[LTP] [PATCH v3] userfaultfd: Add test using UFFDIO_POISON

[LTP] [PATCH v3] userfaultfd: Add test using UFFDIO_POISON

[Ricardo Branco]

Signed-off-by: Ricardo Branco <rbranco@suse.de>
---
 configure.ac                                  |   1 +
 include/lapi/userfaultfd.h                    |  13 ++
 .../kernel/syscalls/userfaultfd/.gitignore    |   1 +
 .../kernel/syscalls/userfaultfd/Makefile      |   1 +
 .../syscalls/userfaultfd/userfaultfd06.c      | 134 ++++++++++++++++++
 5 files changed, 150 insertions(+)
 create mode 100644 testcases/kernel/syscalls/userfaultfd/userfaultfd06.c

diff --git a/configure.ac b/configure.ac
index 7fa614dcb..94bcbcc98 100644
--- a/configure.ac
+++ b/configure.ac
@@ -278,6 +278,7 @@ AC_CHECK_TYPES([struct sockaddr_vm],,,[
 ])
 
 AC_CHECK_TYPES([struct uffdio_move],,,[#include <linux/userfaultfd.h>])
+AC_CHECK_TYPES([struct uffdio_poison],,,[#include <linux/userfaultfd.h>])
 AC_CHECK_TYPES([struct uffdio_writeprotect],,,[#include <linux/userfaultfd.h>])
 
 # Tools knobs
diff --git a/include/lapi/userfaultfd.h b/include/lapi/userfaultfd.h
index 0c9e34c84..aab3890b7 100644
--- a/include/lapi/userfaultfd.h
+++ b/include/lapi/userfaultfd.h
@@ -233,6 +233,19 @@ struct uffdio_writeprotect {
 };
 #endif	/* HAVE_STRUCT_UFFDIO_WRITEPROTECT */
 
+#ifndef HAVE_STRUCT_UFFDIO_POISON
+#define UFFD_FEATURE_POISON			(1<<14)
+#define _UFFDIO_POISON				(0x08)
+#define UFFDIO_POISON		_IOWR(UFFDIO, _UFFDIO_POISON, \
+				      struct uffdio_poison)
+struct uffdio_poison {
+        struct uffdio_range range;
+#define UFFDIO_POISON_MODE_DONTWAKE		((__u64)1<<0)
+        __u64 mode;
+        __s64 updated;
+};
+#endif	/* HAVE_STRUCT_UFFDIO_POISON */
+
 #define SAFE_USERFAULTFD(flags, retry) \
 	safe_userfaultfd(__FILE__, __LINE__, (flags), (retry))
 
