[PATCH v3 5/8] pidfs: Use test_bit_acquire() for attr flag tests

[Jinjie Ruan <ruanjinjie@huawei.com>]

Replace test_bit() + smp_rmb() with test_bit_acquire() for
PIDFS_ATTR_BIT_EXIT and PIDFS_ATTR_BIT_COREDUMP tests in pidfd_info().

The acquire semantics ensure that if the flag is observed set, the
associated attr fields written before smp_wmb() + set_bit() are
also visible.

Writers keep smp_wmb() + set_bit() since no release bitop exists.

Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Assisted-by: DeepSeek:DeepSeek-V3
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
---
 fs/pidfs.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/fs/pidfs.c b/fs/pidfs.c
index a6a643f15d08..2cd0fab73180 100644
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -393,8 +393,7 @@ static long pidfd_info(struct file *file, unsigned int cmd, unsigned long arg)
 
 	attr = READ_ONCE(pid->attr);
 	if (mask & PIDFD_INFO_EXIT) {
-		if (test_bit(PIDFS_ATTR_BIT_EXIT, &attr->attr_mask)) {
-			smp_rmb();
+		if (test_bit_acquire(PIDFS_ATTR_BIT_EXIT, &attr->attr_mask)) {
 			kinfo.mask |= PIDFD_INFO_EXIT;
 #ifdef CONFIG_CGROUPS
 			kinfo.cgroupid = attr->cgroupid;
@@ -405,8 +404,7 @@ static long pidfd_info(struct file *file, unsigned int cmd, unsigned long arg)
 	}
 
 	if (mask & PIDFD_INFO_COREDUMP) {
-		if (test_bit(PIDFS_ATTR_BIT_COREDUMP, &attr->attr_mask)) {
-			smp_rmb();
+		if (test_bit_acquire(PIDFS_ATTR_BIT_COREDUMP, &attr->attr_mask)) {
 			kinfo.mask |= PIDFD_INFO_COREDUMP | PIDFD_INFO_COREDUMP_SIGNAL | PIDFD_INFO_COREDUMP_CODE;
 			kinfo.coredump_mask = attr->coredump_mask;
 			kinfo.coredump_signal = attr->coredump_signal;
-- 
2.34.1