On Mon, 2012-12-10 at 19:21 +0100, Oleg Nesterov wrote: > On 12/07, Oleg Nesterov wrote: > > > > On 12/06, Steven Rostedt wrote: > > > > > > You know reader locks can deadlock with each other, right? And this > > > isn't caught be lockdep yet. This is because rwlocks have been made to > > > be fair with writers. Before writers could be starved if a CPU always > > > let a reader in. Now if a writer is waiting, a reader will block behind > > > the writer. But this has introduced new issues with the kernel as > > > follows: > > > > > > > > > CPU0 CPU1 CPU2 CPU3 > > > ---- ---- ---- ---- > > > read_lock(A); > > > read_lock(B) > > > write_lock(A) <- block > > > write_lock(B) <- block > > > read_lock(B) <-block > > > > > > read_lock(A) <- block > > > > > > DEADLOCK! > > > > Really??? Oh I didn't know... > > > > Yes this was always true for rwsem, but rwlock_t? > > Sorry, please ignore my email. I misread your email. >
No prob, looking at what I wrote, I should have explicitly stated two different rwlocks. The only hint that I gave about two locks was (A) and (B). Even what I started with: "reader locks can deadlock with each other" is a bit ambiguous. So I can easily see the confusion. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
