From: Petr Mladek <pmladek@suse.com>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Jiri Kosina <jikos@kernel.org>, Miroslav Benes <mbenes@suse.cz>,
Jason Baron <jbaron@akamai.com>,
Joe Lawrence <joe.lawrence@redhat.com>,
Evgenii Shatokhin <eshatokhin@virtuozzo.com>,
live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v13 06/12] livepatch: Simplify API by removing registration step
Date: Thu, 18 Oct 2018 14:33:29 +0200 [thread overview]
Message-ID: <20181018123329.5xvo5hjtqpbih4d2@pathway.suse.cz> (raw)
In-Reply-To: <20181017190657.dv3kwx467brzhdnz@treble>
On Wed 2018-10-17 14:06:57, Josh Poimboeuf wrote:
> On Mon, Oct 15, 2018 at 02:37:07PM +0200, Petr Mladek wrote:
> > @@ -319,96 +316,66 @@ forced it is guaranteed that no task sleeps or runs in the old code.
> > 5. Livepatch life-cycle
> > =======================
> >
> > -Livepatching defines four basic operations that define the life cycle of each
> > -live patch: registration, enabling, disabling and unregistration. There are
> > -several reasons why it is done this way.
> > +Livepatches get automatically enabled when the respective module is loaded.
>
> (only true if the module enables the patch in its init function)
Great catch! Will fix it.
> > @@ -502,6 +483,9 @@ static void klp_free_objects(struct klp_patch *patch)
> > }
> >
> > /*
> > + * The synchronous variant is needed when the patch is freed in
> > + * the klp_enable_patch() error paths.
> > + *
>
> Hm? This comment seems confusingly out of context.
Ah, the comment is just a left over from the previous version. It does
not longer make sense. I'll remove it.
> > @@ -528,6 +512,23 @@ static void klp_free_patch_finish(struct klp_patch *patch)
> > kobject_put(&patch->kobj);
> > wait_for_completion(&patch->finish);
> > }
> > +
> > + /* Put the module after the last access to struct klp_patch. */
> > + if (patch->module_put)
> > + module_put(patch->mod);
> > +}
> > +
> > +/*
> > + * The livepatch might be freed from sysfs interface created by the patch.
> > + * This work allows to wait until the interface is destroyed in a separate
> > + * context.
> > + */
> > +static void klp_free_patch_fn(struct work_struct *work)
>
> To clarify that it's a work function, how about calling it
> "klp_free_patch_work_fn"?
OK
> > static int klp_init_func(struct klp_object *obj, struct klp_func *func)
> > @@ -642,116 +643,38 @@ static int klp_init_patch(struct klp_patch *patch)
> > struct klp_object *obj;
> > int ret;
> >
> > - if (!patch->objs)
> > - return -EINVAL;
> > -
> > - mutex_lock(&klp_mutex);
> > -
> > patch->enabled = false;
> > - patch->forced = false;
> > + patch->module_put = false;
> > INIT_LIST_HEAD(&patch->list);
> > + INIT_WORK(&patch->free_work, klp_free_patch_fn);
> > init_completion(&patch->finish);
> >
> > + if (!patch->objs)
> > + return -EINVAL;
> > +
> > + /*
> > + * A reference is taken on the patch module to prevent it from being
> > + * unloaded.
> > + */
> > + if (!try_module_get(patch->mod))
> > + return -ENODEV;
>
> This comment isn't needed. It describes what try_module_get() does,
> which is common kernel knowledge.
Yup. I'll remove it. Note that it was there even before. I have just
moved it with the code.
> > + patch->module_put = true;
>
> The naming and semantics of the 'module_put' field are a little
> confusing. It's false in two cases:
>
> 1) try_module_get() failure
> 2) forced patch
>
> Maybe we can get rid of the need for the first case by moving the
> try_module_get() call to klp_enable_patch(), before calling
> klp_init_lists(). Then klp_free_patch_finish() will always be called
> with a module reference, so it doesn't have to check the 'module_put'
> field.
>
> We'd still need it for the force case, but then it can just be called
> 'forced' again.
Great idea! I'll do it in v14.
