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authorMichael Ellerman <mpe@ellerman.id.au>2019-10-16 23:27:32 +1100
committerChristian Brauner <christian.brauner@ubuntu.com>2019-10-16 14:56:21 +0200
commitf418dddffc8007945fd5962380ebde770a240cf5 (patch)
treedc19f2a51d74c1bbcde5d1b1b2b7cbbaf47bf1ef /lib/test_user_copy.c
parentc90012ac85c24547e5c3468ef00aabf44aa7332d (diff)
downloadlwn-f418dddffc8007945fd5962380ebde770a240cf5.tar.gz
lwn-f418dddffc8007945fd5962380ebde770a240cf5.zip
usercopy: Avoid soft lockups in test_check_nonzero_user()
On a machine with a 64K PAGE_SIZE, the nested for loops in test_check_nonzero_user() can lead to soft lockups, eg: watchdog: BUG: soft lockup - CPU#4 stuck for 22s! [modprobe:611] Modules linked in: test_user_copy(+) vmx_crypto gf128mul crc32c_vpmsum virtio_balloon ip_tables x_tables autofs4 CPU: 4 PID: 611 Comm: modprobe Tainted: G L 5.4.0-rc1-gcc-8.2.0-00001-gf5a1a536fa14-dirty #1151 ... NIP __might_sleep+0x20/0xc0 LR __might_fault+0x40/0x60 Call Trace: check_zeroed_user+0x12c/0x200 test_user_copy_init+0x67c/0x1210 [test_user_copy] do_one_initcall+0x60/0x340 do_init_module+0x7c/0x2f0 load_module+0x2d94/0x30e0 __do_sys_finit_module+0xc8/0x150 system_call+0x5c/0x68 Even with a 4K PAGE_SIZE the test takes multiple seconds. Instead tweak it to only scan a 1024 byte region, but make it cross the page boundary. Fixes: f5a1a536fa14 ("lib: introduce copy_struct_from_user() helper") Suggested-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Reviewed-by: Aleksa Sarai <cyphar@cyphar.com> Acked-by: Christian Brauner <christian.brauner@ubuntu.com> Link: https://lore.kernel.org/r/20191016122732.13467-1-mpe@ellerman.id.au Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Diffstat (limited to 'lib/test_user_copy.c')
-rw-r--r--lib/test_user_copy.c22
1 files changed, 19 insertions, 3 deletions
diff --git a/lib/test_user_copy.c b/lib/test_user_copy.c
index ad2372727b1b..5ff04d8fe971 100644
--- a/lib/test_user_copy.c
+++ b/lib/test_user_copy.c
@@ -47,9 +47,25 @@ static bool is_zeroed(void *from, size_t size)
static int test_check_nonzero_user(char *kmem, char __user *umem, size_t size)
{
int ret = 0;
- size_t start, end, i;
- size_t zero_start = size / 4;
- size_t zero_end = size - zero_start;
+ size_t start, end, i, zero_start, zero_end;
+
+ if (test(size < 2 * PAGE_SIZE, "buffer too small"))
+ return -EINVAL;
+
+ /*
+ * We want to cross a page boundary to exercise the code more
+ * effectively. We also don't want to make the size we scan too large,
+ * otherwise the test can take a long time and cause soft lockups. So
+ * scan a 1024 byte region across the page boundary.
+ */
+ size = 1024;
+ start = PAGE_SIZE - (size / 2);
+
+ kmem += start;
+ umem += start;
+
+ zero_start = size / 4;
+ zero_end = size - zero_start;
/*
* We conduct a series of check_nonzero_user() tests on a block of