[PATCH for-4.10] common/multicall: Increase debugability for bad hypercalls

[Andrew Cooper <andrew.cooper3@citrix.com>]

While investigating an issue (in a new codepath I'd introduced, as it turns
out), leaving interrupts disabled manifested as a subsequent op in the
multicall failing a check_lock() test.

The codepath would have hit the ASSERT_NOT_IN_ATOMIC on the return-to-guest
path, had it not hit the check_lock() first.

Call ASSERT_NOT_IN_ATOMIC() after each operation in the multicall, to make
failures more obvious.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: George Dunlap <George.Dunlap@eu.citrix.com>
CC: Jan Beulich <JBeulich@suse.com>
CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Tim Deegan <tim@xen.org>
CC: Wei Liu <wei.liu2@citrix.com>
CC: Julien Grall <julien.grall@arm.com>

As with the related check_lock() patch, this only affects debug builds, so is
a very low risk change for 4.10
---
 xen/common/multicall.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/xen/common/multicall.c b/xen/common/multicall.c
index c7af4e0..d98e59d 100644
--- a/xen/common/multicall.c
+++ b/xen/common/multicall.c
@@ -66,6 +66,13 @@ do_multicall(
 
         disp = arch_do_multicall_call(mcs);
 
+        /*
+         * In the unlikley event that a hypercall has left interrupts,
+         * spinlocks, or other things in a bad way, continuting the multicall
+         * will typically lead to far more subtle issues to debug.
+         */
+        ASSERT_NOT_IN_ATOMIC();
+
 #ifndef NDEBUG
         {
             /*
-- 
2.1.4


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