From mboxrd@z Thu Jan 1 00:00:00 1970 From: mst@redhat.com (Michael S. Tsirkin) Date: Sun, 19 May 2013 23:35:51 +0300 Subject: [PATCH v2 10/10] kernel: might_fault does not imply might_sleep In-Reply-To: <1368995002.6828.117.camel@gandalf.local.home> References: <1f85dc8e6a0149677563a2dfb4cef9a9c7eaa391.1368702323.git.mst@redhat.com> <20130516184041.GP19669@dyad.programming.kicks-ass.net> <20130519093526.GD19883@redhat.com> <1368966844.6828.111.camel@gandalf.local.home> <20130519133418.GA24381@redhat.com> <1368979579.6828.114.camel@gandalf.local.home> <20130519164009.GA2434@redhat.com> <1368995002.6828.117.camel@gandalf.local.home> Message-ID: <20130519203551.GA27708@redhat.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Sun, May 19, 2013 at 04:23:22PM -0400, Steven Rostedt wrote: > On Sun, 2013-05-19 at 19:40 +0300, Michael S. Tsirkin wrote: > > > OK I get it. So let me correct myself. The simple code > > that does something like this under a spinlock: > > > preempt_disable > > > pagefault_disable > > > error = copy_to_user > > > pagefault_enable > > > preempt_enable > > > > > is not doing anything wrong and should not get a warning, > > as long as error is handled correctly later. > > Right? > > I came in mid thread and I don't know the context. The context is that I want to change might_fault from might_sleep to might_sleep_if(!in_atomic()) so that above does not trigger warnings even with CONFIG_DEBUG_ATOMIC_SLEEP enabled. > Anyway, the above > looks to me as you just don't want to sleep. Exactly. upstream we can just do pagefault_disable but to make this code -rt ready it's best to do preempt_disable as well. > If you try to copy data to > user space that happens not to be currently mapped for any reason, you > will get an error. Even if the address space is completely valid. Is > that what you want? > > -- Steve > Yes, this is by design. We detect that and bounce the work to a thread outside any locks. Thanks, -- MST