put_device(&adap->dev) might free the memory pointed to by `adap`,
so we shouldn't read adap->owner after that.
Fix by saving module pointer before calling put_device().
Signed-off-by: Michał Mirosław <[email protected]>
---
drivers/i2c/i2c-core-base.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index 2c59dd748a49..5d694f8ce9ef 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -2464,11 +2464,14 @@ EXPORT_SYMBOL(i2c_get_adapter);
void i2c_put_adapter(struct i2c_adapter *adap)
{
+ struct module *owner;
+
if (!adap)
return;
+ owner = adap->owner;
put_device(&adap->dev);
- module_put(adap->owner);
+ module_put(owner);
}
EXPORT_SYMBOL(i2c_put_adapter);
--
2.30.2
Hi Michał,
I finally had a look at your patch...
> put_device(&adap->dev) might free the memory pointed to by `adap`,
> so we shouldn't read adap->owner after that.
>
> Fix by saving module pointer before calling put_device().
... and found a different approach for this problem from 2019:
http://patchwork.ozlabs.org/project/linux-i2c/patch/[email protected]/
I think this is also proper. I found other subsystems in the kernel
first putting the module, then the device. Do you see problems with the
above patch?
Thanks for looking into the issue!
Wolfram
>
> Signed-off-by: Michał Mirosław <[email protected]>
> ---
> drivers/i2c/i2c-core-base.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index 2c59dd748a49..5d694f8ce9ef 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -2464,11 +2464,14 @@ EXPORT_SYMBOL(i2c_get_adapter);
>
> void i2c_put_adapter(struct i2c_adapter *adap)
> {
> + struct module *owner;
> +
> if (!adap)
> return;
>
> + owner = adap->owner;
> put_device(&adap->dev);
> - module_put(adap->owner);
> + module_put(owner);
> }
> EXPORT_SYMBOL(i2c_put_adapter);
>
> --
> 2.30.2
>
On Tue, Jun 14, 2022 at 09:45:42PM +0200, Wolfram Sang wrote:
> Hi Micha?,
>
> I finally had a look at your patch...
>
> > put_device(&adap->dev) might free the memory pointed to by `adap`,
> > so we shouldn't read adap->owner after that.
> >
> > Fix by saving module pointer before calling put_device().
>
> ... and found a different approach for this problem from 2019:
>
> http://patchwork.ozlabs.org/project/linux-i2c/patch/[email protected]/
>
> I think this is also proper. I found other subsystems in the kernel
> first putting the module, then the device. Do you see problems with the
> above patch?
>
> Thanks for looking into the issue!
Hi!
I looked briefly at the kobject machinery and it seems to ignore module
dependencies. So while both approaches might work, I'd usually reverse
the order the init code is using: in this case module_get+device_get,
so on release: device_put+module_put. I don't know what keeps the kernel
from unloading the module after module_put() and before the function
returns, but I assume that would blow up for both patches.
Best Regards
Micha??Miros?aw
> >
> > Signed-off-by: Micha? Miros?aw <[email protected]>
> > ---
> > drivers/i2c/i2c-core-base.c | 5 ++++-
> > 1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> > index 2c59dd748a49..5d694f8ce9ef 100644
> > --- a/drivers/i2c/i2c-core-base.c
> > +++ b/drivers/i2c/i2c-core-base.c
> > @@ -2464,11 +2464,14 @@ EXPORT_SYMBOL(i2c_get_adapter);
> >
> > void i2c_put_adapter(struct i2c_adapter *adap)
> > {
> > + struct module *owner;
> > +
> > if (!adap)
> > return;
> >
> > + owner = adap->owner;
> > put_device(&adap->dev);
> > - module_put(adap->owner);
> > + module_put(owner);
> > }
> > EXPORT_SYMBOL(i2c_put_adapter);
> >
> > --
> > 2.30.2
> >
--
Micha? Miros?aw
Hi Michał,
> I looked briefly at the kobject machinery and it seems to ignore module
> dependencies. So while both approaches might work, I'd usually reverse
Thanks for checking!
> the order the init code is using: in this case module_get+device_get,
> so on release: device_put+module_put. I don't know what keeps the kernel
I agree this is good style. I'll add a comment why we reverse the order.
This will be also good to avoid regressions.
> from unloading the module after module_put() and before the function
> returns, but I assume that would blow up for both patches.
Yes. There are other users in the kernel doing it like this (RTC and
regmap IIRC), so I think problems would have become visible by then.
Thank you for your help!
Wolfram