[S390] kvm: fix sleeping function ... at mm/page_alloc.c:2260

commit cc772456
    [S390] fix list corruption in gmap reverse mapping

added a potential dead lock:

BUG: sleeping function called from invalid context at mm/page_alloc.c:2260
in_atomic(): 1, irqs_disabled(): 0, pid: 1108, name: qemu-system-s39
3 locks held by qemu-system-s39/1108:
 #0:  (&kvm->slots_lock){+.+.+.}, at: [<000003e004866542>] kvm_set_memory_region+0x3a/0x6c [kvm]
 #1:  (&mm->mmap_sem){++++++}, at: [<0000000000123790>] gmap_map_segment+0x9c/0x298
 #2:  (&(&mm->page_table_lock)->rlock){+.+.+.}, at: [<00000000001237a8>] gmap_map_segment+0xb4/0x298
CPU: 0 Not tainted 3.1.3 #45
Process qemu-system-s39 (pid: 1108, task: 00000004f8b3cb30, ksp: 00000004fd5978d0)
00000004fd5979a0 00000004fd597920 0000000000000002 0000000000000000
       00000004fd5979c0 00000004fd597938 00000004fd597938 0000000000617e96
       0000000000000000 00000004f8b3cf58 0000000000000000 0000000000000000
       000000000000000d 000000000000000c 00000004fd597988 0000000000000000
       0000000000000000 0000000000100a18 00000004fd597920 00000004fd597960
Call Trace:
([<0000000000100926>] show_trace+0xee/0x144)
 [<0000000000131f3a>] __might_sleep+0x12a/0x158
 [<0000000000217fb4>] __alloc_pages_nodemask+0x224/0xadc
 [<0000000000123086>] gmap_alloc_table+0x46/0x114
 [<000000000012395c>] gmap_map_segment+0x268/0x298
 [<000003e00486b014>] kvm_arch_commit_memory_region+0x44/0x6c [kvm]
 [<000003e004866414>] __kvm_set_memory_region+0x3b0/0x4a4 [kvm]
 [<000003e004866554>] kvm_set_memory_region+0x4c/0x6c [kvm]
 [<000003e004867c7a>] kvm_vm_ioctl+0x14a/0x314 [kvm]
 [<0000000000292100>] do_vfs_ioctl+0x94/0x588
 [<0000000000292688>] SyS_ioctl+0x94/0xac
 [<000000000061e124>] sysc_noemu+0x22/0x28
 [<000003fffcd5e7ca>] 0x3fffcd5e7ca
3 locks held by qemu-system-s39/1108:
 #0:  (&kvm->slots_lock){+.+.+.}, at: [<000003e004866542>] kvm_set_memory_region+0x3a/0x6c [kvm]
 #1:  (&mm->mmap_sem){++++++}, at: [<0000000000123790>] gmap_map_segment+0x9c/0x298
 #2:  (&(&mm->page_table_lock)->rlock){+.+.+.}, at: [<00000000001237a8>] gmap_map_segment+0xb4/0x298

Fix this by freeing the lock on the alloc path. This is ok, since the
gmap table is never freed until we call gmap_free, so the table we are
walking cannot go.
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/mm/pgtable.c

@@ -267,7 +267,10 @@ static int gmap_alloc_table(struct gmap *gmap,
 	struct page *page;
 	unsigned long *new;
 
+	/* since we dont free the gmap table until gmap_free we can unlock */
+	spin_unlock(&gmap->mm->page_table_lock);
 	page = alloc_pages(GFP_KERNEL, ALLOC_ORDER);
+	spin_lock(&gmap->mm->page_table_lock);
 	if (!page)
 		return -ENOMEM;
 	new = (unsigned long *) page_to_phys(page);