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xen/tmem: Don't over-write tmem_frontswap_poolid after tmem_frontswap_init set it.

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Commit 10a7a07713 ("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 905cd0e1bf
("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>
This commit is contained in:
Konrad Rzeszutek Wilk 2013-06-07 15:26:03 -04:00
parent 466318a87f
commit b2c75c446a
1 changed files with 2 additions and 2 deletions
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4
drivers/xen/tmem.c
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@ -379,10 +379,10 @@ static int xen_tmem_init(void)
#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);