When running fault injection tests (CONFIG_FAULT_INJECTION_USERCOPY) against DAX/pmem read paths, the machine-check variant copy_to_user_iter_mc() is not covered because it skips the should_fail_usercopy() check that the normal copy_to_user_iter() has. This means the dax_copy_to_iter() code path used for pmem reads cannot be exercised by the usercopy fault injector, leaving a gap in test coverage for a path that has its own distinct error handling (it must not retry on #MC). Found by auditing all copy_to_user/copy_from_user helper variants in the file for consistent use of the fault injection hook and noticing copy_to_user_iter_mc() was the only one without it. Add the same should_fail_usercopy() check that copy_to_user_iter() has. Signed-off-by: Josh Law --- lib/iov_iter.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/lib/iov_iter.c b/lib/iov_iter.c index a5bb4fbd9d38..89e04066f737 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -204,6 +204,8 @@ static __always_inline size_t copy_to_user_iter_mc(void __user *iter_to, size_t progress, size_t len, void *from, void *priv2) { + if (should_fail_usercopy()) + return len; if (access_ok(iter_to, len)) { from += progress; instrument_copy_to_user(iter_to, from, len); -- 2.34.1