> > --- a/samples/livepatch/livepatch-callbacks-demo.c
> > +++ b/samples/livepatch/livepatch-callbacks-demo.c
> > @@ -184,22 +184,11 @@ static struct klp_patch patch = {
> >
> > static int livepatch_callbacks_demo_init(void)
> > {
> > - int ret;
> > -
> > - ret = klp_register_patch(&patch);
> > - if (ret)
> > - return ret;
> > - ret = klp_enable_patch(&patch);
> > - if (ret) {
> > - WARN_ON(klp_unregister_patch(&patch));
> > - return ret;
> > - }
> > - return 0;
> > + return klp_enable_patch(&patch);
> > }
> >
> > static void livepatch_callbacks_demo_exit(void)
> > {
> > - WARN_ON(klp_unregister_patch(&patch));
> > }
>
> This module exit function is no longer needed.
I have been there ;-) It is required. Otherewise the module
can't get removed. See the following code in kernel/module.c:
SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
unsigned int, flags)
{
[...]
/* If it has an init func, it must have an exit func to unload */
if (mod->init && !mod->exit) {
forced = try_force_unload(flags);
if (!forced) {
/* This module can't be removed */
ret = -EBUSY;
goto out;
}
}
Best Regards,
Petr
next prev parent reply other threads:[~2018-10-18 12:33 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-15 12:37 [PATCH v13 00/12] livepatch: Atomic replace feature Petr Mladek
2018-10-15 12:37 ` [PATCH v13 01/12] livepatch: Change void *new_func -> unsigned long new_addr in struct klp_func Petr Mladek
2018-10-15 12:37 ` [PATCH v13 02/12] livepatch: Helper macros to define livepatch structures Petr Mladek
2018-10-17 18:17 ` Josh Poimboeuf
2018-10-18 11:11 ` Petr Mladek
2018-10-18 12:58 ` Josh Poimboeuf
2018-10-24 11:28 ` Petr Mladek
2018-11-21 12:17 ` Miroslav Benes
2018-10-15 12:37 ` [PATCH v13 03/12] livepatch: Shuffle klp_enable_patch()/klp_disable_patch() code Petr Mladek
2018-10-15 12:37 ` [PATCH v13 04/12] livepatch: Consolidate klp_free functions Petr Mladek
2018-10-17 18:22 ` Josh Poimboeuf
2018-10-18 11:40 ` Petr Mladek
2018-11-21 13:59 ` Miroslav Benes
2018-11-21 14:40 ` Petr Mladek
2018-10-15 12:37 ` [PATCH v13 05/12] livepatch: Refuse to unload only livepatches available during a forced transition Petr Mladek
2018-10-17 18:35 ` Josh Poimboeuf
2018-10-18 12:09 ` Petr Mladek
2018-10-18 13:00 ` Josh Poimboeuf
2018-10-15 12:37 ` [PATCH v13 06/12] livepatch: Simplify API by removing registration step Petr Mladek
2018-10-17 19:06 ` Josh Poimboeuf
2018-10-18 12:33 ` Petr Mladek [this message]
2018-10-15 12:37 ` [PATCH v13 07/12] livepatch: Use lists to manage patches, objects and functions Petr Mladek
2018-10-17 20:31 ` Josh Poimboeuf
2018-10-18 12:34 ` Petr Mladek
2018-10-15 12:37 ` [PATCH v13 08/12] livepatch: Add atomic replace Petr Mladek
2018-11-23 12:00 ` Miroslav Benes
2018-10-15 12:37 ` [PATCH v13 09/12] livepatch: Remove Nop structures when unused Petr Mladek
2018-10-17 20:48 ` Josh Poimboeuf
2018-10-18 12:40 ` Petr Mladek
2018-10-15 12:37 ` [PATCH v13 10/12] livepatch: Atomic replace and cumulative patches documentation Petr Mladek
2018-10-15 12:37 ` [PATCH v13 11/12] livepatch: Remove ordering and refuse loading conflicting patches Petr Mladek
2018-10-15 12:37 ` [PATCH v13 12/12] selftests/livepatch: introduce tests Petr Mladek
2018-10-15 19:46 ` Joe Lawrence
2018-10-17 20:48 ` Josh Poimboeuf
2018-10-18 13:34 ` [PATCH v13 00/12] livepatch: Atomic replace feature Josh Poimboeuf
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