diff --git a/testcases/kernel/syscalls/userfaultfd/.gitignore b/testcases/kernel/syscalls/userfaultfd/.gitignore
index fb2ae243b..bc32fdf3b 100644
--- a/testcases/kernel/syscalls/userfaultfd/.gitignore
+++ b/testcases/kernel/syscalls/userfaultfd/.gitignore
@@ -3,3 +3,4 @@
 /userfaultfd03
 /userfaultfd04
 /userfaultfd05
+/userfaultfd06
diff --git a/testcases/kernel/syscalls/userfaultfd/Makefile b/testcases/kernel/syscalls/userfaultfd/Makefile
index 96650a65a..3252e47df 100644
--- a/testcases/kernel/syscalls/userfaultfd/Makefile
+++ b/testcases/kernel/syscalls/userfaultfd/Makefile
@@ -16,3 +16,4 @@ userfaultfd02: CFLAGS += -pthread
 userfaultfd03: CFLAGS += -pthread
 userfaultfd04: CFLAGS += -pthread
 userfaultfd05: CFLAGS += -pthread
+userfaultfd06: CFLAGS += -pthread
diff --git a/testcases/kernel/syscalls/userfaultfd/userfaultfd06.c b/testcases/kernel/syscalls/userfaultfd/userfaultfd06.c
new file mode 100644
index 000000000..c4546acce
--- /dev/null
+++ b/testcases/kernel/syscalls/userfaultfd/userfaultfd06.c
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2026 SUSE LLC
+ * Author: Ricardo Branco <rbranco@suse.com>
+ */
+
+/*\
+ * Force a pagefault event and handle it using :manpage:`userfaultfd(2)`
+ * from a different thread testing UFFDIO_POISON.
+ */
+
+#include "config.h"
+#include <poll.h>
+#include <setjmp.h>
+#include <signal.h>
+#include <unistd.h>
+#include "tst_test.h"
+#include "tst_safe_macros.h"
+#include "tst_safe_pthread.h"
+#include "lapi/userfaultfd.h"
+
+static int page_size;
+static char *page;
+static int uffd;
+static volatile int poison_fault_seen;
+static volatile int sigbus_seen;
+static sigjmp_buf jmpbuf;
+
+static void sigbus_handler(int sig)
+{
+	if (sig == SIGBUS) {
+		sigbus_seen = 1;
+		siglongjmp(jmpbuf, 1);
+	}
+}
+
+static void set_pages(void)
+{
+	page_size = sysconf(_SC_PAGE_SIZE);
+	page = SAFE_MMAP(NULL, page_size, PROT_READ | PROT_WRITE,
+			MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+}
+
+static void reset_pages(void)
+{
+	if (page) {
+		SAFE_MUNMAP(page, page_size);
+		page = NULL;
+	}
+}
+
+static void *handle_thread(void)
+{
+	static struct uffd_msg msg;
+	struct uffdio_poison uffdio_poison = {};
+	struct pollfd pollfd;
+	int nready;
+
+	pollfd.fd = uffd;
+	pollfd.events = POLLIN;
+	nready = poll(&pollfd, 1, -1);
+	if (nready == -1)
+		tst_brk(TBROK | TERRNO, "Error on poll");
+
+	SAFE_READ(1, uffd, &msg, sizeof(msg));
+
+	if (msg.event != UFFD_EVENT_PAGEFAULT)
+		tst_brk(TFAIL, "Received unexpected UFFD_EVENT %d", msg.event);
+
+	poison_fault_seen = 1;
+
+	/* Poison the page that triggered the fault */
+	uffdio_poison.range.start = msg.arg.pagefault.address & ~(page_size - 1);
+	uffdio_poison.range.len = page_size;
+
+	SAFE_IOCTL(uffd, UFFDIO_POISON, &uffdio_poison);
+
+	close(uffd);
+	return NULL;
+}
+
+static void run(void)
+{
+	pthread_t thr;
+	struct uffdio_api uffdio_api = {};
+	struct uffdio_register uffdio_register;
+	struct sigaction sa = {};
+	volatile char dummy;
+
+	sa.sa_handler = sigbus_handler;
+	sigemptyset(&sa.sa_mask);
+	SAFE_SIGACTION(SIGBUS, &sa, NULL);
+
+	set_pages();
+
+	uffd = SAFE_USERFAULTFD(O_CLOEXEC | O_NONBLOCK, false);
+
+	uffdio_api.api = UFFD_API;
+	uffdio_api.features = UFFD_FEATURE_POISON;
+
+	SAFE_IOCTL(uffd, UFFDIO_API, &uffdio_api);
+
+	uffdio_register.range.start = (unsigned long) page;
+	uffdio_register.range.len = page_size;
+	uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
+
+	SAFE_IOCTL(uffd, UFFDIO_REGISTER, &uffdio_register);
+
+	SAFE_PTHREAD_CREATE(&thr, NULL, (void *) handle_thread, NULL);
+
+	/* Try to read from the page: should trigger fault, get poisoned, then SIGBUS */
+	if (sigsetjmp(jmpbuf, 1) == 0) {
+		dummy = page[0];
+		(void)dummy;
+	}
+
+	SAFE_PTHREAD_JOIN(thr, NULL);
+	reset_pages();
+
+	if (poison_fault_seen && sigbus_seen) {
+		tst_res(TPASS, "POISON successfully triggered SIGBUS");
+	} else if (poison_fault_seen && !sigbus_seen) {
+		tst_res(TFAIL, "POISON fault seen but no SIGBUS received");
+	} else if (!poison_fault_seen && sigbus_seen) {
+		tst_res(TFAIL, "SIGBUS received but no poison fault seen");
+	} else {
+		tst_res(TFAIL, "No poison fault or SIGBUS observed");
+	}
+}
+
+static struct tst_test test = {
+	.test_all = run,
+	.min_kver = "6.6",
+};
-- 
2.53.0


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Re: [LTP] [PATCH v3] userfaultfd: Add test using UFFDIO_POISON

[Andrea Cervesato via ltp]

Hi!

