[LTP] [PATCH v7] hugemmap: Migrate alloc-instantiate-race test from libhugetlbfs

[LTP] [PATCH v7] hugemmap: Migrate alloc-instantiate-race test from libhugetlbfs

[Samir Mulani]

Migrate the alloc-instantiate-race.c test from libhugetlbfs [1] to LTP
as hugemmap42.

This test is designed to detect a kernel allocation race introduced
with hugepage demand-faulting.  The problem is that no lock is held
between allocating a hugepage and instantiating it in the
pagetables or page cache index.  In between the two, the (huge)
page is cleared, so there's substantial time.  Thus two processes
can race instantiating the (same) last available hugepage - one
will fail on the allocation, and thus cause an OOM fault even
though the page it actually wants is being instantiated by the
other racing process.

[1] https://github.com/libhugetlbfs/libhugetlbfs/blob/master/tests/alloc-instantiate-race.c

Signed-off-by: Samir Mulani <samir@linux.ibm.com>
---
v7:
- Fix commit message: s/hugemmap36/hugemmap42/
- Add hugemmap42_private runtest entry to exercise the MAP_PRIVATE
  pthread path (-m private)
- Pass 0 instead of getpid() to sched_setaffinity() so each racer
  thread pins itself, not the thread-group leader
- Fault in all p_sync pages before run_race() so hugepages are
  actually consumed from the pool before the race starts
- Save sync_mapping_size at mmap() time and reuse it in cleanup()
  instead of re-reading MEMINFO_HPAGE_FREE
- Use {} instead of {NULL, NULL, NULL} as options array sentinel

Link: https://lore.kernel.org/all/20250928030721.3537869-1-samir@linux.ibm.com/ #v3
Link: https://lore.kernel.org/ltp/20260317095559.5766-1-samir@linux.ibm.com/ #v4
Link: https://lore.kernel.org/ltp/20260504132405.333588-1-samir@linux.ibm.com/ #v5
Link: https://lore.kernel.org/ltp/20260818143106.43797-1-samir@linux.ibm.com/ #v6

 runtest/hugetlb                               |   2 +
 testcases/kernel/mem/.gitignore               |   1 +
 .../kernel/mem/hugetlb/hugemmap/hugemmap42.c  | 317 ++++++++++++++++++
 3 files changed, 320 insertions(+)
 create mode 100644 testcases/kernel/mem/hugetlb/hugemmap/hugemmap42.c

