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Date: Wed, 31 Mar 2010 21:23:02 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: Jiaying Zhang <jiayingz@...gle.com> Cc: Steven Rostedt <srostedt@...hat.com>, Ingo Molnar <mingo@...e.hu>, Michael Rubin <mrubin@...gle.com>, David Sharp <dhsharp@...gle.com>, linux-kernel@...r.kernel.org Subject: Re: lockup in rb_get_reader_page On Wed, 2010-03-31 at 18:14 -0700, Jiaying Zhang wrote: > On Wed, Mar 31, 2010 at 5:28 PM, Steven Rostedt <rostedt@...dmis.org> wrote: > > > > Are you doing reads from interrupt context? > > > No. We are using a user-space reader that reads ring buffer via syscall > or ioctl. But even though we don't read from interrupt context, as I > understand, we can still have a reader on another cpuB reads cpuA's > buffer when the writer on cpuA moves the head page. Will we have > any problem in that case? Nope, unless that write hangs for some reason ;-) The read may spin waiting for a writer to finish, hence it just can not preempt a writer in an interrupt context, because then it may spin forever, because it is blocking the writer. But if a writer is on another CPU, then all is well. In fact, the ring buffer was designed with that in mind. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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