On Wed Feb 18, 2026 at 2:50 PM CET, Ricardo Branco wrote:
> Signed-off-by: Ricardo Branco <rbranco@suse.de>
> ---
>  configure.ac                                  |   1 +
>  include/lapi/userfaultfd.h                    |  13 ++
>  .../kernel/syscalls/userfaultfd/.gitignore    |   1 +
>  .../kernel/syscalls/userfaultfd/Makefile      |   1 +
>  .../syscalls/userfaultfd/userfaultfd06.c      | 134 ++++++++++++++++++
>  5 files changed, 150 insertions(+)
>  create mode 100644 testcases/kernel/syscalls/userfaultfd/userfaultfd06.c
>
> diff --git a/configure.ac b/configure.ac
> index 7fa614dcb..94bcbcc98 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -278,6 +278,7 @@ AC_CHECK_TYPES([struct sockaddr_vm],,,[
>  ])
>  
>  AC_CHECK_TYPES([struct uffdio_move],,,[#include <linux/userfaultfd.h>])
> +AC_CHECK_TYPES([struct uffdio_poison],,,[#include <linux/userfaultfd.h>])
>  AC_CHECK_TYPES([struct uffdio_writeprotect],,,[#include <linux/userfaultfd.h>])
>  
>  # Tools knobs
> diff --git a/include/lapi/userfaultfd.h b/include/lapi/userfaultfd.h
> index 0c9e34c84..aab3890b7 100644
> --- a/include/lapi/userfaultfd.h
> +++ b/include/lapi/userfaultfd.h
> @@ -233,6 +233,19 @@ struct uffdio_writeprotect {
>  };
>  #endif	/* HAVE_STRUCT_UFFDIO_WRITEPROTECT */
>  
> +#ifndef HAVE_STRUCT_UFFDIO_POISON
> +#define UFFD_FEATURE_POISON			(1<<14)
> +#define _UFFDIO_POISON				(0x08)
> +#define UFFDIO_POISON		_IOWR(UFFDIO, _UFFDIO_POISON, \
> +				      struct uffdio_poison)
> +struct uffdio_poison {
> +        struct uffdio_range range;
> +#define UFFDIO_POISON_MODE_DONTWAKE		((__u64)1<<0)
> +        __u64 mode;
> +        __s64 updated;
> +};
> +#endif	/* HAVE_STRUCT_UFFDIO_POISON */
> +
>  #define SAFE_USERFAULTFD(flags, retry) \
>  	safe_userfaultfd(__FILE__, __LINE__, (flags), (retry))
>  
> diff --git a/testcases/kernel/syscalls/userfaultfd/.gitignore b/testcases/kernel/syscalls/userfaultfd/.gitignore
> index fb2ae243b..bc32fdf3b 100644
> --- a/testcases/kernel/syscalls/userfaultfd/.gitignore
> +++ b/testcases/kernel/syscalls/userfaultfd/.gitignore
> @@ -3,3 +3,4 @@
>  /userfaultfd03
>  /userfaultfd04
>  /userfaultfd05
> +/userfaultfd06
> diff --git a/testcases/kernel/syscalls/userfaultfd/Makefile b/testcases/kernel/syscalls/userfaultfd/Makefile
> index 96650a65a..3252e47df 100644
> --- a/testcases/kernel/syscalls/userfaultfd/Makefile
> +++ b/testcases/kernel/syscalls/userfaultfd/Makefile
> @@ -16,3 +16,4 @@ userfaultfd02: CFLAGS += -pthread
>  userfaultfd03: CFLAGS += -pthread
>  userfaultfd04: CFLAGS += -pthread
>  userfaultfd05: CFLAGS += -pthread
> +userfaultfd06: CFLAGS += -pthread
> diff --git a/testcases/kernel/syscalls/userfaultfd/userfaultfd06.c b/testcases/kernel/syscalls/userfaultfd/userfaultfd06.c
> new file mode 100644
> index 000000000..c4546acce
> --- /dev/null
> +++ b/testcases/kernel/syscalls/userfaultfd/userfaultfd06.c
> @@ -0,0 +1,134 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (c) 2026 SUSE LLC