diff --git a/runtest/hugetlb b/runtest/hugetlb
index 6b35c1f42..b7872368d 100644
--- a/runtest/hugetlb
+++ b/runtest/hugetlb
@@ -40,6 +40,8 @@ hugemmap35 hugemmap35
 hugemmap36 hugemmap36
 hugemmap37 hugemmap37
 hugemmap38 hugemmap38
+hugemmap42 hugemmap42
+hugemmap42_private hugemmap42 -m private
 hugemmap05_1 hugemmap05 -m
 hugemmap05_2 hugemmap05 -s
 hugemmap05_3 hugemmap05 -s -m
diff --git a/testcases/kernel/mem/.gitignore b/testcases/kernel/mem/.gitignore
index e63a6dde7..a0a877a58 100644
--- a/testcases/kernel/mem/.gitignore
+++ b/testcases/kernel/mem/.gitignore
@@ -40,6 +40,7 @@
 /hugetlb/hugemmap/hugemmap36
 /hugetlb/hugemmap/hugemmap37
 /hugetlb/hugemmap/hugemmap38
+/hugetlb/hugemmap/hugemmap42
 /hugetlb/hugeshmat/hugeshmat01
 /hugetlb/hugeshmat/hugeshmat02
 /hugetlb/hugeshmat/hugeshmat03
diff --git a/testcases/kernel/mem/hugetlb/hugemmap/hugemmap42.c b/testcases/kernel/mem/hugetlb/hugemmap/hugemmap42.c
new file mode 100644
index 000000000..901ea07ab
--- /dev/null
+++ b/testcases/kernel/mem/hugetlb/hugemmap/hugemmap42.c
@@ -0,0 +1,317 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2005-2006, 2026 IBM Corporation
+ * Author: David Gibson & Adam Litke
+ */
+
+/*\
+ * This test is designed to detect a kernel allocation race introduced
+ * with hugepage demand-faulting.  The problem is that no lock is held
+ * between allocating a hugepage and instantiating it in the
+ * pagetables or page cache index.  In between the two, the (huge)
+ * page is cleared, so there's substantial time.  Thus two processes
+ * can race instantiating the (same) last available hugepage - one
+ * will fail on the allocation, and thus cause an OOM fault even
+ * though the page it actually wants is being instantiated by the
+ * other racing process.
+ */
+
+#define _GNU_SOURCE
+#include <pthread.h>
+#include "tst_test.h"
+#include "tst_safe_pthread.h"
+#include "hugetlb.h"
+
+#define MNTPOINT "hugetlbfs/"
+
+static char *str_op;
+static int child1, child2, race_type;
+static int fd_sync = -1;
+static int fd_race = -1;
+static void *p_race = MAP_FAILED;
+static void *p_sync = MAP_FAILED;
+static size_t sync_mapping_size;
+
+struct racer_info {
+	void *p;
+	int cpu;
+	int status;
+};
+
+static int one_racer(void *p, int cpu)
+{
+	volatile int *pi = p;
+	cpu_set_t *cpuset;
+	size_t mask_size;
+	int err;
+
+	cpuset = CPU_ALLOC(cpu + 1);
+	if (!cpuset)
+		tst_brk(TBROK | TERRNO, "CPU_ALLOC() failed");
+
+	mask_size = CPU_ALLOC_SIZE(cpu + 1);
+
+	/* Split onto different CPUs to encourage the race */
+	CPU_ZERO_S(mask_size, cpuset);
+	CPU_SET_S(cpu, mask_size, cpuset);
+
+	/*
+	 * Use pid 0 so that sched_setaffinity() applies to the calling
+	 * thread rather than the thread-group leader.  getpid() returns
+	 * the same TGID for every pthread in the process, so passing it
+	 * would pin the main thread instead of the racer.
+	 */
+	err = sched_setaffinity(0, mask_size, cpuset);
+	CPU_FREE(cpuset);
+	if (err == -1)
+		tst_brk(TBROK | TERRNO, "sched_setaffinity() failed");
+
+	/* Wait for parent to signal both racers to start */
+	TST_CHECKPOINT_WAIT(0);
+
+	/* Fault in the hugepage - triggers the race */
+	*pi = 1;
+
+	return 0;
+}
+
+static void proc_racer(void *p, int cpu)
+{
+	exit(one_racer(p, cpu));
+}
+
+static void *thread_racer(void *info)
+{
+	struct racer_info *ri = info;
+
+	ri->status = one_racer(ri->p, ri->cpu);
+	return ri;
+}
+
+static void check_online_cpus(int online_cpus[], int nr_cpus_needed)
+{
+	cpu_set_t cpuset;
+	int total_cpus, cpu_idx;
+
+	CPU_ZERO(&cpuset);
+
+	total_cpus = get_nprocs_conf();
+
+	if (sched_getaffinity(0, sizeof(cpu_set_t), &cpuset) == -1)
+		tst_brk(TBROK | TERRNO, "sched_getaffinity() failed");
+
+	tst_res(TINFO, "Online CPUs needed: %d, available: %d",
+		nr_cpus_needed, CPU_COUNT(&cpuset));
+
+	if (CPU_COUNT(&cpuset) < nr_cpus_needed)
+		tst_brk(TCONF, "At least %d online CPUs are required",
+			nr_cpus_needed);
+
+	cpu_idx = 0;
+	for (int i = 0; i < total_cpus && cpu_idx < nr_cpus_needed; i++) {
+		if (CPU_ISSET(i, &cpuset))
+			online_cpus[cpu_idx++] = i;
+	}
+
+	if (cpu_idx < nr_cpus_needed)
+		tst_brk(TBROK, "Unable to find enough online CPUs");
+}
+
+static void run_race(int rtype)
+{
+	void *tret1, *tret2;
+	int status1 = 0, status2 = 0;
+	int online_cpus[2];
+	long hpage_size;
+	pthread_t thread1, thread2;
+
+	check_online_cpus(online_cpus, 2);
+
+	hpage_size = tst_get_hugepage_size();
+
+	/* Get a new file for the final page */
+	fd_race = tst_creat_unlinked(MNTPOINT, 0, 0600);
+	tst_res(TINFO, "Mapping final page..");
+
+	p_race = SAFE_MMAP(NULL, hpage_size, PROT_READ | PROT_WRITE,
+			   rtype, fd_race, 0);
+
+	if (rtype == MAP_SHARED) {
+		child1 = SAFE_FORK();
+		if (child1 == 0)
+			proc_racer(p_race, online_cpus[0]);
+
+		child2 = SAFE_FORK();
+		if (child2 == 0)
+			proc_racer(p_race, online_cpus[1]);
+
+		/* Wake both children to start the race simultaneously */
+		TST_CHECKPOINT_WAKE2(0, 2);
+
+		SAFE_WAITPID(child1, &status1, 0);
+		child1 = 0;
+		tst_res(TINFO, "Child 1 status: %x", status1);
+
+		SAFE_WAITPID(child2, &status2, 0);
+		child2 = 0;
+		tst_res(TINFO, "Child 2 status: %x", status2);
+
+		if (WIFSIGNALED(status1))
+			tst_res(TFAIL, "Child 1 killed by signal %s",
+				strsignal(WTERMSIG(status1)));
+		if (WIFSIGNALED(status2))
+			tst_res(TFAIL, "Child 2 killed by signal %s",
+				strsignal(WTERMSIG(status2)));
+	} else {
+		struct racer_info ri1 = {
+			.p = p_race,
+			.cpu = online_cpus[0],
+			.status = -1,
+		};
+		struct racer_info ri2 = {
+			.p = p_race,
+			.cpu = online_cpus[1],
+			.status = -1,
+		};
+
+		SAFE_PTHREAD_CREATE(&thread1, NULL, thread_racer, &ri1);
+		SAFE_PTHREAD_CREATE(&thread2, NULL, thread_racer, &ri2);
+
+		/* Wake both threads to start the race simultaneously */
+		TST_CHECKPOINT_WAKE2(0, 2);
+
+		SAFE_PTHREAD_JOIN(thread1, &tret1);
+		if (tret1 != &ri1)
+			tst_res(TFAIL, "Thread 1 returned %p not %p, killed?",
+				tret1, &ri1);
+
+		SAFE_PTHREAD_JOIN(thread2, &tret2);
+		if (tret2 != &ri2)
+			tst_res(TFAIL, "Thread 2 returned %p not %p, killed?",
+				tret2, &ri2);
+
+		status1 = ri1.status;
+		status2 = ri2.status;
+	}
+
+	if (status1 != 0)
+		tst_res(TFAIL, "Racer 1 terminated with code %d", status1);
+
+	if (status2 != 0)
+		tst_res(TFAIL, "Racer 2 terminated with code %d", status2);
+
+	if (status1 == 0 && status2 == 0)
+		tst_res(TPASS, "Test completed successfully");
+
+	SAFE_MUNMAP(p_race, hpage_size);
+	p_race = MAP_FAILED;
+
+	SAFE_CLOSE(fd_race);
+	fd_race = -1;
+}
+
+static void run_test(void)
+{
+	unsigned long totpages;
+	long hpage_size;
+
+	totpages = SAFE_READ_MEMINFO(MEMINFO_HPAGE_FREE);
+	if (totpages < 2)
+		tst_brk(TCONF, "Not enough free hugepages, need at least 2");
+
+	hpage_size = tst_get_hugepage_size();
+
+	tst_res(TINFO, "Instantiating..");
+
+	fd_sync = tst_creat_unlinked(MNTPOINT, 0, 0600);
+
+	tst_res(TINFO, "Mapping %lu/%lu pages..", totpages - 1, totpages);
+	sync_mapping_size = (totpages - 1) * hpage_size;
+	p_sync = SAFE_MMAP(NULL, sync_mapping_size,
+			   PROT_READ | PROT_WRITE, MAP_SHARED, fd_sync, 0);
+
+	/*
+	 * Fault in every sync page to consume them from the hugepage pool.
+	 * Without touching each page, mmap() does not allocate hugepages
+	 * (no MAP_POPULATE), so all free hugepages remain available to the
+	 * racers and the allocation race is never exercised.
+	 */
+	for (unsigned long i = 0; i < totpages - 1; i++) {
+		volatile char *cp = (volatile char *)p_sync + i * hpage_size;
+
+		*cp = 0;
+	}
+
+	run_race(race_type);
+
+	SAFE_MUNMAP(p_sync, sync_mapping_size);
+	p_sync = MAP_FAILED;
+
+	SAFE_CLOSE(fd_sync);
+	fd_sync = -1;
+}
+
+static void setup(void)
+{
+	if (str_op) {
+		if (strcmp(str_op, "shared") == 0)
+			race_type = MAP_SHARED;
+		else if (strcmp(str_op, "private") == 0)
+			race_type = MAP_PRIVATE;
+		else
+			tst_brk(TBROK,
+				"Invalid parameter: use -m <private|shared>");
+	} else {
+		/* Default to shared if no option is passed */
+		race_type = MAP_SHARED;
+	}
+}
+
+static void cleanup(void)
+{
+	if (p_race != MAP_FAILED)
+		SAFE_MUNMAP(p_race, tst_get_hugepage_size());
+
+	if (fd_race >= 0)
+		SAFE_CLOSE(fd_race);
+
+	/*
+	 * Use the saved sync_mapping_size rather than re-reading
+	 * MEMINFO_HPAGE_FREE: the current free count differs from the
+	 * mapping length and could cause munmap() to remove an adjacent
+	 * mapping or leave part of p_sync mapped.
+	 */
+	if (p_sync != MAP_FAILED)
+		SAFE_MUNMAP(p_sync, sync_mapping_size);
+
+	if (fd_sync >= 0)
+		SAFE_CLOSE(fd_sync);
+
+	if (child1 > 0) {
+		if (kill(child1, 0) == 0)
+			SAFE_KILL(child1, SIGKILL);
+	}
+
+	if (child2 > 0) {
+		if (kill(child2, 0) == 0)
+			SAFE_KILL(child2, SIGKILL);
+	}
+}
+
+static struct tst_test test = {
+	.options = (struct tst_option[]) {
+		{"m:", &str_op, "Type of mmap() mapping <private|shared>"},
+		{}
+	},
+	.needs_root = 1,
+	.mntpoint = MNTPOINT,
+	.needs_hugetlbfs = 1,
+	.needs_tmpdir = 1,
+	.setup = setup,
+	.cleanup = cleanup,
+	.test_all = run_test,
+	.hugepages = {2, TST_NEEDS},
+	.forks_child = 1,
+	.needs_checkpoints = 1,
+	.min_cpus = 2,
+};
-- 
2.52.0


