On Wed, Oct 16, 2024 at 12:35:58PM +0800, lizhe.67@xxxxxxxxxxxxx wrote: > From: Li Zhe <lizhe.67@xxxxxxxxxxxxx> > > In the current kernel rwsem implementation, there is an interface to > downgrade write lock to read lock, but there is no interface to upgrade > a read lock to write lock. This means that in order to acquire write > lock while holding read lock, we have to release the read lock first and > then acquire the write lock, which will introduce some troubles in > concurrent programming. This patch set provides the 'upgrade_read' interface > to solve this problem. This interface can change a read lock to a write > lock. upgrade-read is fundamentally prone to deadlocks. Imagine two concurrent invocations, each waiting for all readers to go away before proceeding to upgrade to a writer. Any solution to fixing that will end up being semantically similar to dropping the read lock and acquiring a write lock -- there will not be a single continuous critical section. As such, this interface makes no sense.
