[PATCH v4 2/2] kexec: remove spinlock now that all KEXEC hypercall ops are protected at the top-level

[Eric DeVolder <eric.devolder@oracle.com>]

The spinlock in kexec_swap_images() was removed as
this function is only reachable on the kexec hypercall, which is
now protected at the top-level in do_kexec_op_internal(),
thus the local spinlock is no longer necessary.

Per recommendation from Jan Beulich and Andrew Cooper, I left
an ASSERT in place of the spin_lock().

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
Reviewed-by: Bhavesh Davda <bhavesh.davda@oracle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
v4: 04/19/2017
 - Fix ASSERT to work properly. Tested with Config.mk:debug=y

v3: 04/19/2017
 - Incorporated feedback from Jan Beulich and Andrew Cooper
   to leave an ASSERT where spin_lock() once was.

v2: 04/17/2017
 - Patch titled 'kexec: use hypercall_create_continuation to protect KEXEC ops'
 - Separated removal of spinlock in kexec_swap_images() into its own patch.

v1: 04/10/2017
 - Patch titled 'kexec: Add spinlock for the whole hypercall'
 - Removal of spinlock in kexec_swap_images() was part of other patch.
---
 xen/common/kexec.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/xen/common/kexec.c b/xen/common/kexec.c
index 253c204..96efa3b 100644
--- a/xen/common/kexec.c
+++ b/xen/common/kexec.c
@@ -820,7 +820,6 @@ static int kexec_exec(XEN_GUEST_HANDLE_PARAM(void) uarg)
 static int kexec_swap_images(int type, struct kexec_image *new,
                              struct kexec_image **old)
 {
-    static DEFINE_SPINLOCK(kexec_lock);
     int base, bit, pos;
     int new_slot, old_slot;
 
@@ -832,7 +831,7 @@ static int kexec_swap_images(int type, struct kexec_image *new,
     if ( kexec_load_get_bits(type, &base, &bit) )
         return -EINVAL;
 
-    spin_lock(&kexec_lock);
+    ASSERT(test_bit(KEXEC_FLAG_IN_HYPERCALL, &kexec_flags));
 
     pos = (test_bit(bit, &kexec_flags) != 0);
     old_slot = base + pos;
@@ -846,8 +845,6 @@ static int kexec_swap_images(int type, struct kexec_image *new,
     clear_bit(old_slot, &kexec_flags);
     *old = kexec_image[old_slot];
 
-    spin_unlock(&kexec_lock);
-
     return 0;
 }
 
-- 
2.7.4


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