[PATCH -V2 1/7] migrate: fix syscall move_pages() return value for failure

Huang Ying
2022-07-11T08:50:08Z

The return value of move_pages() syscall is incorrect when counting
the remaining pages to be migrated. For example, for the following
test program,

"
#define _GNU_SOURCE

#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>

#include <fcntl.h>
#include <sys/uio.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <unistd.h>
#include <numaif.h>
#include <numa.h>

#ifndef MADV_FREE
#define MADV_FREE 8 /* free pages only if memory pressure */
#endif

#define ONE_MB (1024 * 1024)
#define MAP_SIZE (16 * ONE_MB)
#define THP_SIZE (2 * ONE_MB)
#define THP_MASK (THP_SIZE - 1)

#define ERR_EXIT_ON(cond, msg) \
do { \
int __cond_in_macro = (cond); \
if (__cond_in_macro) \
error_exit(__cond_in_macro, (msg)); \
} while (0)

void error_msg(int ret, int nr, int *status, const char *msg)
{
int i;

fprintf(stderr, "Error: %s, ret : %d, error: %s\n",
msg, ret, strerror(errno));

if (!nr)
return;
fprintf(stderr, "status: ");
for (i = 0; i < nr; i++)
fprintf(stderr, "%d ", status[i]);
fprintf(stderr, "\n");
}

void error_exit(int ret, const char *msg)
{
error_msg(ret, 0, NULL, msg);
exit(1);
}

int page_size;

bool do_vmsplice;
bool do_thp;

static int pipe_fds[2];
void *addr;
char *pn;
char *pn1;
void *pages[2];
int status[2];

void prepare()
{
int ret;
struct iovec iov;

if (addr) {
munmap(addr, MAP_SIZE);
close(pipe_fds[0]);
close(pipe_fds[1]);
}

ret = pipe(pipe_fds);
ERR_EXIT_ON(ret, "pipe");

addr = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
ERR_EXIT_ON(addr == MAP_FAILED, "mmap");
if (do_thp) {
ret = madvise(addr, MAP_SIZE, MADV_HUGEPAGE);
ERR_EXIT_ON(ret, "advise hugepage");
}

pn = (char *)(((unsigned long)addr + THP_SIZE) & ~THP_MASK);
pn1 = pn + THP_SIZE;
pages[0] = pn;
pages[1] = pn1;
*pn = 1;

if (do_vmsplice) {
iov.iov_base = pn;
iov.iov_len = page_size;
ret = vmsplice(pipe_fds[1], &iov, 1, 0);
ERR_EXIT_ON(ret < 0, "vmsplice");
}

status[0] = status[1] = 1024;
}

void test_migrate()
{
int ret;
int nodes[2] = { 1, 1 };
pid_t pid = getpid();

prepare();
ret = move_pages(pid, 1, pages, nodes, status, MPOL_MF_MOVE_ALL);
error_msg(ret, 1, status, "move 1 page");

prepare();
ret = move_pages(pid, 2, pages, nodes, status, MPOL_MF_MOVE_ALL);
error_msg(ret, 2, status, "move 2 pages, page 1 not mapped");

prepare();
*pn1 = 1;
ret = move_pages(pid, 2, pages, nodes, status, MPOL_MF_MOVE_ALL);
error_msg(ret, 2, status, "move 2 pages");

prepare();
*pn1 = 1;
nodes[1] = 0;
ret = move_pages(pid, 2, pages, nodes, status, MPOL_MF_MOVE_ALL);
error_msg(ret, 2, status, "move 2 pages, page 1 to node 0");
}

int main(int argc, char *argv[])
{
numa_run_on_node(0);
page_size = getpagesize();

test_migrate();

fprintf(stderr, "\nMake page 0 cannot be migrated:\n");
do_vmsplice = true;
test_migrate();

fprintf(stderr, "\nTest THP:\n");
do_thp = true;
do_vmsplice = false;
test_migrate();

fprintf(stderr, "\nTHP: make page 0 cannot be migrated:\n");
do_vmsplice = true;
test_migrate();

return 0;
}
"

The output of the current kernel is,

"
Error: move 1 page, ret : 0, error: Success
status: 1
Error: move 2 pages, page 1 not mapped, ret : 0, error: Success
status: 1 -14
Error: move 2 pages, ret : 0, error: Success
status: 1 1
Error: move 2 pages, page 1 to node 0, ret : 0, error: Success
status: 1 0

Make page 0 cannot be migrated:
Error: move 1 page, ret : 0, error: Success
status: 1024
Error: move 2 pages, page 1 not mapped, ret : 1, error: Success
status: 1024 -14
Error: move 2 pages, ret : 0, error: Success
status: 1024 1024
Error: move 2 pages, page 1 to node 0, ret : 1, error: Success
status: 1024 1024
"

While the expected output is,

"
Error: move 1 page, ret : 0, error: Success
status: 1
Error: move 2 pages, page 1 not mapped, ret : 0, error: Success
status: 1 -14
Error: move 2 pages, ret : 0, error: Success
status: 1 1
Error: move 2 pages, page 1 to node 0, ret : 0, error: Success
status: 1 0

Make page 0 cannot be migrated:
Error: move 1 page, ret : 1, error: Success
status: 1024
Error: move 2 pages, page 1 not mapped, ret : 1, error: Success
status: 1024 -14
Error: move 2 pages, ret : 1, error: Success
status: 1024 1024
Error: move 2 pages, page 1 to node 0, ret : 2, error: Success
status: 1024 1024
"

Fix this via correcting the remaining pages counting. With the fix,
the output for the test program as above is expected.

Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Fixes: 5984fabb6e82 ("mm: move_pages: report the number of non-attempted pages")
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Yang Shi <shy828301@gmail.com>
---
mm/migrate.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 6c1ea61f39d8..472335f0aaa3 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1682,7 +1682,7 @@ static int move_pages_and_store_status(struct mm_struct *mm, int node,
* well.
*/
if (err > 0)
- err += nr_pages - i - 1;
+ err += nr_pages - i;
return err;
}
return store_status(status, start, node, i - start);
@@ -1768,8 +1768,12 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,

err = move_pages_and_store_status(mm, current_node, &pagelist,
status, start, i, nr_pages);
- if (err)
+ if (err) {
+ /* We have stored status of page i */
+ if (err > 0)
+ err--;
goto out;
+ }
current_node = NUMA_NO_NODE;
}
out_flush:
--
2.30.2