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SharedBuffer: Amend commit 2d4d465206

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I had the right cause of the SharedBuffer leak, but goofed the fix by
desynching the per-pid refcount and the global refcount.

Fix that, and add a generous sprinkle of asserts to make sure the two
stay in sync.

Fixes #341

(... for real this time)
This commit is contained in:
Robin Burchell 2019-07-19 23:14:56 +02:00 • committed by Andreas Kling
parent 253e391bfc
commit 56217c7432
2 changed files with 29 additions and 1 deletions
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29
Kernel/SharedBuffer.cpp
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@ -9,6 +9,23 @@ Lockable<HashMap<int, OwnPtr<SharedBuffer>>>& shared_buffers()
return *map;
}
void SharedBuffer::sanity_check(const char* what)
{
LOCKER(shared_buffers().lock());
unsigned found_refs = 0;
for (const auto& ref : m_refs)
found_refs += ref.count;
if (found_refs != m_total_refs) {
dbgprintf("%s sanity -- SharedBuffer{%p} id: %d has total refs %d but we found %d\n", what, this, m_shared_buffer_id, m_total_refs, found_refs);
for (const auto& ref : m_refs) {
dbgprintf(" ref from pid %d: refcnt %d\n", ref.pid, ref.count);
}
ASSERT_NOT_REACHED();
}
}
bool SharedBuffer::is_shared_with(pid_t peer_pid)
{
LOCKER(shared_buffers().lock());
@ -33,6 +50,7 @@ void* SharedBuffer::ref_for_process_and_get_address(Process& process)
ref.region = process.allocate_region_with_vmo(VirtualAddress(), size(), m_vmo, 0, "SharedBuffer", PROT_READ | (m_writable ? PROT_WRITE : 0));
ref.region->set_shared(true);
}
sanity_check("ref_for_process_and_get_address");
return ref.region->vaddr().as_ptr();
}
}
@ -45,11 +63,13 @@ void SharedBuffer::share_with(pid_t peer_pid)
for (auto& ref : m_refs) {
if (ref.pid == peer_pid) {
// don't increment the reference count yet; let them get_shared_buffer it first.
sanity_check("share_with (old ref)");
return;
}
}
m_refs.append(Reference(peer_pid));
sanity_check("share_with (new ref)");
}
void SharedBuffer::deref_for_process(Process& process)
@ -58,7 +78,9 @@ void SharedBuffer::deref_for_process(Process& process)
for (int i = 0; i < m_refs.size(); ++i) {
auto& ref = m_refs[i];
if (ref.pid == process.pid()) {
if (--ref.count == 0) {
ref.count--;
m_total_refs--;
if (ref.count == 0) {
#ifdef SHARED_BUFFER_DEBUG
dbgprintf("Releasing shared buffer reference on %d of size %d by PID %d\n", m_shared_buffer_id, size(), process.pid());
#endif
@ -67,11 +89,14 @@ void SharedBuffer::deref_for_process(Process& process)
#ifdef SHARED_BUFFER_DEBUG
dbgprintf("Released shared buffer reference on %d of size %d by PID %d\n", m_shared_buffer_id, size(), process.pid());
#endif
sanity_check("deref_for_process");
destroy_if_unused();
return;
}
}
}
ASSERT_NOT_REACHED();
}
void SharedBuffer::disown(pid_t pid)
@ -83,6 +108,7 @@ void SharedBuffer::disown(pid_t pid)
#ifdef SHARED_BUFFER_DEBUG
dbgprintf("Disowning shared buffer %d of size %d by PID %d\n", m_shared_buffer_id, size(), pid);
#endif
m_total_refs -= ref.count;
m_refs.remove(i);
#ifdef SHARED_BUFFER_DEBUG
dbgprintf("Disowned shared buffer %d of size %d by PID %d\n", m_shared_buffer_id, size(), pid);
@ -96,6 +122,7 @@ void SharedBuffer::disown(pid_t pid)
void SharedBuffer::destroy_if_unused()
{
LOCKER(shared_buffers().lock());
sanity_check("destroy_if_unused");
if (m_total_refs == 0) {
#ifdef SHARED_BUFFER_DEBUG
kprintf("Destroying unused SharedBuffer{%p} id: %d\n", this, m_shared_buffer_id);