-- 
Mailing list info: https://lists.linux.it/listinfo/ltp

Re: [LTP] hugemmap: Migrate alloc-instantiate-race test from libhugetlbfs

[linuxtestproject.agent]

Hi Samir,

On Aug 21, 2026, Samir Mulani wrote:
> hugemmap: Migrate alloc-instantiate-race test from libhugetlbfs

> +		SAFE_PTHREAD_CREATE(&thread1, NULL, thread_racer, &ri1);
> +		SAFE_PTHREAD_CREATE(&thread2, NULL, thread_racer, &ri2);
> +
> +		/* Wake both threads to start the race simultaneously */
> +		TST_CHECKPOINT_WAKE2(0, 2);

Medium: Could the MAP_PRIVATE pthread race run in a child process so that
the parent can translate SIGBUS into TFAIL?

The allocation failure under test makes hugetlb_no_page() return
VM_FAULT_SIGBUS. An unhandled SIGBUS in either thread terminates the whole
thread group, after which LTP's check_child_status() reports TBROK instead
of identifying the kernel regression as TFAIL. The MAP_SHARED variant
already translates signal deaths in its child racers.

> +	cpu_set_t cpuset;
> +	int total_cpus, cpu_idx;
> +
> +	CPU_ZERO(&cpuset);
> +
> +	total_cpus = get_nprocs_conf();
> +
> +	if (sched_getaffinity(0, sizeof(cpu_set_t), &cpuset) == -1)
> +		tst_brk(TBROK | TERRNO, "sched_getaffinity() failed");

Medium: Could this use a dynamic mask sized with tst_ncpus_max(),
CPU_ALLOC(), and CPU_ALLOC_SIZE()?

sched_getaffinity() returns EINVAL when the supplied buffer is smaller
than the kernel affinity mask. A kernel supporting more than CPU_SETSIZE
CPUs therefore produces TBROK even when the test has two usable CPUs.

> +#include <pthread.h>
> +#include "tst_test.h"
> +#include "tst_safe_pthread.h"

Medium: Could hugemmap42 be added to the Makefile's existing
CFLAGS += -pthread rule?

The test links on modern glibc because libpthread was merged into libc,
but older supported libc versions need -pthread to resolve the symbols
used by the safe pthread wrappers.

> +/hugetlb/hugemmap/hugemmap42

Low: Could this entry be moved to a leaf
testcases/kernel/mem/hugetlb/hugemmap/.gitignore?

New test binaries should be ignored in their own test directory rather
than in testcases/kernel/mem/.gitignore.

> +	.hugepages = {2, TST_NEEDS},
> +	.forks_child = 1,
> +	.needs_checkpoints = 1,
> +	.min_cpus = 2,
> +};

Low: Could the kernel fix for this regression be added as a linux-git
tag so that failures provide the missing-fix hint?

> + * other racing process.
> + */
> [...]
> +	.needs_root = 1,

Low: Could the exported description explain that root is needed to
reserve hugepages and mount hugetlbfs?

> +	SAFE_CLOSE(fd_race);
> +	fd_race = -1;
> [...]
> +	if (fd_race >= 0)
> +		SAFE_CLOSE(fd_race);

Low: Could the redundant assignment be removed and the cleanup guard use
fd_race != -1, with the same changes for fd_sync?

SAFE_CLOSE() already sets the descriptor to -1, and != -1 is the LTP
descriptor-validity convention.

Verdict - Needs revision

---
Note:

The agent can sometimes produce false positives although often its
findings are genuine. If you find issues with the review, please
comment this email or ignore the suggestions.

Regards,
LTP AI Reviewer

-- 
Mailing list info: https://lists.linux.it/listinfo/ltp

Re: [LTP] [PATCH v7] hugemmap: Migrate alloc-instantiate-race test from libhugetlbfs

[Cyril Hrubis]

Hi!
> This test is designed to detect a kernel allocation race introduced
> with hugepage demand-faulting.  The problem is that no lock is held
> between allocating a hugepage and instantiating it in the
> pagetables or page cache index.  In between the two, the (huge)
> page is cleared, so there's substantial time.  Thus two processes
> can race instantiating the (same) last available hugepage - one
> will fail on the allocation, and thus cause an OOM fault even
> though the page it actually wants is being instantiated by the
> other racing process.
> 
> [1] https://github.com/libhugetlbfs/libhugetlbfs/blob/master/tests/alloc-instantiate-race.c
> 
> Signed-off-by: Samir Mulani <samir@linux.ibm.com>
> ---
> v7:
> - Fix commit message: s/hugemmap36/hugemmap42/
> - Add hugemmap42_private runtest entry to exercise the MAP_PRIVATE
>   pthread path (-m private)
> - Pass 0 instead of getpid() to sched_setaffinity() so each racer
>   thread pins itself, not the thread-group leader
> - Fault in all p_sync pages before run_race() so hugepages are
>   actually consumed from the pool before the race starts
> - Save sync_mapping_size at mmap() time and reuse it in cleanup()
>   instead of re-reading MEMINFO_HPAGE_FREE
> - Use {} instead of {NULL, NULL, NULL} as options array sentinel
> 
> Link: https://lore.kernel.org/all/20250928030721.3537869-1-samir@linux.ibm.com/ #v3
> Link: https://lore.kernel.org/ltp/20260317095559.5766-1-samir@linux.ibm.com/ #v4
> Link: https://lore.kernel.org/ltp/20260504132405.333588-1-samir@linux.ibm.com/ #v5
> Link: https://lore.kernel.org/ltp/20260818143106.43797-1-samir@linux.ibm.com/ #v6
> 
>  runtest/hugetlb                               |   2 +
>  testcases/kernel/mem/.gitignore               |   1 +
>  .../kernel/mem/hugetlb/hugemmap/hugemmap42.c  | 317 ++++++++++++++++++
>  3 files changed, 320 insertions(+)
>  create mode 100644 testcases/kernel/mem/hugetlb/hugemmap/hugemmap42.c
> 
> diff --git a/runtest/hugetlb b/runtest/hugetlb
> index 6b35c1f42..b7872368d 100644
> --- a/runtest/hugetlb
> +++ b/runtest/hugetlb
> @@ -40,6 +40,8 @@ hugemmap35 hugemmap35
>  hugemmap36 hugemmap36
>  hugemmap37 hugemmap37
>  hugemmap38 hugemmap38
> +hugemmap42 hugemmap42
> +hugemmap42_private hugemmap42 -m private

This is ugly. The modern way how to run two subtests in LTP is to set
.tcnt = 2 and switch on the index in the run() function.

