Messages in this thread | | | Date | Fri, 5 Apr 2019 10:00:02 -0600 | From | Tycho Andersen <> | Subject | Re: [PATCH] x86/entry: re-enable interrupts before exiting |
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On Fri, Apr 05, 2019 at 10:58:33AM -0500, Josh Poimboeuf wrote: > On Fri, Apr 05, 2019 at 09:35:24AM -0600, Tycho Andersen wrote: > > If the kernel oopses in an interrupt, nothing re-enables interrupts: > > > > Aug 23 19:30:27 xpfo kernel: [ 38.302714] BUG: sleeping function called from invalid context at > > ./include/linux/percpu-rwsem.h:33 > > Aug 23 19:30:27 xpfo kernel: [ 38.303837] in_atomic(): 0, irqs_disabled(): 1, pid: 1970, name: > > lkdtm_xpfo_test > > Aug 23 19:30:27 xpfo kernel: [ 38.304758] CPU: 3 PID: 1970 Comm: lkdtm_xpfo_test Tainted: G D > > 4.13.0-rc5+ #228 > > Aug 23 19:30:27 xpfo kernel: [ 38.305813] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS > > 1.10.1-1ubuntu1 04/01/2014 > > Aug 23 19:30:27 xpfo kernel: [ 38.306926] Call Trace: > > Aug 23 19:30:27 xpfo kernel: [ 38.307243] dump_stack+0x63/0x8b > > Aug 23 19:30:27 xpfo kernel: [ 38.307665] ___might_sleep+0xec/0x110 > > Aug 23 19:30:27 xpfo kernel: [ 38.308139] __might_sleep+0x45/0x80 > > Aug 23 19:30:27 xpfo kernel: [ 38.308593] exit_signals+0x21/0x1c0 > > Aug 23 19:30:27 xpfo kernel: [ 38.309046] ? blocking_notifier_call_chain+0x11/0x20 > > Aug 23 19:30:27 xpfo kernel: [ 38.309677] do_exit+0x98/0xbf0 > > Aug 23 19:30:27 xpfo kernel: [ 38.310078] ? smp_reader+0x27/0x40 [lkdtm] > > Aug 23 19:30:27 xpfo kernel: [ 38.310604] ? kthread+0x10f/0x150 > > Aug 23 19:30:27 xpfo kernel: [ 38.311045] ? read_user_with_flags+0x60/0x60 [lkdtm] > > Aug 23 19:30:27 xpfo kernel: [ 38.311680] rewind_stack_do_exit+0x17/0x20 > > > > do_exit() expects to be called in a well-defined environment, so let's > > re-enable interrupts after unwinding the stack, in case they were disabled. > > > > Note that if any spinlocks are held, etc. we'll also get the above warning, > > so this isn't a silver bullet. So, let's add a C helper in case someone > > wants to add fancier lock busting or if we've forgotten to unwind something > > else. > > > > I've had to add back in the hack that Josh removed in 8c1f75587a18 > > ("x86/entry/64: Add unwind hint annotations") with the loop after the call, > > because for whatever reason without that I get a warning: > > > > AS arch/x86/entry/entry_64.o > > arch/x86/entry/entry_64.o: warning: objtool: .entry.text: unexpected end of section > > > > It seems to actually work fine for me though, since the new helper is also > > __noreturn. Perhaps there's a better way to do this? > > Unfortunately, objtool doesn't have a way to detect noreturn functions > in other objects, so they're hard-coded in a list. You can add > __finish_rewind_stack_do_exit to the global_noreturns array in > tools/objtool/check.c.
Awesome, this is the magic I was missing. Thanks!
Tycho
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