* [PATCH] xen/tmem: Don't over-write tmem_frontswap_poolid after tmem_frontswap_init set it.
@ 2013-06-07 19:29 Konrad Rzeszutek Wilk
2013-06-07 19:45 ` Konrad Rzeszutek Wilk
0 siblings, 1 reply; 3+ messages in thread
From: Konrad Rzeszutek Wilk @ 2013-06-07 19:29 UTC (permalink / raw)
To: linux-kernel, xen-devel; +Cc: dan.magenheimer, Konrad Rzeszutek Wilk
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>
---
drivers/xen/tmem.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
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 @@ 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);
--
1.8.1.4
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] xen/tmem: Don't over-write tmem_frontswap_poolid after tmem_frontswap_init set it.
2013-06-07 19:29 [PATCH] xen/tmem: Don't over-write tmem_frontswap_poolid after tmem_frontswap_init set it Konrad Rzeszutek Wilk
@ 2013-06-07 19:45 ` Konrad Rzeszutek Wilk
2013-06-08 1:07 ` Bob Liu
0 siblings, 1 reply; 3+ messages in thread
From: Konrad Rzeszutek Wilk @ 2013-06-07 19:45 UTC (permalink / raw)
To: linux-kernel, xen-devel, bob.liu; +Cc: dan.magenheimer
On Fri, Jun 07, 2013 at 12:29:15PM -0700, Konrad Rzeszutek Wilk wrote:
CC-ing Bob.
> 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>
> ---
> drivers/xen/tmem.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> 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 @@ 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);
> --
> 1.8.1.4
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] xen/tmem: Don't over-write tmem_frontswap_poolid after tmem_frontswap_init set it.
2013-06-07 19:45 ` Konrad Rzeszutek Wilk
@ 2013-06-08 1:07 ` Bob Liu
0 siblings, 0 replies; 3+ messages in thread
From: Bob Liu @ 2013-06-08 1:07 UTC (permalink / raw)
To: Konrad Rzeszutek Wilk; +Cc: linux-kernel, xen-devel, dan.magenheimer
On 06/08/2013 03:45 AM, Konrad Rzeszutek Wilk wrote:
> On Fri, Jun 07, 2013 at 12:29:15PM -0700, Konrad Rzeszutek Wilk wrote:
>
> CC-ing Bob.
>
>> 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>
Nice catch!
Reviewed-by: Bob Liu <bob.liu@oracle.com>
>> ---
>> drivers/xen/tmem.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> 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 @@ 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);
>> --
>> 1.8.1.4
>>
--
Regards,
-Bob
^ permalink raw reply [flat|nested] 3+ messages in thread
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2013-06-07 19:29 [PATCH] xen/tmem: Don't over-write tmem_frontswap_poolid after tmem_frontswap_init set it Konrad Rzeszutek Wilk
2013-06-07 19:45 ` Konrad Rzeszutek Wilk
2013-06-08 1:07 ` Bob Liu
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