>  hugemmap05_1 hugemmap05 -m
>  hugemmap05_2 hugemmap05 -s
>  hugemmap05_3 hugemmap05 -s -m
> diff --git a/testcases/kernel/mem/.gitignore b/testcases/kernel/mem/.gitignore
> index e63a6dde7..a0a877a58 100644
> --- a/testcases/kernel/mem/.gitignore
> +++ b/testcases/kernel/mem/.gitignore
> @@ -40,6 +40,7 @@
>  /hugetlb/hugemmap/hugemmap36
>  /hugetlb/hugemmap/hugemmap37
>  /hugetlb/hugemmap/hugemmap38
> +/hugetlb/hugemmap/hugemmap42
>  /hugetlb/hugeshmat/hugeshmat01
>  /hugetlb/hugeshmat/hugeshmat02
>  /hugetlb/hugeshmat/hugeshmat03
> diff --git a/testcases/kernel/mem/hugetlb/hugemmap/hugemmap42.c b/testcases/kernel/mem/hugetlb/hugemmap/hugemmap42.c
> new file mode 100644
> index 000000000..901ea07ab
> --- /dev/null
> +++ b/testcases/kernel/mem/hugetlb/hugemmap/hugemmap42.c
> @@ -0,0 +1,317 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (C) 2005-2006, 2026 IBM Corporation
> + * Author: David Gibson & Adam Litke
> + */
> +
> +/*\
> + * This test is designed to detect a kernel allocation race introduced
> + * with hugepage demand-faulting.  The problem is that no lock is held
> + * between allocating a hugepage and instantiating it in the
> + * pagetables or page cache index.  In between the two, the (huge)
> + * page is cleared, so there's substantial time.  Thus two processes
> + * can race instantiating the (same) last available hugepage - one
> + * will fail on the allocation, and thus cause an OOM fault even
> + * though the page it actually wants is being instantiated by the
> + * other racing process.
> + */

That sounds like a regression test, do we have a kernel commit for the
fix for the race?

> +#define _GNU_SOURCE
> +#include <pthread.h>
> +#include "tst_test.h"
> +#include "tst_safe_pthread.h"
> +#include "hugetlb.h"
> +
> +#define MNTPOINT "hugetlbfs/"
> +
> +static char *str_op;
> +static int child1, child2, race_type;
> +static int fd_sync = -1;
> +static int fd_race = -1;
> +static void *p_race = MAP_FAILED;
> +static void *p_sync = MAP_FAILED;
> +static size_t sync_mapping_size;
> +
> +struct racer_info {
> +	void *p;
> +	int cpu;
> +	int status;
> +};
> +
> +static int one_racer(void *p, int cpu)
> +{
> +	volatile int *pi = p;
> +	cpu_set_t *cpuset;
> +	size_t mask_size;
> +	int err;
> +
> +	cpuset = CPU_ALLOC(cpu + 1);
> +	if (!cpuset)
> +		tst_brk(TBROK | TERRNO, "CPU_ALLOC() failed");
> +
> +	mask_size = CPU_ALLOC_SIZE(cpu + 1);
> +
> +	/* Split onto different CPUs to encourage the race */
> +	CPU_ZERO_S(mask_size, cpuset);
> +	CPU_SET_S(cpu, mask_size, cpuset);
> +
> +	/*
> +	 * Use pid 0 so that sched_setaffinity() applies to the calling
> +	 * thread rather than the thread-group leader.  getpid() returns
> +	 * the same TGID for every pthread in the process, so passing it
> +	 * would pin the main thread instead of the racer.
> +	 */
> +	err = sched_setaffinity(0, mask_size, cpuset);
> +	CPU_FREE(cpuset);
> +	if (err == -1)
> +		tst_brk(TBROK | TERRNO, "sched_setaffinity() failed");
> +
> +	/* Wait for parent to signal both racers to start */
> +	TST_CHECKPOINT_WAIT(0);
> +
> +	/* Fault in the hugepage - triggers the race */
> +	*pi = 1;

If this is the actual race, it would probably make sense to actually
unmap/map and fault the page in a loop. We do have a tst_fuzzy_sync.h
that has a machinery for synchronizing two processes to hit a race.
Maybe it would make sense to use it.

