Re: [LTP] [PATCH v9] mremap07.c: New test for mremap() with MREMAP_DONTUNMAP

[Li Wang <wangli.ahau@gmail.com>]

Hi Wei,

Wei Gao wrote:

> This test verifies the mremap() syscall with the MREMAP_DONTUNMAP flag.
> It uses userfaultfd to verify that accessing the old memory region
> correctly triggers a page fault after the mapping has been moved.
> 
> MREMAP_DONTUNMAP behavior with userfaultfd was not covered by existing
> mremap tests. This test provides coverage for the feature requested in
> the linked issue.
> 
> Closes: https://github.com/linux-test-project/ltp/issues/1168
> Signed-off-by: Wei Gao <wegao@suse.com>
> ---
> v8->v9:
> - Removed `MREMAP_DONTUNMAP` check from `configure.ac` and moved fallback to `include/lapi/mmap.h`.
> - Renamed address variables to `old_addr` and `new_addr` for clarity.
> - Replaced hardcoded strings with `TEST_STRING_A` and `TEST_STRING_B` macros.
> - Improved code formatting and indentation.
> - Removed `.min_kver = "5.7"` in favor of dynamic feature detection.
> - Added runtime `EINVAL` check to trigger `TCONF` on unsupported kernels.
> - Added verification logic for data content at `new_addr`.
> - Fixed stability issues for multiple test iterations (`-i` option).

Patch merged with some improvements (for better readability and reliability):

--- a/testcases/kernel/syscalls/mremap/mremap07.c
+++ b/testcases/kernel/syscalls/mremap/mremap07.c
@@ -19,7 +19,6 @@
 #include "tst_safe_pthread.h"
 #include "lapi/userfaultfd.h"
 #include "lapi/mmap.h"
-#include "config.h"

 static int page_size;
 static int uffd = -1;
@@ -33,33 +32,24 @@ static void *fault_handler_thread(void *arg LTP_ATTRIBUTE_UNUSED)
 {
        struct uffd_msg msg;
        struct uffdio_copy uffdio_copy;
+       struct pollfd pollfd = { .fd = uffd, .events = POLLIN };

        TST_CHECKPOINT_WAIT(0);

-       struct pollfd pollfd;
-
-       pollfd.fd = uffd;
-       pollfd.events = POLLIN;
-
-       int nready = poll(&pollfd, 1, -1);
-
-       if (nready == -1)
+       if (poll(&pollfd, 1, -1) == -1)
                tst_brk(TBROK | TERRNO, "poll() failed");

-       if (nready == 0)
-               tst_brk(TBROK, "poll() timed out unexpectedly");
-
        SAFE_READ(1, uffd, &msg, sizeof(msg));

        if (msg.event != UFFD_EVENT_PAGEFAULT)
                tst_brk(TBROK, "Received unexpected UFFD_EVENT: %d", msg.event);

-       if ((char *)msg.arg.pagefault.address != old_addr)
+       if (msg.arg.pagefault.address != (unsigned long)old_addr)
                tst_brk(TBROK, "Page fault on unexpected address: %p",
-                       (void *)msg.arg.pagefault.address);
+                               (void *)msg.arg.pagefault.address);

        tst_res(TINFO, "Userfaultfd handler caught a page fault at %p",
-               (void *)msg.arg.pagefault.address);
+                       (void *)msg.arg.pagefault.address);

        uffdio_copy.src = (unsigned long)new_addr;
        uffdio_copy.dst = (unsigned long)old_addr;
@@ -73,12 +63,32 @@ static void *fault_handler_thread(void *arg LTP_ATTRIBUTE_UNUSED)
        return NULL;
 }

+static void check_mremap_dontunmap(void)
+{
+       char *test = SAFE_MMAP(NULL, page_size, PROT_READ | PROT_WRITE,
+                               MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+
+       char *tmp = mremap(test, page_size, page_size,
+                               MREMAP_DONTUNMAP | MREMAP_MAYMOVE, NULL);
+
+       if (tmp == MAP_FAILED) {
+               if (errno == EINVAL)
+                       tst_brk(TCONF | TERRNO,
+                                       "MREMAP_DONTUNMAP not supported");
+               tst_brk(TBROK | TERRNO, "mremap failed");
+       }
+
+       SAFE_MUNMAP(tmp, page_size);
+       SAFE_MUNMAP(test, page_size);
+}
+
 static void setup(void)
 {
        struct uffdio_api uffdio_api;
        struct uffdio_register uffdio_register;

        page_size = getpagesize();
+       check_mremap_dontunmap();
        uffd = SAFE_USERFAULTFD(O_CLOEXEC | O_NONBLOCK, true);

        uffdio_api.api = UFFD_API;
@@ -92,7 +102,7 @@ static void setup(void)

        tst_res(TINFO, "Original mapping created at %p", (void *)old_addr);

-       strcpy(old_addr, TEST_STRING_A);
+       memcpy(old_addr, TEST_STRING_A, sizeof(TEST_STRING_A));

        uffdio_register.range.start = (unsigned long)old_addr;
        uffdio_register.range.len = page_size;
@@ -118,23 +128,17 @@ static void run(void)
        pthread_t handler_thread;

        SAFE_PTHREAD_CREATE(&handler_thread, NULL,
-                           fault_handler_thread, NULL);
+                               fault_handler_thread, NULL);

        new_addr = mremap(old_addr, page_size, page_size,
-                         MREMAP_DONTUNMAP | MREMAP_MAYMOVE, NULL);
-
-       if (new_addr == MAP_FAILED) {
-               if (errno == EINVAL) {
-                       tst_brk(TCONF | TERRNO,
-                               "mremap with MREMAP_DONTUNMAP not supported?");
-               }
+                               MREMAP_DONTUNMAP | MREMAP_MAYMOVE, NULL);
+       if (new_addr == MAP_FAILED)
                tst_brk(TBROK | TERRNO, "mremap failed");
-       }

        tst_res(TINFO, "New mapping created at %p", (void *)new_addr);

        TST_EXP_EQ_STR(new_addr, TEST_STRING_A);
-       strcpy(new_addr, TEST_STRING_B);
+       memcpy(new_addr, TEST_STRING_B, sizeof(TEST_STRING_B));

        TST_CHECKPOINT_WAKE(0);

@@ -148,8 +152,7 @@ static void run(void)
        TST_EXP_EQ_STR(old_addr, TEST_STRING_B);

        SAFE_MUNMAP(new_addr, page_size);
-       new_addr = NULL;
-       strcpy(old_addr, TEST_STRING_A);
+       memcpy(old_addr, TEST_STRING_A, sizeof(TEST_STRING_A));
 }

 static struct tst_test test = {

-- 
Regards,
Li Wang

-- 
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