On 10/16, Linus Torvalds wrote: > > On Mon, Oct 15, 2012 at 12:10 PM, Oleg Nesterov <o...@redhat.com> wrote: > > This patch adds the new sleeping lock, brw_mutex. Unlike rw_semaphore > > it allows multiple writers too, just "read" and "write" are mutually > > exclusive. > > So those semantics just don't sound sane. It's also not what any kind > of normal "rw" lock ever does.
Yes, this is not usual. And initially I made brw_sem which allows only 1 writer, but then I changed this patch. > So can you explain why these particular insane semantics are useful, > and what for? To allow multiple uprobe_register/unregister at the same time. Mostly to not add the "regression", currently this is possible. It is not that I think this is terribly important, but still. And personally I think that "multiple writers" is not necessarily insane in general. Suppose you have the complex object/subsystem, the readers can use a single brw_mutex to access it "lockless", start_read() is very cheap. But start_write() is slow. Multiple writes can use the fine-grained inside the start_write/end_write section and do not block each other. Oleg. -- 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/
