xen/tmem: Don't over-write tmem_frontswap_poolid after tmem_frontswap_init set it.
Commit 10a7a0771399a57a297fca9615450dbb3f88081a ("xen: tmem: enable Xen
tmem shim to be built/loaded as a module") allows the tmem module
to be loaded any time. For this work the frontswap API had to
be able to asynchronously to call tmem_frontswap_init before
or after the swap image had been set. That was added in git
commit 905cd0e1bf9ffe82d6906a01fd974ea0f70be97a
("mm: frontswap: lazy initialization to allow tmem backends to build/run as modules").
Which means we could do this (The common case):
modprobe tmem [so calls frontswap_register_ops, no ->init]
modifies tmem_frontswap_poolid = -1
swapon /dev/xvda1 [__frontswap_init, calls -> init, tmem_frontswap_poolid is
< 0 so tmem hypercall done]
Or the failing one:
swapon /dev/xvda1 [calls __frontswap_init, sets the need_init bitmap]
modprobe tmem [calls frontswap_register_ops, -->init calls, finds out
tmem_frontswap_poolid is 0, does not make a hypercall.
Later in the module_init, sets tmem_frontswap_poolid=-1]
Which meant that in the failing case we would not call the hypercall
to initialize the pool and never be able to make any frontswap
backend calls.
Moving the frontswap_register_ops after setting the tmem_frontswap_poolid
fixes it.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Bob Liu <bob.liu@oracle.com>
diff --git a/drivers/xen/tmem.c b/drivers/xen/tmem.c
index cc072c6..0f0493c 100644
--- a/drivers/xen/tmem.c
+++ b/drivers/xen/tmem.c
@@ -379,10 +379,10 @@
#ifdef CONFIG_FRONTSWAP
if (tmem_enabled && frontswap) {
char *s = "";
- struct frontswap_ops *old_ops =
- frontswap_register_ops(&tmem_frontswap_ops);
+ struct frontswap_ops *old_ops;
tmem_frontswap_poolid = -1;
+ old_ops = frontswap_register_ops(&tmem_frontswap_ops);
if (IS_ERR(old_ops) || old_ops) {
if (IS_ERR(old_ops))
return PTR_ERR(old_ops);
