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From:   Aleksandr Nogikh <aleksandrnogikh@gmail.com>
To:     davem@davemloft.net, kuba@kernel.org, johannes@sipsolutions.net
Cc:     edumazet@google.com, andreyknvl@google.com, dvyukov@google.com,
        elver@google.com, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, linux-wireless@vger.kernel.org,
        willemdebruijn.kernel@gmail.com,
        Aleksandr Nogikh <nogikh@google.com>
Subject: [PATCH v3 1/3] kernel: make kcov_common_handle consider the current context
Date:   Mon, 26 Oct 2020 15:08:49 +0000
Message-Id: <20201026150851.528148-2-aleksandrnogikh@gmail.com>
In-Reply-To: <20201026150851.528148-1-aleksandrnogikh@gmail.com>
References: <20201026150851.528148-1-aleksandrnogikh@gmail.com>
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From: Aleksandr Nogikh <nogikh@google.com>

kcov_common_handle is a method that is used to obtain a "default" KCOV
remote handle of the current process. The handle can later be passed
to kcov_remote_start in order to collect coverage for the processing
that is initiated by one process, but done in another. For details see
Documentation/dev-tools/kcov.rst and comments in kernel/kcov.c.

Presently, if kcov_common_handle is called in an IRQ context, it will
return a handle for the interrupted process. This may lead to
unreliable and incorrect coverage collection.

Adjust the behavior of kcov_common_handle in the following way. If it
is called in a task context, return the common handle for the
currently running task. Otherwise, return 0.

Signed-off-by: Aleksandr Nogikh <nogikh@google.com>
Reviewed-by: Andrey Konovalov <andreyknvl@google.com>
---
 kernel/kcov.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 6b8368be89c8..80bfe71bbe13 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -1023,6 +1023,8 @@ EXPORT_SYMBOL(kcov_remote_stop);
 /* See the comment before kcov_remote_start() for usage details. */
 u64 kcov_common_handle(void)
 {
+	if (!in_task())
+		return 0;
 	return current->kcov_handle;
 }
 EXPORT_SYMBOL(kcov_common_handle);
-- 
2.29.0.rc1.297.gfa9743e501-goog