> +	return 0;
> +}
> +
> +static void proc_racer(void *p, int cpu)
> +{
> +	exit(one_racer(p, cpu));
> +}
> +
> +static void *thread_racer(void *info)
> +{
> +	struct racer_info *ri = info;
> +
> +	ri->status = one_racer(ri->p, ri->cpu);
> +	return ri;
> +}
> +
> +static void check_online_cpus(int online_cpus[], int nr_cpus_needed)
> +{
> +	cpu_set_t cpuset;
> +	int total_cpus, cpu_idx;
> +
> +	CPU_ZERO(&cpuset);
> +
> +	total_cpus = get_nprocs_conf();
> +
> +	if (sched_getaffinity(0, sizeof(cpu_set_t), &cpuset) == -1)
> +		tst_brk(TBROK | TERRNO, "sched_getaffinity() failed");
> +
> +	tst_res(TINFO, "Online CPUs needed: %d, available: %d",
> +		nr_cpus_needed, CPU_COUNT(&cpuset));
> +
> +	if (CPU_COUNT(&cpuset) < nr_cpus_needed)
> +		tst_brk(TCONF, "At least %d online CPUs are required",
> +			nr_cpus_needed);
> +
> +	cpu_idx = 0;
> +	for (int i = 0; i < total_cpus && cpu_idx < nr_cpus_needed; i++) {
> +		if (CPU_ISSET(i, &cpuset))
> +			online_cpus[cpu_idx++] = i;
> +	}
> +
> +	if (cpu_idx < nr_cpus_needed)
> +		tst_brk(TBROK, "Unable to find enough online CPUs");
> +}
> +
> +static void run_race(int rtype)
> +{
> +	void *tret1, *tret2;
> +	int status1 = 0, status2 = 0;
> +	int online_cpus[2];
> +	long hpage_size;
> +	pthread_t thread1, thread2;
> +
> +	check_online_cpus(online_cpus, 2);
> +
> +	hpage_size = tst_get_hugepage_size();
> +
> +	/* Get a new file for the final page */
> +	fd_race = tst_creat_unlinked(MNTPOINT, 0, 0600);
> +	tst_res(TINFO, "Mapping final page..");
> +
> +	p_race = SAFE_MMAP(NULL, hpage_size, PROT_READ | PROT_WRITE,
> +			   rtype, fd_race, 0);
> +
> +	if (rtype == MAP_SHARED) {
> +		child1 = SAFE_FORK();
> +		if (child1 == 0)
> +			proc_racer(p_race, online_cpus[0]);
> +
> +		child2 = SAFE_FORK();
> +		if (child2 == 0)
> +			proc_racer(p_race, online_cpus[1]);
> +
> +		/* Wake both children to start the race simultaneously */
> +		TST_CHECKPOINT_WAKE2(0, 2);
> +
> +		SAFE_WAITPID(child1, &status1, 0);
> +		child1 = 0;
> +		tst_res(TINFO, "Child 1 status: %x", status1);
> +
> +		SAFE_WAITPID(child2, &status2, 0);
> +		child2 = 0;
> +		tst_res(TINFO, "Child 2 status: %x", status2);
> +
> +		if (WIFSIGNALED(status1))
> +			tst_res(TFAIL, "Child 1 killed by signal %s",
> +				strsignal(WTERMSIG(status1)));
> +		if (WIFSIGNALED(status2))
> +			tst_res(TFAIL, "Child 2 killed by signal %s",
> +				strsignal(WTERMSIG(status2)));
> +	} else {
> +		struct racer_info ri1 = {
> +			.p = p_race,
> +			.cpu = online_cpus[0],
> +			.status = -1,
> +		};
> +		struct racer_info ri2 = {
> +			.p = p_race,
> +			.cpu = online_cpus[1],
> +			.status = -1,
> +		};
> +
> +		SAFE_PTHREAD_CREATE(&thread1, NULL, thread_racer, &ri1);
> +		SAFE_PTHREAD_CREATE(&thread2, NULL, thread_racer, &ri2);
> +
> +		/* Wake both threads to start the race simultaneously */
> +		TST_CHECKPOINT_WAKE2(0, 2);
> +
> +		SAFE_PTHREAD_JOIN(thread1, &tret1);
> +		if (tret1 != &ri1)
> +			tst_res(TFAIL, "Thread 1 returned %p not %p, killed?",
> +				tret1, &ri1);
> +
> +		SAFE_PTHREAD_JOIN(thread2, &tret2);
> +		if (tret2 != &ri2)
> +			tst_res(TFAIL, "Thread 2 returned %p not %p, killed?",
> +				tret2, &ri2);
> +
> +		status1 = ri1.status;
> +		status2 = ri2.status;

Here the ri1.status and ri2.status is completely bogus, since that
either stays initialize to -1 or is set to 0 by clean exit of the
functions. Since the description says that the bug triggers OOM all
threads of the process would be killed if we reproduce the bug and we
will never get to this place anyways.

I suppose that you need to actually fork and then run the two threads in
the forked process in order to isolate it from the main test process.



Also the two different test modes does not have nearly any code in
common, so these two should be in two different functions.

> +	}
> +
> +	if (status1 != 0)
> +		tst_res(TFAIL, "Racer 1 terminated with code %d", status1);
> +
> +	if (status2 != 0)
> +		tst_res(TFAIL, "Racer 2 terminated with code %d", status2);
> +
> +	if (status1 == 0 && status2 == 0)
> +		tst_res(TPASS, "Test completed successfully");
> +
> +	SAFE_MUNMAP(p_race, hpage_size);
> +	p_race = MAP_FAILED;
> +
> +	SAFE_CLOSE(fd_race);
> +	fd_race = -1;
> +}
> +
> +static void run_test(void)
> +{
> +	unsigned long totpages;
> +	long hpage_size;
> +
> +	totpages = SAFE_READ_MEMINFO(MEMINFO_HPAGE_FREE);
> +	if (totpages < 2)
> +		tst_brk(TCONF, "Not enough free hugepages, need at least 2");

This is done by the .hugepages = {2, TST_NEEDS} in the tst_test
structure.

> +	hpage_size = tst_get_hugepage_size();
> +
> +	tst_res(TINFO, "Instantiating..");
> +
> +	fd_sync = tst_creat_unlinked(MNTPOINT, 0, 0600);
> +
> +	tst_res(TINFO, "Mapping %lu/%lu pages..", totpages - 1, totpages);
> +	sync_mapping_size = (totpages - 1) * hpage_size;
> +	p_sync = SAFE_MMAP(NULL, sync_mapping_size,
> +			   PROT_READ | PROT_WRITE, MAP_SHARED, fd_sync, 0);
> +
> +	/*
> +	 * Fault in every sync page to consume them from the hugepage pool.
> +	 * Without touching each page, mmap() does not allocate hugepages
> +	 * (no MAP_POPULATE), so all free hugepages remain available to the
> +	 * racers and the allocation race is never exercised.
> +	 */
> +	for (unsigned long i = 0; i < totpages - 1; i++) {
> +		volatile char *cp = (volatile char *)p_sync + i * hpage_size;
> +
> +		*cp = 0;
> +	}
> +
> +	run_race(race_type);
> +
> +	SAFE_MUNMAP(p_sync, sync_mapping_size);
> +	p_sync = MAP_FAILED;
> +
> +	SAFE_CLOSE(fd_sync);
> +	fd_sync = -1;

The fd is set to -1 by the SAFE_CLOSE()

> +}
> +
> +static void setup(void)
> +{
> +	if (str_op) {
> +		if (strcmp(str_op, "shared") == 0)
> +			race_type = MAP_SHARED;
> +		else if (strcmp(str_op, "private") == 0)
> +			race_type = MAP_PRIVATE;
> +		else
> +			tst_brk(TBROK,
> +				"Invalid parameter: use -m <private|shared>");
> +	} else {
> +		/* Default to shared if no option is passed */
> +		race_type = MAP_SHARED;
> +	}
> +}
> +
> +static void cleanup(void)
> +{
> +	if (p_race != MAP_FAILED)
> +		SAFE_MUNMAP(p_race, tst_get_hugepage_size());
> +
> +	if (fd_race >= 0)

fd_race != -1

> +		SAFE_CLOSE(fd_race);
> +
> +	/*
> +	 * Use the saved sync_mapping_size rather than re-reading
> +	 * MEMINFO_HPAGE_FREE: the current free count differs from the
> +	 * mapping length and could cause munmap() to remove an adjacent
> +	 * mapping or leave part of p_sync mapped.
> +	 */
> +	if (p_sync != MAP_FAILED)
> +		SAFE_MUNMAP(p_sync, sync_mapping_size);
> +
> +	if (fd_sync >= 0)
> +		SAFE_CLOSE(fd_sync);
> +
> +	if (child1 > 0) {
> +		if (kill(child1, 0) == 0)
> +			SAFE_KILL(child1, SIGKILL);
> +	}
> +
> +	if (child2 > 0) {
> +		if (kill(child2, 0) == 0)
> +			SAFE_KILL(child2, SIGKILL);
> +	}
> +}
> +
> +static struct tst_test test = {
> +	.options = (struct tst_option[]) {
> +		{"m:", &str_op, "Type of mmap() mapping <private|shared>"},
> +		{}
> +	},
> +	.needs_root = 1,
> +	.mntpoint = MNTPOINT,
> +	.needs_hugetlbfs = 1,
> +	.needs_tmpdir = 1,
> +	.setup = setup,
> +	.cleanup = cleanup,
> +	.test_all = run_test,
> +	.hugepages = {2, TST_NEEDS},
> +	.forks_child = 1,
> +	.needs_checkpoints = 1,
> +	.min_cpus = 2,
> +};
> -- 
> 2.52.0
> 

