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authorJosh Poimboeuf <jpoimboe@redhat.com>2017-03-06 20:20:29 +0300
committerJiri Kosina <jkosina@suse.cz>2017-03-08 11:38:43 +0300
commit3ec24776bfd09668079df7dca0c0136d80820ab4 (patch)
treeb9b1a65ff9a91a0f724d033f60645d2a78df47a3 /include/linux/livepatch.h
parent7c23b330011690705613a66a8239d2ca64a41d4d (diff)
downloadlinux-3ec24776bfd09668079df7dca0c0136d80820ab4.tar.xz
livepatch: allow removal of a disabled patch
Currently we do not allow patch module to unload since there is no method to determine if a task is still running in the patched code. The consistency model gives us the way because when the unpatching finishes we know that all tasks were marked as safe to call an original function. Thus every new call to the function calls the original code and at the same time no task can be somewhere in the patched code, because it had to leave that code to be marked as safe. We can safely let the patch module go after that. Completion is used for synchronization between module removal and sysfs infrastructure in a similar way to commit 942e443127e9 ("module: Fix mod->mkobj.kobj potentially freed too early"). Note that we still do not allow the removal for immediate model, that is no consistency model. The module refcount may increase in this case if somebody disables and enables the patch several times. This should not cause any harm. With this change a call to try_module_get() is moved to __klp_enable_patch from klp_register_patch to make module reference counting symmetric (module_put() is in a patch disable path) and to allow to take a new reference to a disabled module when being enabled. Finally, we need to be very careful about possible races between klp_unregister_patch(), kobject_put() functions and operations on the related sysfs files. kobject_put(&patch->kobj) must be called without klp_mutex. Otherwise, it might be blocked by enabled_store() that needs the mutex as well. In addition, enabled_store() must check if the patch was not unregisted in the meantime. There is no need to do the same for other kobject_put() callsites at the moment. Their sysfs operations neither take the lock nor they access any data that might be freed in the meantime. There was an attempt to use kobjects the right way and prevent these races by design. But it made the patch definition more complicated and opened another can of worms. See https://lkml.kernel.org/r/1464018848-4303-1-git-send-email-pmladek@suse.com [Thanks to Petr Mladek for improving the commit message.] Signed-off-by: Miroslav Benes <mbenes@suse.cz> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Reviewed-by: Petr Mladek <pmladek@suse.com> Acked-by: Miroslav Benes <mbenes@suse.cz> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Diffstat (limited to 'include/linux/livepatch.h')
-rw-r--r--include/linux/livepatch.h3
1 files changed, 3 insertions, 0 deletions
diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index ed90ad1605c1..194991ef9347 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -23,6 +23,7 @@
#include <linux/module.h>
#include <linux/ftrace.h>
+#include <linux/completion.h>
#if IS_ENABLED(CONFIG_LIVEPATCH)
@@ -114,6 +115,7 @@ struct klp_object {
* @list: list node for global list of registered patches
* @kobj: kobject for sysfs resources
* @enabled: the patch is enabled (but operation may be incomplete)
+ * @finish: for waiting till it is safe to remove the patch module
*/
struct klp_patch {
/* external */
@@ -125,6 +127,7 @@ struct klp_patch {
struct list_head list;
struct kobject kobj;
bool enabled;
+ struct completion finish;
};
#define klp_for_each_object(patch, obj) \