> + * Author: Ricardo Branco <rbranco@suse.com>
> + */
> +
> +/*\
> + * Force a pagefault event and handle it using :manpage:`userfaultfd(2)`
> + * from a different thread testing UFFDIO_POISON.
> + */
> +
> +#include "config.h"
> +#include <poll.h>
> +#include <setjmp.h>
> +#include <signal.h>
> +#include <unistd.h>
> +#include "tst_test.h"
> +#include "tst_safe_macros.h"
> +#include "tst_safe_pthread.h"
> +#include "lapi/userfaultfd.h"
> +
> +static int page_size;
> +static char *page;
> +static int uffd;
> +static volatile int poison_fault_seen;
> +static volatile int sigbus_seen;
> +static sigjmp_buf jmpbuf;
> +
> +static void sigbus_handler(int sig)
> +{
> +	if (sig == SIGBUS) {
> +		sigbus_seen = 1;
> +		siglongjmp(jmpbuf, 1);
> +	}
> +}
> +
> +static void set_pages(void)
> +{
> +	page_size = sysconf(_SC_PAGE_SIZE);
> +	page = SAFE_MMAP(NULL, page_size, PROT_READ | PROT_WRITE,
> +			MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> +}
> +
> +static void reset_pages(void)
> +{
> +	if (page) {
> +		SAFE_MUNMAP(page, page_size);
> +		page = NULL;
> +	}
> +}
> +
> +static void *handle_thread(void)
> +{
> +	static struct uffd_msg msg;
> +	struct uffdio_poison uffdio_poison = {};
> +	struct pollfd pollfd;
> +	int nready;
> +
> +	pollfd.fd = uffd;
> +	pollfd.events = POLLIN;
> +	nready = poll(&pollfd, 1, -1);
> +	if (nready == -1)
> +		tst_brk(TBROK | TERRNO, "Error on poll");
> +
> +	SAFE_READ(1, uffd, &msg, sizeof(msg));
> +
> +	if (msg.event != UFFD_EVENT_PAGEFAULT)
> +		tst_brk(TFAIL, "Received unexpected UFFD_EVENT %d", msg.event);
> +
> +	poison_fault_seen = 1;
> +
> +	/* Poison the page that triggered the fault */
> +	uffdio_poison.range.start = msg.arg.pagefault.address & ~(page_size - 1);
> +	uffdio_poison.range.len = page_size;
> +
> +	SAFE_IOCTL(uffd, UFFDIO_POISON, &uffdio_poison);
> +
> +	close(uffd);
> +	return NULL;
> +}
> +
> +static void run(void)
> +{
> +	pthread_t thr;
> +	struct uffdio_api uffdio_api = {};
> +	struct uffdio_register uffdio_register;
> +	struct sigaction sa = {};
> +	volatile char dummy;
> +
> +	sa.sa_handler = sigbus_handler;
> +	sigemptyset(&sa.sa_mask);
> +	SAFE_SIGACTION(SIGBUS, &sa, NULL);
> +
> +	set_pages();
> +
> +	uffd = SAFE_USERFAULTFD(O_CLOEXEC | O_NONBLOCK, false);
> +
> +	uffdio_api.api = UFFD_API;
> +	uffdio_api.features = UFFD_FEATURE_POISON;
> +
> +	SAFE_IOCTL(uffd, UFFDIO_API, &uffdio_api);
> +
> +	uffdio_register.range.start = (unsigned long) page;
> +	uffdio_register.range.len = page_size;
> +	uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
> +
> +	SAFE_IOCTL(uffd, UFFDIO_REGISTER, &uffdio_register);
> +
> +	SAFE_PTHREAD_CREATE(&thr, NULL, (void *) handle_thread, NULL);
> +
> +	/* Try to read from the page: should trigger fault, get poisoned, then SIGBUS */
> +	if (sigsetjmp(jmpbuf, 1) == 0) {
> +		dummy = page[0];
> +		(void)dummy;
> +	}
> +
> +	SAFE_PTHREAD_JOIN(thr, NULL);
> +	reset_pages();

