linux-kernel - [PATCH v2] select: store end_time as timespec64 in restart block

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Message-Id: <20251223-restart-block-expiration-v2-1-8e33e5df7359@linutronix.de>
Date: Tue, 23 Dec 2025 08:00:39 +0100
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Alexander Viro <viro@...iv.linux.org.uk>, 
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Subject: [PATCH v2] select: store end_time as timespec64 in restart block

Storing the end time seconds as 'unsigned long' can lead to truncation
on 32-bit architectures if assigned from the 64-bit timespec64::tv_sec.
As the select() core uses timespec64 consistently, also use that in the
restart block.

This also allows the simplification of the accessors.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Reviewed-by: Jan Kara <jack@...e.cz>
---
Changes in v2:
- Drop already applied patches, and trim recipients accordingly
- Pick up review tags
- Link to v1: https://lore.kernel.org/r/20251110-restart-block-expiration-v1-0-5d39cc93df4f@linutronix.de
---
 fs/select.c                   | 12 ++++--------
 include/linux/restart_block.h |  4 ++--
 2 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/fs/select.c b/fs/select.c
index 65019b8ba3f7..78a1508c84d3 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -1038,14 +1038,11 @@ static long do_restart_poll(struct restart_block *restart_block)
 {
 	struct pollfd __user *ufds = restart_block->poll.ufds;
 	int nfds = restart_block->poll.nfds;
-	struct timespec64 *to = NULL, end_time;
+	struct timespec64 *to = NULL;
 	int ret;
 
-	if (restart_block->poll.has_timeout) {
-		end_time.tv_sec = restart_block->poll.tv_sec;
-		end_time.tv_nsec = restart_block->poll.tv_nsec;
-		to = &end_time;
-	}
+	if (restart_block->poll.has_timeout)
+		to = &restart_block->poll.end_time;
 
 	ret = do_sys_poll(ufds, nfds, to);
 
@@ -1077,8 +1074,7 @@ SYSCALL_DEFINE3(poll, struct pollfd __user *, ufds, unsigned int, nfds,
 		restart_block->poll.nfds = nfds;
 
 		if (timeout_msecs >= 0) {
-			restart_block->poll.tv_sec = end_time.tv_sec;
-			restart_block->poll.tv_nsec = end_time.tv_nsec;
+			restart_block->poll.end_time = end_time;
 			restart_block->poll.has_timeout = 1;
 		} else
 			restart_block->poll.has_timeout = 0;
diff --git a/include/linux/restart_block.h b/include/linux/restart_block.h
index 67d2bf579942..9b262109726d 100644
--- a/include/linux/restart_block.h
+++ b/include/linux/restart_block.h
@@ -6,6 +6,7 @@
 #define __LINUX_RESTART_BLOCK_H
 
 #include <linux/compiler.h>
+#include <linux/time64.h>
 #include <linux/types.h>
 
 struct __kernel_timespec;
@@ -50,8 +51,7 @@ struct restart_block {
 			struct pollfd __user *ufds;
 			int nfds;
 			int has_timeout;
-			unsigned long tv_sec;
-			unsigned long tv_nsec;
+			struct timespec64 end_time;
 		} poll;
 	};
 };

---
base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
change-id: 20251107-restart-block-expiration-52915454d881

Best regards,
-- 
Thomas Weißschuh <thomas.weissschuh@...utronix.de>