git: df436036e82b - main - umtx: Don't sleep after casueword32 failure in do_sem2_wake

[Bojan Novković]

The branch main has been updated by bnovkov:

URL: 
https://cgit.FreeBSD.org/src/commit/?id=df436036e82b895a6233d803bc8bf14d2cfe90d7

commit df436036e82b895a6233d803bc8bf14d2cfe90d7
Author:     Bojan Novković <bnov...@freebsd.org>
AuthorDate: 2025-01-30 15:10:04 +0000
Commit:     Bojan Novković <bnov...@freebsd.org>
CommitDate: 2025-02-17 16:40:34 +0000

    umtx: Don't sleep after casueword32 failure in do_sem2_wake
    
    When a casueword32 operation fails, 'do_sem2_wake' will call
    'thread_check_susp' to avoid a potential livelock. However, it
    instructs 'thread_check_susp' to sleep while holding a previously busied
    umtxq key. This is explicitly discouraged by the comments in
    'thread_check_susp' which state that a thread shouldn't sleep if it
    owns a kernel resource. Fix this by passing 'false'
    to 'thread_check_susp'.
    
    Reviewed by:    kib
    PR:             282713
    Differential Revision:  https://reviews.freebsd.org/D48728
    Sponsored by:   Klara Inc.
---
 sys/kern/kern_umtx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sys/kern/kern_umtx.c b/sys/kern/kern_umtx.c
index a9294c324cb4..938dcf2ff1cb 100644
--- a/sys/kern/kern_umtx.c
+++ b/sys/kern/kern_umtx.c
@@ -3789,7 +3789,7 @@ do_sem2_wake(struct thread *td, struct _usem2 *sem)
                                rv = casueword32(&sem->_count, count, &count,
                                    count & ~USEM_HAS_WAITERS);
                                if (rv == 1) {
-                                       rv = thread_check_susp(td, true);
+                                       rv = thread_check_susp(td, false);
                                        if (rv != 0)
                                                break;
                                }