This should also go into a cleanup(), otherwise if other syscalls will
fail (ioctl for instance), memory will be lost.

> +
> +	if (poison_fault_seen && sigbus_seen) {
> +		tst_res(TPASS, "POISON successfully triggered SIGBUS");
> +	} else if (poison_fault_seen && !sigbus_seen) {
> +		tst_res(TFAIL, "POISON fault seen but no SIGBUS received");
> +	} else if (!poison_fault_seen && sigbus_seen) {
> +		tst_res(TFAIL, "SIGBUS received but no poison fault seen");
> +	} else {
> +		tst_res(TFAIL, "No poison fault or SIGBUS observed");
> +	}
> +}
> +
> +static struct tst_test test = {
> +	.test_all = run,
> +	.min_kver = "6.6",

This is not needed, we should use UFFDIO_API instead, in order to verify
that UFFD_FEATURE_POISON is present and eventually TCONF.


Also, if I run checkpatch.pl on the code I get:

WARNING: Use of volatile is usually wrong: see Documentation/process/volatile-considered-harmful.rst
#25: FILE: userfaultfd06.c:25:
+static volatile int poison_fault_seen;

WARNING: Use of volatile is usually wrong: see Documentation/process/volatile-considered-harmful.rst
#26: FILE: userfaultfd06.c:26:
+static volatile int sigbus_seen;

WARNING: Use of volatile is usually wrong: see Documentation/process/volatile-considered-harmful.rst
#88: FILE: userfaultfd06.c:88:
+       volatile char dummy;

WARNING: braces {} are not necessary for any arm of this statement
#120: FILE: userfaultfd06.c:120:
+       if (poison_fault_seen && sigbus_seen) {
[...]
+       } else if (poison_fault_seen && !sigbus_seen) {
[...]
+       } else if (!poison_fault_seen && sigbus_seen) {
[...]
+       } else {
[...]

total: 0 errors, 4 warnings, 134 lines checked

NOTE: For some of the reported defects, checkpatch may be able to
      mechanically convert to the typical style using --fix or --fix-inplace.

userfaultfd06.c has style problems, please review.

NOTE: If any of the errors are false positives, please report
      them to the maintainer, see CHECKPATCH in MAINTAINERS.

If you have `b4`, please run `b4 prep --check` before sending the patch.

-- 
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com


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

Re: [LTP] [PATCH v3] userfaultfd: Add test using UFFDIO_POISON

[Ricardo Branco]

On 2/19/26 10:54 AM, Andrea Cervesato wrote:
>> +	SAFE_PTHREAD_JOIN(thr, NULL);
>> +	reset_pages();
> This should also go into a cleanup(), otherwise if other syscalls will
> fail (ioctl for instance), memory will be lost.
Will fix this in userfaultfd06.c and then submit another to fix it in 
the rest.

> Also, if I run checkpatch.pl on the code I get:
>
> WARNING: Use of volatile is usually wrong: see Documentation/process/volatile-considered-harmful.rst
> #25: FILE: userfaultfd06.c:25:
> +static volatile int poison_fault_seen;
>
> WARNING: Use of volatile is usually wrong: see Documentation/process/volatile-considered-harmful.rst
> #26: FILE: userfaultfd06.c:26:
> +static volatile int sigbus_seen;
>
> WARNING: Use of volatile is usually wrong: see Documentation/process/volatile-considered-harmful.rst
> #88: FILE: userfaultfd06.c:88:
> +       volatile char dummy;

I've seen volatile being used in tests. There are legitimate uses for 
this, in signal handlers.

> If you have `b4`, please run `b4 prep --check` before sending the patch.
I'm getting:
CRITICAL: This is not a prep-managed branch.

Best,
R.


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Re: [LTP] [PATCH v3] userfaultfd: Add test using UFFDIO_POISON

[Cyril Hrubis]

Hi!
> > +	SAFE_PTHREAD_JOIN(thr, NULL);
> > +	reset_pages();
> 
> This should also go into a cleanup(), otherwise if other syscalls will
> fail (ioctl for instance), memory will be lost.

Technically all memory is released when last reference to it is removed,
which happens on process exit. So no mmaped() memory is not going to
leak.

> > +	if (poison_fault_seen && sigbus_seen) {
> > +		tst_res(TPASS, "POISON successfully triggered SIGBUS");
> > +	} else if (poison_fault_seen && !sigbus_seen) {
> > +		tst_res(TFAIL, "POISON fault seen but no SIGBUS received");
> > +	} else if (!poison_fault_seen && sigbus_seen) {
> > +		tst_res(TFAIL, "SIGBUS received but no poison fault seen");
> > +	} else {
> > +		tst_res(TFAIL, "No poison fault or SIGBUS observed");
> > +	}
> > +}
> > +
> > +static struct tst_test test = {
> > +	.test_all = run,
> > +	.min_kver = "6.6",
> 
> This is not needed, we should use UFFDIO_API instead, in order to verify
> that UFFD_FEATURE_POISON is present and eventually TCONF.
> 
> 
> Also, if I run checkpatch.pl on the code I get:
> 
> WARNING: Use of volatile is usually wrong: see Documentation/process/volatile-considered-harmful.rst
> #25: FILE: userfaultfd06.c:25:
> +static volatile int poison_fault_seen;

For variables changed from a different thread atomic operation are
better than volatile, i.e. tst_atomic_load() and tst_atomic_store().

