linux-kernel - [tip: locking/urgent] futex: Fix hardcoded flags

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Message-ID: <169999900615.391.871692364626596753.tip-bot2@tip-bot2>
Date:   Tue, 14 Nov 2023 21:56:46 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Xi Ruoyao <xry111@...111.site>,
        Florian Weimer <fweimer@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: locking/urgent] futex: Fix hardcoded flags

The following commit has been merged into the locking/urgent branch of tip:

Commit-ID:     59f3daffefbf48206dbf310af5472d6d7d7161df
Gitweb:        https://git.kernel.org/tip/59f3daffefbf48206dbf310af5472d6d7d7161df
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Tue, 14 Nov 2023 21:36:13 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 14 Nov 2023 22:26:41 +01:00

futex: Fix hardcoded flags

Xi reported that commit 5694289ce183 ("futex: Flag conversion") broke
glibc's robust futex tests.

This was narrowed down to the change of FLAGS_SHARED from 0x01 to
0x10, at which point Florian noted that handle_futex_death() has a
hardcoded flags argument of 1.

Change this to: FLAGS_SIZE_32 | FLAGS_SHARED, matching how
futex_to_flags() unconditionally sets FLAGS_SIZE_32 for all legacy
futex ops.

Fixes: 5694289ce183 ("futex: Flag conversion")
Reported-by: Xi Ruoyao <xry111@...111.site>
Reported-by: Florian Weimer <fweimer@...hat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20231114201402.GA25315@noisy.programming.kicks-ass.net
---
 kernel/futex/core.c |  9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index 52695c5..dad981a 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -700,7 +700,8 @@ retry:
 	owner = uval & FUTEX_TID_MASK;
 
 	if (pending_op && !pi && !owner) {
-		futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
+		futex_wake(uaddr, FLAGS_SIZE_32 | FLAGS_SHARED, 1,
+			   FUTEX_BITSET_MATCH_ANY);
 		return 0;
 	}
 
@@ -752,8 +753,10 @@ retry:
 	 * Wake robust non-PI futexes here. The wakeup of
 	 * PI futexes happens in exit_pi_state():
 	 */
-	if (!pi && (uval & FUTEX_WAITERS))
-		futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
+	if (!pi && (uval & FUTEX_WAITERS)) {
+		futex_wake(uaddr, FLAGS_SIZE_32 | FLAGS_SHARED, 1,
+			   FUTEX_BITSET_MATCH_ANY);
+	}
 
 	return 0;
 }