Konrad Rzeszutek Wilk
2013-Jun-07 19:29 UTC
[PATCH] 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>
---
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
Konrad Rzeszutek Wilk
2013-Jun-07 19:45 UTC
Re: [PATCH] xen/tmem: Don''t over-write tmem_frontswap_poolid after tmem_frontswap_init set it.
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 >
Bob Liu
2013-Jun-08 01:07 UTC
Re: [PATCH] xen/tmem: Don''t over-write tmem_frontswap_poolid after tmem_frontswap_init set it.
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