linux-kernel - [PATCH RFC v2 8/8] drm/i915: check if current->mm is not NULL

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Message-Id: <dda905a04a85cad003338732d712ff98c18c68cf.1667486144.git.mchehab@kernel.org>
Date:   Thu,  3 Nov 2022 14:51:38 +0000
From:   Mauro Carvalho Chehab <mchehab@...nel.org>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Christian König <christian.koenig@....com>,
        "Daniel Latypov" <dlatypov@...gle.com>,
        "Isabella Basso" <isabbasso@...eup.net>,
        Michał Winiarski <michal.winiarski@...el.com>,
        Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...il.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Matt Roper <matthew.d.roper@...el.com>,
        Matthew Auld <matthew.auld@...el.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        dri-devel@...ts.freedesktop.org, igt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, skhan@...uxfoundation.org
Subject: [PATCH RFC v2 8/8] drm/i915: check if current->mm is not NULL

The mmap tests require mm in order to work. Failing to do that
will cause a crash:

[  316.820722] BUG: kernel NULL pointer dereference, address: 00000000000000e8
[  316.822517] #PF: supervisor write access in kernel mode
[  316.823430] #PF: error_code(0x0002) - not-present page
[  316.824390] PGD 0 P4D 0
[  316.825357] Oops: 0002 [#1] PREEMPT SMP NOPTI
[  316.826350] CPU: 0 PID: 1517 Comm: kunit_try_catch Tainted: G     U           N 6.1.0-rc2-drm-266703e6f163+ #14
[  316.827503] Hardware name: Intel Corporation Tiger Lake Client Platform/TigerLake Y LPDDR4x T4 Crb, BIOS TGLSFWI1.R00.3243.A01.2006102133 06/10/2020
[  316.828633] RIP: 0010:down_write_killable+0x50/0x110
[  316.829756] Code: 24 10 45 31 c9 31 c9 41 b8 01 00 00 00 31 d2 31 f6 48 89 ef e8 e1 74 4a ff bf 01 00 00 00 e8 87 d6 46 ff 31 c0 ba 01 00 00 00 <f0> 48 0f b1 13 0f 94 c0 5a 84 c0 74 62 8b 05 49 12 e4 00 85 c0 74
[  316.830896] RSP: 0018:ffffc90001eabc58 EFLAGS: 00010246
[  316.832008] RAX: 0000000000000000 RBX: 00000000000000e8 RCX: 0000000000000000
[  316.833141] RDX: 0000000000000001 RSI: ffffffff81c94fc9 RDI: ffffffff81c94fc9
[  316.834195] RBP: 0000000000000158 R08: 0000000000000001 R09: 0000000000000000
[  316.835231] R10: 0000000000000000 R11: ffff8883a13350b8 R12: 0000000000000002
[  316.836259] R13: 0000000000000001 R14: 0000000000100000 R15: 00000000000000e8
[  316.837237] FS:  0000000000000000(0000) GS:ffff8883a3800000(0000) knlGS:0000000000000000
[  316.838214] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  316.839190] CR2: 00000000000000e8 CR3: 0000000002812003 CR4: 0000000000770ef0
[  316.840147] PKRU: 55555554
[  316.841099] Call Trace:
[  316.842047]  <TASK>
[  316.842990]  ? vm_mmap_pgoff+0x78/0x150
[  316.843936]  vm_mmap_pgoff+0x78/0x150
[  316.844884]  igt_mmap_offset+0x178/0x1b9 [i915]
[  316.846119]  __igt_mmap+0xfe/0x680 [i915]

Unfortunately, when KUnit module runs, it doesn't create an
user context, causing mmap tests to fail.

Signed-off-by: Mauro Carvalho Chehab <mchehab@...nel.org>
---

To avoid mailbombing on a large number of people, only mailing lists were C/C on the cover.
See [PATCH RFC v2 0/8] at: https://lore.kernel.org/all/cover.1667486144.git.mchehab@kernel.org/

 drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c
index add5ae56cd89..2c5f93e946b5 100644
--- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c
+++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c
@@ -1845,6 +1845,11 @@ int i915_gem_mman_live_selftests(struct drm_i915_private *i915)
 		SUBTEST(igt_mmap_gpu),
 	};
 
+	if (!current->mm) {
+		pr_err("Test called without an user context!\n");
+		return -EINVAL;
+	}
+
 	return i915_live_subtests(tests, i915);
 }
 EXPORT_SYMBOL_NS_GPL(i915_gem_mman_live_selftests, I915_SELFTEST);
-- 
2.38.1