-- 
Cyril Hrubis
chrubis@suse.cz

-- 
Mailing list info: https://lists.linux.it/listinfo/ltp

Re: [LTP] [PATCH v7] hugemmap: Migrate alloc-instantiate-race test from libhugetlbfs

[samir]

Hello Cyril

On 31/08/26 7:04 pm, Cyril Hrubis wrote:
> Hi!
>> This test is designed to detect a kernel allocation race introduced
>> with hugepage demand-faulting.  The problem is that no lock is held
>> between allocating a hugepage and instantiating it in the
>> pagetables or page cache index.  In between the two, the (huge)
>> page is cleared, so there's substantial time.  Thus two processes
>> can race instantiating the (same) last available hugepage - one
>> will fail on the allocation, and thus cause an OOM fault even
>> though the page it actually wants is being instantiated by the
>> other racing process.
>>
>> [1] https://github.com/libhugetlbfs/libhugetlbfs/blob/master/tests/alloc-instantiate-race.c
>>
>> Signed-off-by: Samir Mulani <samir@linux.ibm.com>
>> ---
>> v7:
>> - Fix commit message: s/hugemmap36/hugemmap42/
>> - Add hugemmap42_private runtest entry to exercise the MAP_PRIVATE
>>    pthread path (-m private)
>> - Pass 0 instead of getpid() to sched_setaffinity() so each racer
>>    thread pins itself, not the thread-group leader
>> - Fault in all p_sync pages before run_race() so hugepages are
>>    actually consumed from the pool before the race starts
>> - Save sync_mapping_size at mmap() time and reuse it in cleanup()
>>    instead of re-reading MEMINFO_HPAGE_FREE
>> - Use {} instead of {NULL, NULL, NULL} as options array sentinel
>>
>> Link: https://lore.kernel.org/all/20250928030721.3537869-1-samir@linux.ibm.com/ #v3
>> Link: https://lore.kernel.org/ltp/20260317095559.5766-1-samir@linux.ibm.com/ #v4
>> Link: https://lore.kernel.org/ltp/20260504132405.333588-1-samir@linux.ibm.com/ #v5
>> Link: https://lore.kernel.org/ltp/20260818143106.43797-1-samir@linux.ibm.com/ #v6
>>
>>   runtest/hugetlb                               |   2 +
>>   testcases/kernel/mem/.gitignore               |   1 +
>>   .../kernel/mem/hugetlb/hugemmap/hugemmap42.c  | 317 ++++++++++++++++++
>>   3 files changed, 320 insertions(+)
>>   create mode 100644 testcases/kernel/mem/hugetlb/hugemmap/hugemmap42.c
>>
>> diff --git a/runtest/hugetlb b/runtest/hugetlb
>> index 6b35c1f42..b7872368d 100644
>> --- a/runtest/hugetlb
>> +++ b/runtest/hugetlb
>> @@ -40,6 +40,8 @@ hugemmap35 hugemmap35
>>   hugemmap36 hugemmap36
>>   hugemmap37 hugemmap37
>>   hugemmap38 hugemmap38
>> +hugemmap42 hugemmap42
>> +hugemmap42_private hugemmap42 -m private
> This is ugly. The modern way how to run two subtests in LTP is to set
> .tcnt = 2 and switch on the index in the run() function.
Will fix in the next version. Will remove the hugemmap42_private runtest 
entry and the -m option, and use .tcnt = 2 with .test = 
run_test(unsigned int n) switching on n instead.
>>   hugemmap05_1 hugemmap05 -m
>>   hugemmap05_2 hugemmap05 -s
>>   hugemmap05_3 hugemmap05 -s -m
>> diff --git a/testcases/kernel/mem/.gitignore b/testcases/kernel/mem/.gitignore
>> index e63a6dde7..a0a877a58 100644
>> --- a/testcases/kernel/mem/.gitignore
>> +++ b/testcases/kernel/mem/.gitignore
>> @@ -40,6 +40,7 @@
>>   /hugetlb/hugemmap/hugemmap36
>>   /hugetlb/hugemmap/hugemmap37
>>   /hugetlb/hugemmap/hugemmap38
>> +/hugetlb/hugemmap/hugemmap42
>>   /hugetlb/hugeshmat/hugeshmat01
>>   /hugetlb/hugeshmat/hugeshmat02
>>   /hugetlb/hugeshmat/hugeshmat03
>> diff --git a/testcases/kernel/mem/hugetlb/hugemmap/hugemmap42.c b/testcases/kernel/mem/hugetlb/hugemmap/hugemmap42.c
>> new file mode 100644
>> index 000000000..901ea07ab
>> --- /dev/null
>> +++ b/testcases/kernel/mem/hugetlb/hugemmap/hugemmap42.c
>> @@ -0,0 +1,317 @@
>> +// SPDX-License-Identifier: GPL-2.0-or-later
>> +/*
>> + * Copyright (C) 2005-2006, 2026 IBM Corporation
>> + * Author: David Gibson & Adam Litke
>> + */
>> +
>> +/*\
>> + * This test is designed to detect a kernel allocation race introduced
>> + * with hugepage demand-faulting.  The problem is that no lock is held
>> + * between allocating a hugepage and instantiating it in the
>> + * pagetables or page cache index.  In between the two, the (huge)
>> + * page is cleared, so there's substantial time.  Thus two processes
>> + * can race instantiating the (same) last available hugepage - one
>> + * will fail on the allocation, and thus cause an OOM fault even
>> + * though the page it actually wants is being instantiated by the
>> + * other racing process.
>> + */
> That sounds like a regression test, do we have a kernel commit for the
> fix for the race?
Yes, the relevant commit is 3935baa9c9e6 ("hugepage: serialize hugepage 
allocation and instantiation"). This commit introduced the 
hugetlb_fault_mutex_table in mm/hugetlb.c which serializes hugepage 
allocation and instantiation to prevent spurious OOMs when two CPUs race 
to instantiate the same last available hugepage. The kernel comment at 
the lock declaration confirms it: "prevent spurious OOMs when the 
hugepage pool is fully utilized". Will add the linux-git tag in the next 
version
>
>> +#define _GNU_SOURCE
>> +#include <pthread.h>
