lock.is_locked_by_current_processor());
SpinlockLocker scheduler_lock(g_scheduler_lock);
SpinlockLocker block_lock(m_block_lock);
// We need to hold m_block_lock so that nobody can unblock a blocker as soon
// as it is constructed and registered elsewhere
@ -168,7 +170,6 @@ Thread::BlockResult Thread::block_impl(BlockTimeout const& timeout, Blocker& blo
return BlockResult::NotBlocked;
}
SpinlockLocker scheduler_lock(g_scheduler_lock);
// Relaxed semantics are fine for timeout_unblocked because we
// synchronize on the spin locks already.
Atomic<bool, AK::MemoryOrder::memory_order_relaxed> timeout_unblocked(false);
@ -212,8 +213,8 @@ Thread::BlockResult Thread::block_impl(BlockTimeout const& timeout, Blocker& blo
set_state(Thread::State::Blocked);
scheduler_lock.unlock();
block_lock.unlock();
scheduler_lock.unlock();
dbgln_if(THREAD_DEBUG, "Thread {} blocking on {} ({}) -->", *this, &blocker, blocker.state_string());
bool did_timeout = false;
@ -296,8 +297,8 @@ void Thread::block(Kernel::Mutex& lock, SpinlockLocker<Spinlock>& lock_lock, u32
set_state(Thread::State::Blocked);
scheduler_lock.unlock();
block_lock.unlock();
scheduler_lock.unlock();
lock_lock.unlock();