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Kernel: Simplify ProcFS generated buffer caching

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Use a Mutex instead of a SpinLock to protect the per-FileDescription
generated data cache. This allows processes to go to sleep while
waiting their turn.

Also don't try to be clever by reusing existing cache buffers.
Just allocate KBuffers as needed (and make sure to surface failures.)
This commit is contained in:
Andreas Kling 2021-07-20 14:43:15 +02:00
parent 4d2473b7fa
commit a3063dfd33
Notes: sideshowbarker 2024-07-18 08:40:49 +09:00 
Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/a3063dfd337
2 changed files with 28 additions and 37 deletions
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61
Kernel/ProcessExposed.cpp
View file

@ -69,7 +69,7 @@ ProcFSExposedLink::ProcFSExposedLink(StringView name, InodeIndex preallocated_in
}
struct ProcFSInodeData : public FileDescriptionData {
RefPtr<KBufferImpl> buffer;
OwnPtr<KBuffer> buffer;
};
KResultOr<size_t> ProcFSGlobalInformation::read_bytes(off_t offset, size_t count, UserOrKernelBuffer& buffer, FileDescription* description) const
@ -81,13 +81,16 @@ KResultOr<size_t> ProcFSGlobalInformation::read_bytes(off_t offset, size_t count
if (!description)
return KResult(EIO);
MutexLocker locker(m_refresh_lock);
if (!description->data()) {
dbgln("ProcFSGlobalInformation: Do not have cached data!");
return KResult(EIO);
}
// Be sure to keep a reference to data_buffer while we use it!
RefPtr<KBufferImpl> data_buffer = static_cast<ProcFSInodeData&>(*description->data()).buffer;
auto& typed_cached_data = static_cast<ProcFSInodeData&>(*description->data());
auto& data_buffer = typed_cached_data.buffer;
if (!data_buffer || (size_t)offset >= data_buffer->size())
return 0;
@ -101,26 +104,19 @@ KResultOr<size_t> ProcFSGlobalInformation::read_bytes(off_t offset, size_t count
KResult ProcFSGlobalInformation::refresh_data(FileDescription& description) const
{
ScopedSpinLock lock(m_refresh_lock);
MutexLocker lock(m_refresh_lock);
auto& cached_data = description.data();
if (!cached_data)
if (!cached_data) {
cached_data = adopt_own_if_nonnull(new (nothrow) ProcFSInodeData);
VERIFY(description.data());
auto& buffer = static_cast<ProcFSInodeData&>(*cached_data).buffer;
if (buffer) {
// If we're reusing the buffer, reset the size to 0 first. This
// ensures we don't accidentally leak previously written data.
buffer->set_size(0);
if (!cached_data)
return ENOMEM;
}
KBufferBuilder builder(buffer, true);
KBufferBuilder builder;
if (!const_cast<ProcFSGlobalInformation&>(*this).output(builder))
return ENOENT;
// We don't use builder.build() here, which would steal our buffer
// and turn it into an OwnPtr. Instead, just flush to the buffer so
// that we can read all the data that was written.
if (!builder.flush())
return ENOMEM;
if (!buffer)
auto& typed_cached_data = static_cast<ProcFSInodeData&>(*cached_data);
typed_cached_data.buffer = builder.build();
if (!typed_cached_data.buffer)
return ENOMEM;
return KSuccess;
}
@ -139,8 +135,10 @@ KResultOr<size_t> ProcFSProcessInformation::read_bytes(off_t offset, size_t coun
return KResult(EIO);
}
// Be sure to keep a reference to data_buffer while we use it!
RefPtr<KBufferImpl> data_buffer = static_cast<ProcFSInodeData&>(*description->data()).buffer;
MutexLocker locker(m_refresh_lock);
auto& typed_cached_data = static_cast<ProcFSInodeData&>(*description->data());
auto& data_buffer = typed_cached_data.buffer;
if (!data_buffer || (size_t)offset >= data_buffer->size())
return 0;
@ -171,26 +169,19 @@ KResult ProcFSProcessInformation::refresh_data(FileDescription& description) con
ScopeGuard guard = [&] {
process->ptrace_lock().unlock();
};
ScopedSpinLock lock(m_refresh_lock);
MutexLocker locker(m_refresh_lock);
auto& cached_data = description.data();
if (!cached_data)
if (!cached_data) {
cached_data = adopt_own_if_nonnull(new (nothrow) ProcFSInodeData);
VERIFY(description.data());
auto& buffer = static_cast<ProcFSInodeData&>(*cached_data).buffer;
if (buffer) {
// If we're reusing the buffer, reset the size to 0 first. This
// ensures we don't accidentally leak previously written data.
buffer->set_size(0);
if (!cached_data)
return ENOMEM;
}
KBufferBuilder builder(buffer, true);
KBufferBuilder builder;
if (!const_cast<ProcFSProcessInformation&>(*this).output(builder))
return ENOENT;
// We don't use builder.build() here, which would steal our buffer
// and turn it into an OwnPtr. Instead, just flush to the buffer so
// that we can read all the data that was written.
if (!builder.flush())
return ENOMEM;
if (!buffer)
auto& typed_cached_data = static_cast<ProcFSInodeData&>(*cached_data);
typed_cached_data.buffer = builder.build();
if (!typed_cached_data.buffer)
return ENOMEM;
return KSuccess;
}

4
Kernel/ProcessExposed.h
View file

@ -187,7 +187,7 @@ protected:
virtual KResult refresh_data(FileDescription&) const override;
virtual bool output(KBufferBuilder& builder) = 0;
mutable SpinLock<u8> m_refresh_lock;
mutable Mutex m_refresh_lock;
};
class ProcFSSystemBoolean : public ProcFSGlobalInformation {
@ -245,7 +245,7 @@ protected:
virtual bool output(KBufferBuilder& builder) = 0;
WeakPtr<ProcFSProcessDirectory> m_parent_directory;
mutable SpinLock<u8> m_refresh_lock;
mutable Mutex m_refresh_lock;
};
}