>> +#include "tst_test.h"
>> +#include "tst_safe_pthread.h"
>> +#include "hugetlb.h"
>> +
>> +#define MNTPOINT "hugetlbfs/"
>> +
>> +static char *str_op;
>> +static int child1, child2, race_type;
>> +static int fd_sync = -1;
>> +static int fd_race = -1;
>> +static void *p_race = MAP_FAILED;
>> +static void *p_sync = MAP_FAILED;
>> +static size_t sync_mapping_size;
>> +
>> +struct racer_info {
>> +	void *p;
>> +	int cpu;
>> +	int status;
>> +};
>> +
>> +static int one_racer(void *p, int cpu)
>> +{
>> +	volatile int *pi = p;
>> +	cpu_set_t *cpuset;
>> +	size_t mask_size;
>> +	int err;
>> +
>> +	cpuset = CPU_ALLOC(cpu + 1);
>> +	if (!cpuset)
>> +		tst_brk(TBROK | TERRNO, "CPU_ALLOC() failed");
>> +
>> +	mask_size = CPU_ALLOC_SIZE(cpu + 1);
>> +
>> +	/* Split onto different CPUs to encourage the race */
>> +	CPU_ZERO_S(mask_size, cpuset);
>> +	CPU_SET_S(cpu, mask_size, cpuset);
>> +
>> +	/*
>> +	 * Use pid 0 so that sched_setaffinity() applies to the calling
>> +	 * thread rather than the thread-group leader.  getpid() returns
>> +	 * the same TGID for every pthread in the process, so passing it
>> +	 * would pin the main thread instead of the racer.
>> +	 */
>> +	err = sched_setaffinity(0, mask_size, cpuset);
>> +	CPU_FREE(cpuset);
>> +	if (err == -1)
>> +		tst_brk(TBROK | TERRNO, "sched_setaffinity() failed");
>> +
>> +	/* Wait for parent to signal both racers to start */
>> +	TST_CHECKPOINT_WAIT(0);
>> +
>> +	/* Fault in the hugepage - triggers the race */
>> +	*pi = 1;
> If this is the actual race, it would probably make sense to actually
> unmap/map and fault the page in a loop. We do have a tst_fuzzy_sync.h
> that has a machinery for synchronizing two processes to hit a race.
> Maybe it would make sense to use it.
Will address in the next version. Will add tst_fuzzy_sync.h and wrap the 
fault in a tst_fzsync_run_a/b() loop. After each iteration will unmap 
p_race and truncate fd_race to zero to return the hugepage to the pool, 
then remap for the next attempt.
>> +	return 0;
>> +}
>> +
>> +static void proc_racer(void *p, int cpu)
>> +{
>> +	exit(one_racer(p, cpu));
>> +}
>> +
>> +static void *thread_racer(void *info)
>> +{
>> +	struct racer_info *ri = info;
>> +
>> +	ri->status = one_racer(ri->p, ri->cpu);
>> +	return ri;
>> +}
>> +
>> +static void check_online_cpus(int online_cpus[], int nr_cpus_needed)
>> +{
>> +	cpu_set_t cpuset;
>> +	int total_cpus, cpu_idx;
>> +
>> +	CPU_ZERO(&cpuset);
>> +
>> +	total_cpus = get_nprocs_conf();
>> +
>> +	if (sched_getaffinity(0, sizeof(cpu_set_t), &cpuset) == -1)
>> +		tst_brk(TBROK | TERRNO, "sched_getaffinity() failed");
>> +
>> +	tst_res(TINFO, "Online CPUs needed: %d, available: %d",
>> +		nr_cpus_needed, CPU_COUNT(&cpuset));
>> +
>> +	if (CPU_COUNT(&cpuset) < nr_cpus_needed)
>> +		tst_brk(TCONF, "At least %d online CPUs are required",
>> +			nr_cpus_needed);
>> +
>> +	cpu_idx = 0;
>> +	for (int i = 0; i < total_cpus && cpu_idx < nr_cpus_needed; i++) {
>> +		if (CPU_ISSET(i, &cpuset))
>> +			online_cpus[cpu_idx++] = i;
>> +	}
>> +
>> +	if (cpu_idx < nr_cpus_needed)
>> +		tst_brk(TBROK, "Unable to find enough online CPUs");
>> +}
>> +
>> +static void run_race(int rtype)
>> +{
>> +	void *tret1, *tret2;
>> +	int status1 = 0, status2 = 0;
>> +	int online_cpus[2];
>> +	long hpage_size;
>> +	pthread_t thread1, thread2;
>> +
>> +	check_online_cpus(online_cpus, 2);
>> +
>> +	hpage_size = tst_get_hugepage_size();
>> +
>> +	/* Get a new file for the final page */
>> +	fd_race = tst_creat_unlinked(MNTPOINT, 0, 0600);
>> +	tst_res(TINFO, "Mapping final page..");
>> +
>> +	p_race = SAFE_MMAP(NULL, hpage_size, PROT_READ | PROT_WRITE,
>> +			   rtype, fd_race, 0);
>> +
>> +	if (rtype == MAP_SHARED) {
>> +		child1 = SAFE_FORK();
>> +		if (child1 == 0)
>> +			proc_racer(p_race, online_cpus[0]);
>> +
>> +		child2 = SAFE_FORK();
>> +		if (child2 == 0)
>> +			proc_racer(p_race, online_cpus[1]);
>> +
>> +		/* Wake both children to start the race simultaneously */
>> +		TST_CHECKPOINT_WAKE2(0, 2);
>> +
>> +		SAFE_WAITPID(child1, &status1, 0);
>> +		child1 = 0;
>> +		tst_res(TINFO, "Child 1 status: %x", status1);
>> +
>> +		SAFE_WAITPID(child2, &status2, 0);
>> +		child2 = 0;
>> +		tst_res(TINFO, "Child 2 status: %x", status2);
>> +
>> +		if (WIFSIGNALED(status1))
>> +			tst_res(TFAIL, "Child 1 killed by signal %s",
>> +				strsignal(WTERMSIG(status1)));
>> +		if (WIFSIGNALED(status2))
>> +			tst_res(TFAIL, "Child 2 killed by signal %s",
>> +				strsignal(WTERMSIG(status2)));
>> +	} else {
>> +		struct racer_info ri1 = {
>> +			.p = p_race,
>> +			.cpu = online_cpus[0],
>> +			.status = -1,
>> +		};
>> +		struct racer_info ri2 = {
>> +			.p = p_race,
>> +			.cpu = online_cpus[1],
>> +			.status = -1,
>> +		};
>> +
>> +		SAFE_PTHREAD_CREATE(&thread1, NULL, thread_racer, &ri1);
>> +		SAFE_PTHREAD_CREATE(&thread2, NULL, thread_racer, &ri2);
>> +
>> +		/* Wake both threads to start the race simultaneously */
>> +		TST_CHECKPOINT_WAKE2(0, 2);
>> +
>> +		SAFE_PTHREAD_JOIN(thread1, &tret1);
>> +		if (tret1 != &ri1)
>> +			tst_res(TFAIL, "Thread 1 returned %p not %p, killed?",
>> +				tret1, &ri1);
