read_coredump_req() gets the leftover wrong twice. It takes the absolute difference of the two sizes, so a test binary that knows a larger struct coredump_req than the kernel sends tries to discard bytes that were never sent. And it hands recv() sizeof(buffer) instead of the number of bytes it wants. So MSG_WAITALL waits for a whole page. Either one blocks until the kernel closes the socket. Which it won't because it is waiting for the coredump ack... Its benign today because struct coredump_req hasn't grown. But let's fix it for the future. Compute the leftover as what the kernel sent beyond what was consumed. Fixes: 59cd658eaf40 ("selftests/coredump: add coredump server selftests") Signed-off-by: Christian Brauner (Amutable) --- tools/testing/selftests/coredump/coredump_test_helpers.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/tools/testing/selftests/coredump/coredump_test_helpers.c b/tools/testing/selftests/coredump/coredump_test_helpers.c index 2a20faf9cb0a..524fa5370593 100644 --- a/tools/testing/selftests/coredump/coredump_test_helpers.c +++ b/tools/testing/selftests/coredump/coredump_test_helpers.c @@ -235,10 +235,10 @@ bool read_coredump_req(int fd, struct coredump_req *req) fprintf(stderr, "Read coredump request with size %u and mask 0x%llx\n", req->size, (unsigned long long)req->mask); - if (user_size > kernel_size) - remaining_size = user_size - kernel_size; - else + if (kernel_size > user_size) remaining_size = kernel_size - user_size; + else + remaining_size = 0; if (PAGE_SIZE <= remaining_size) return false; @@ -250,7 +250,7 @@ bool read_coredump_req(int fd, struct coredump_req *req) if (remaining_size) { char buffer[PAGE_SIZE]; - ret = recv(fd, buffer, sizeof(buffer), MSG_WAITALL); + ret = recv(fd, buffer, remaining_size, MSG_WAITALL); if (ret != remaining_size) return false; fprintf(stderr, "Discarded %zu bytes of data after coredump request\n", remaining_size); -- 2.53.0