linux-kernel - [PATCH v2 1/3] kernel: make kcov_common

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Date:   Fri,  9 Oct 2020 17:02:00 +0000
From:   Aleksandr Nogikh <a.nogikh@...il.com>
To:     davem@...emloft.net, kuba@...nel.org, johannes@...solutions.net,
        akpm@...ux-foundation.org
Cc:     edumazet@...gle.com, andreyknvl@...gle.com, dvyukov@...gle.com,
        elver@...gle.com, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
        nogikh@...gle.com
Subject: [PATCH v2 1/3] kernel: make kcov_common_handle consider the current context

From: Aleksandr Nogikh <nogikh@...gle.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 a hard 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. It will make the returned
value more reliable and also will make it possible to use
kcov_remote_handle in routines that can be called from any context.

Signed-off-by: Aleksandr Nogikh <nogikh@...gle.com>
---
v2:
* Added this patch to the series.
---
 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);
-- 
2.28.0.1011.ga647a8990f-goog