On Mon, 2009-12-14 at 13:42 +0100, Kay Sievers wrote: > On Mon, Dec 14, 2009 at 12:30, Jon Masters <jonathan@xxxxxxxxxxxxxx> wrote: > > On Mon, 2009-12-14 at 11:24 +0100, Kay Sievers wrote: > >> On Mon, Dec 14, 2009 at 02:12, Jon Masters <jonathan@xxxxxxxxxxxxxx> wrote: > >> > On Sat, 2009-12-12 at 04:29 -0500, Jon Masters wrote: > >> > > >> >> FYI I am diagnosing an unlikely locking issue on a RHEL system right now > >> >> that triggers when you have a read-only filesystem and can't use file > >> >> locks. I know we ripped out a lot of that code since in upstream but I > >> >> might need to address this differently. I'll followup with my findings. > >> > > >> > I have written a sysV shared memory locking mechanism that using an shm > >> > segment in the case that the filesystem is mounted read-only. I'll > >> > finish the work on the RHEL bug and then forward port it, and post. We > >> > can probably re-introduce this because it works in a read-only context > >> > and can't be abused by a user to prevent module loading because the IPC > >> > shm segment is user-specific. Only downside is (optional, I guess) > >> > dependency on sysV shm. But I don't think we honestly have anyone > >> > wanting to use m-i-t on a system without such things compiled in. > >> > >> Why would we need anything like that? Shouldn't the load syscall > >> serialize all that properly? > > > > It doesn't quite though (in the 2.6.18 kernel I'm focusing on right now, > > upstream has some slight changes in the module loader code since then). > > We only run under stop machine during the actual link and unlink, > > I don't think we ever run under stop_machine Let me be clear, "we" do in the sense that the kernel module.c code requires a stop_machine in order to perform the actual link/unlink operation of the module. And certainly more so in older kernels. But anyway, we don't use it very much in any case, so we're mostly able to run other modprobe instances that might come along. Jon. -- To unsubscribe from this list: send the line "unsubscribe linux-modules" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
