From: Petr Mladek <pmladek@suse.com>
To: Rik van Riel <riel@surriel.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>,
linux-kernel@vger.kernel.org, live-patching@vger.kernel.org,
kernel-team@fb.com, Jiri Kosina <jikos@kernel.org>,
Miroslav Benes <mbenes@suse.cz>,
Joe Lawrence <joe.lawrence@redhat.com>,
Breno Leitao <leitao@debian.org>
Subject: Re: [PATCH v4] livepatch: fix race between fork and KLP transition
Date: Thu, 28 Jul 2022 17:37:26 +0200 [thread overview]
Message-ID: <YuKtNtOshtRfeMn7@alley> (raw)
In-Reply-To: <20220727102437.34530586@imladris.surriel.com>
On Wed 2022-07-27 10:24:37, Rik van Riel wrote:
> v4: address changelog comments by Josh (thank you)
>
> ---8<---
> When a KLP fails to apply, klp_reverse_transition will clear the
> TIF_PATCH_PENDING flag on all tasks, except for newly created tasks
> which are not on the task list yet.
It actually is not true. klp_reverse_transtion() clears TIF_PATCH_FLAG only
temporary when it waits until all processes leave the ftrace
handler. It sets TIF_PATCH_FLAG once again for all tasks by calling
klp_start_transition().
The difference is important. The WARN_ON_ONCE() in
klp_complete_transition() will be printed when fork() copied
TIF_PATCH_FLAG before it was set again.
Anyway, the important thing is that TIF_PATCH_FLAG and task->patch_state
might be incompatible because fork() copies them at different times.
klp_copy_process() must make sure that they are in sync. And
it must be done under tasklist_lock when the child is added
to the global task list.
Best Regards,
Petr
next prev parent reply other threads:[~2022-07-28 15:37 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-20 16:10 [PATCH,RFC] livepatch: fix race between fork and klp_reverse_transition Rik van Riel
2022-07-21 23:23 ` Song Liu
2022-07-22 15:30 ` Petr Mladek
2022-07-22 19:01 ` [PATCH v2] " Rik van Riel
2022-07-25 13:32 ` Petr Mladek
2022-07-25 13:49 ` [PATCH v3] " Rik van Riel
2022-07-27 0:10 ` Josh Poimboeuf
2022-07-27 0:26 ` Rik van Riel
2022-07-28 15:20 ` Petr Mladek
2022-07-27 14:24 ` [PATCH v4] livepatch: fix race between fork and KLP transition Rik van Riel
2022-07-28 15:37 ` Petr Mladek [this message]
2022-08-02 20:07 ` Rik van Riel
2022-08-04 13:06 ` Petr Mladek
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