On Tue, 09 Feb, at 05:52:34PM, Ard Biesheuvel wrote: > On 8 February 2016 at 20:37, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > > On Feb 4, 2016 5:58 AM, "Ard Biesheuvel" <ard.biesheuvel@xxxxxxxxxx> wrote: > >> > >> OK, since Sai has confirmed that Windows leaves interrupts enabled when > >> calling the EFI variable store related runtime services, we should be able > >> to do the same for Linux, or at least be slightly more confident that we > >> won't have to back out this change later. > > > > Could this use a mutex instead of a spinlock? > > > > When I first started working on this code, I proposed using a mutex, > but at the time, we still had the efi-pstore case to worry about > http://article.gmane.org/gmane.linux.kernel.efi/4112 > > In the mean time, we have modified the efi-pstore code so it simply > gives up when the EFI varstore is busy, and we also got rid of the NMI > special case where locks are ignored. In summary, it sounds to me that > moving to a mutex should be feasible, but I am only really familiar > with the ARM side of the implementation, which is far less complex > than the x86 side, so Matt should confirm. You cannot touch mutexes from interrupt context, not even to perform a mutex_trylock(), and that's the problem. Since the efi-pstore code can run from interrupt context we need to use a locking primitive that works, even though we have all that non-blocking logic. -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
