adding some locking folks to the thread... On Fri, Feb 21, 2020 at 6:06 PM David Howells <dhowells@xxxxxxxxxx> wrote: > Jann Horn <jannh@xxxxxxxxxx> wrote: > > On Fri, Feb 21, 2020 at 1:24 PM David Howells <dhowells@xxxxxxxxxx> wrote: > > > What's the best way to write a lockdep assertion? > > > > > > BUG_ON(!lockdep_is_held(lock)); > > > > lockdep_assert_held(lock) is the normal way, I think - that will > > WARN() if lockdep is enabled and the lock is not held. > > Okay. But what's the best way with a seqlock_t? It has two dep maps in it. > Do I just ignore the one attached to the spinlock? Uuuh... very good question. Looking at how the seqlock_t helpers use the dep map of the seqlock, I don't think lockdep asserts work for asserting that you're in the read side of a seqlock? read_seqbegin_or_lock() -> read_seqbegin() -> read_seqcount_begin() -> seqcount_lockdep_reader_access() does seqcount_acquire_read() (which maps to lock_acquire_shared_recursive()), but immediately following that calls seqcount_release() (which maps to lock_release())? So I think lockdep won't consider you to be holding any locks after read_seqbegin_or_lock() if the lock wasn't taken?