>> +
>> +		SAFE_PTHREAD_JOIN(thread2, &tret2);
>> +		if (tret2 != &ri2)
>> +			tst_res(TFAIL, "Thread 2 returned %p not %p, killed?",
>> +				tret2, &ri2);
>> +
>> +		status1 = ri1.status;
>> +		status2 = ri2.status;
> Here the ri1.status and ri2.status is completely bogus, since that
> either stays initialize to -1 or is set to 0 by clean exit of the
> functions. Since the description says that the bug triggers OOM all
> threads of the process would be killed if we reproduce the bug and we
> will never get to this place anyways.
>
> I suppose that you need to actually fork and then run the two threads in
> the forked process in order to isolate it from the main test process.
Will fix in the next version. Will remove struct racer_info and the 
bogus status checks. For the MAP_PRIVATE path will fork a child first 
and run both racing threads inside it, so an OOM kill only affects the 
child. The parent will detect failure via WIFSIGNALED().
>
>
>
> Also the two different test modes does not have nearly any code in
> common, so these two should be in two different functions.
Will fix in the next version. Will split into two separate functions 
run_shared_race() and run_private_race() and remove the combined 
run_race(int rtype) with the if/else block
>> +	}
>> +
>> +	if (status1 != 0)
>> +		tst_res(TFAIL, "Racer 1 terminated with code %d", status1);
>> +
>> +	if (status2 != 0)
>> +		tst_res(TFAIL, "Racer 2 terminated with code %d", status2);
>> +
>> +	if (status1 == 0 && status2 == 0)
>> +		tst_res(TPASS, "Test completed successfully");
>> +
>> +	SAFE_MUNMAP(p_race, hpage_size);
>> +	p_race = MAP_FAILED;
>> +
>> +	SAFE_CLOSE(fd_race);
>> +	fd_race = -1;
>> +}
>> +
>> +static void run_test(void)
>> +{
>> +	unsigned long totpages;
>> +	long hpage_size;
>> +
>> +	totpages = SAFE_READ_MEMINFO(MEMINFO_HPAGE_FREE);
>> +	if (totpages < 2)
>> +		tst_brk(TCONF, "Not enough free hugepages, need at least 2");
> This is done by the .hugepages = {2, TST_NEEDS} in the tst_test
> structure.
Will keep the .hugepages = {2, TST_NEEDS} for the initial reservation 
and remove the manual check from run_test() in the next version
>> +	hpage_size = tst_get_hugepage_size();
>> +
>> +	tst_res(TINFO, "Instantiating..");
>> +
>> +	fd_sync = tst_creat_unlinked(MNTPOINT, 0, 0600);
>> +
>> +	tst_res(TINFO, "Mapping %lu/%lu pages..", totpages - 1, totpages);
>> +	sync_mapping_size = (totpages - 1) * hpage_size;
>> +	p_sync = SAFE_MMAP(NULL, sync_mapping_size,
>> +			   PROT_READ | PROT_WRITE, MAP_SHARED, fd_sync, 0);
>> +
>> +	/*
>> +	 * Fault in every sync page to consume them from the hugepage pool.
>> +	 * Without touching each page, mmap() does not allocate hugepages
>> +	 * (no MAP_POPULATE), so all free hugepages remain available to the
>> +	 * racers and the allocation race is never exercised.
>> +	 */
>> +	for (unsigned long i = 0; i < totpages - 1; i++) {
>> +		volatile char *cp = (volatile char *)p_sync + i * hpage_size;
>> +
>> +		*cp = 0;
>> +	}
>> +
>> +	run_race(race_type);
>> +
>> +	SAFE_MUNMAP(p_sync, sync_mapping_size);
>> +	p_sync = MAP_FAILED;
>> +
>> +	SAFE_CLOSE(fd_sync);
>> +	fd_sync = -1;
> The fd is set to -1 by the SAFE_CLOSE()
>> +}
>> +
>> +static void setup(void)
>> +{
>> +	if (str_op) {
>> +		if (strcmp(str_op, "shared") == 0)
>> +			race_type = MAP_SHARED;
>> +		else if (strcmp(str_op, "private") == 0)
>> +			race_type = MAP_PRIVATE;
>> +		else
>> +			tst_brk(TBROK,
>> +				"Invalid parameter: use -m <private|shared>");
>> +	} else {
>> +		/* Default to shared if no option is passed */
>> +		race_type = MAP_SHARED;
>> +	}
>> +}
>> +
>> +static void cleanup(void)
>> +{
>> +	if (p_race != MAP_FAILED)
>> +		SAFE_MUNMAP(p_race, tst_get_hugepage_size());
>> +
>> +	if (fd_race >= 0)
> fd_race != -1
Will fix in the next version. Will remove the redundant fd_sync = -1 and 
fd_race = -1 assignments after SAFE_CLOSE().
>> +		SAFE_CLOSE(fd_race);
>> +
>> +	/*
>> +	 * Use the saved sync_mapping_size rather than re-reading
>> +	 * MEMINFO_HPAGE_FREE: the current free count differs from the
>> +	 * mapping length and could cause munmap() to remove an adjacent
>> +	 * mapping or leave part of p_sync mapped.
>> +	 */
>> +	if (p_sync != MAP_FAILED)
>> +		SAFE_MUNMAP(p_sync, sync_mapping_size);
>> +
>> +	if (fd_sync >= 0)
>> +		SAFE_CLOSE(fd_sync);
>> +
>> +	if (child1 > 0) {
>> +		if (kill(child1, 0) == 0)
>> +			SAFE_KILL(child1, SIGKILL);
>> +	}
>> +
>> +	if (child2 > 0) {
>> +		if (kill(child2, 0) == 0)
>> +			SAFE_KILL(child2, SIGKILL);
>> +	}
>> +}
>> +
>> +static struct tst_test test = {
>> +	.options = (struct tst_option[]) {
>> +		{"m:", &str_op, "Type of mmap() mapping <private|shared>"},
>> +		{}
>> +	},
>> +	.needs_root = 1,
>> +	.mntpoint = MNTPOINT,
>> +	.needs_hugetlbfs = 1,
>> +	.needs_tmpdir = 1,
>> +	.setup = setup,
>> +	.cleanup = cleanup,
>> +	.test_all = run_test,
>> +	.hugepages = {2, TST_NEEDS},
>> +	.forks_child = 1,
>> +	.needs_checkpoints = 1,
>> +	.min_cpus = 2,
>> +};
>> -- 
>> 2.52.0
>>
Thank you Cyril for the review comments.

Regards,
Samir

-- 
Mailing list info: https://lists.linux.it/listinfo/ltp