> WARNING: Use of volatile is usually wrong: see Documentation/process/volatile-considered-harmful.rst
> #26: FILE: userfaultfd06.c:26:
> +static volatile int sigbus_seen;

This one is wrong, volatile is correct for variables changed for syscall
handlers.

> WARNING: Use of volatile is usually wrong: see Documentation/process/volatile-considered-harmful.rst
> #88: FILE: userfaultfd06.c:88:
> +       volatile char dummy;

I do not think that volatile is needed here.

> WARNING: braces {} are not necessary for any arm of this statement
> #120: FILE: userfaultfd06.c:120:
> +       if (poison_fault_seen && sigbus_seen) {
> [...]
> +       } else if (poison_fault_seen && !sigbus_seen) {
> [...]
> +       } else if (!poison_fault_seen && sigbus_seen) {
> [...]
> +       } else {
> [...]
> 
> total: 0 errors, 4 warnings, 134 lines checked
> 
> NOTE: For some of the reported defects, checkpatch may be able to
>       mechanically convert to the typical style using --fix or --fix-inplace.
> 
> userfaultfd06.c has style problems, please review.
> 
> NOTE: If any of the errors are false positives, please report
>       them to the maintainer, see CHECKPATCH in MAINTAINERS.
> 
> If you have `b4`, please run `b4 prep --check` before sending the patch.
> 
> -- 
> Andrea Cervesato
> SUSE QE Automation Engineer Linux
> andrea.cervesato@suse.com
> 
> 
> -- 
> Mailing list info: https://lists.linux.it/listinfo/ltp

-- 
Cyril Hrubis
chrubis@suse.cz

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

Re: [LTP] [PATCH v3] userfaultfd: Add test using UFFDIO_POISON

[Andrea Cervesato via ltp]

>
> This one is wrong, volatile is correct for variables changed for syscall
> handlers.

If this is wrong, we should verify checkpatch.pl configuration.

-- 
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com


-- 
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Re: [LTP] [PATCH v3] userfaultfd: Add test using UFFDIO_POISON

[Andrea Cervesato via ltp]

> CRITICAL: This is not a prep-managed branch.
>

That's because you didn't start to develop this feature in a `b4`
branch. The tool requires `b4 prep -n <my starting branch>` command
before starting the implementation.

But this (of course) requires `b4` knowledge :-) I'm planning to create
a small section inside documentation for `b4` usage.

Kind regards,
-- 
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com


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Re: [LTP] [PATCH v3] userfaultfd: Add test using UFFDIO_POISON

[Andrea Cervesato via ltp]

> Technically all memory is released when last reference to it is removed,
> which happens on process exit. So no mmaped() memory is not going to
> leak.
>

Yes, still, we should make sure that it's released at the end of the
test. Same for for malloc() memory allocation.

-- 
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com


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Re: [LTP] [PATCH v3] userfaultfd: Add test using UFFDIO_POISON

[Cyril Hrubis]

Hi!
> > This one is wrong, volatile is correct for variables changed for syscall
> > handlers.
> 
> If this is wrong, we should verify checkpatch.pl configuration.

It's only correct in very special situations such as signal handlers. I
do not think that we can catch that with checkpatch.

-- 
Cyril Hrubis
chrubis@suse.cz

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Re: [LTP] [PATCH v3] userfaultfd: Add test using UFFDIO_POISON

[Ricardo Branco]

On 2/19/26 12:24 PM, Cyril Hrubis wrote:
>> WARNING: Use of volatile is usually wrong: see Documentation/process/volatile-considered-harmful.rst
>> #88: FILE: userfaultfd06.c:88:
>> +       volatile char dummy;
> I do not think that volatile is needed here.

This is needed.  Without it, the test hangs.

Best,
R

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Re: [LTP] [PATCH v3] userfaultfd: Add test using UFFDIO_POISON

[Cyril Hrubis]

Hi!
> >> WARNING: Use of volatile is usually wrong: see Documentation/process/volatile-considered-harmful.rst
> >> #88: FILE: userfaultfd06.c:88:
> >> +       volatile char dummy;
> > I do not think that volatile is needed here.
> 
> This is needed.  Without it, the test hangs.

I suppose that the compiler optimizes out the read because we are not
using the value. We do have a maybe a bit more descriptive macro for
these cases called LTP_VAR_USED().

-- 
Cyril Hrubis
chrubis@suse.cz

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