git: fd6ca665d206 - main - Fix umtxq_sleep() regression caused by 56070dd2e4d.

The branch main has been updated by mav:

URL: https://cgit.FreeBSD.org/src/commit/?id=fd6ca665d206b74970e7c01d06ae06fed71500fc

commit fd6ca665d206b74970e7c01d06ae06fed71500fc
Author:     Alexander Motin <mav@FreeBSD.org>
AuthorDate: 2022-03-21 23:43:39 +0000
Commit:     Alexander Motin <mav@FreeBSD.org>
CommitDate: 2022-03-21 23:55:55 +0000

    Fix umtxq_sleep() regression caused by 56070dd2e4d.
    
    umtxq_requeue() moves the queue to a different hash chain and different
    lock, so we can't rely on msleep_sbt() reacquiring the same old lock.
    We have to use PDROP and update the queue chain and so lock pointer.
    
    PR:             262587
    MFC after:      2 weeks
---
 sys/kern/kern_umtx.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/sys/kern/kern_umtx.c b/sys/kern/kern_umtx.c
index b864e6fe9e49..7f74ba68b59c 100644
--- a/sys/kern/kern_umtx.c
+++ b/sys/kern/kern_umtx.c
@@ -808,8 +808,10 @@ umtxq_sleep(struct umtx_q *uq, const char *wmesg,
 			if (error != 0)
 				break;
 		}
-		error = msleep_sbt(uq, &uc->uc_lock, PCATCH, wmesg,
+		error = msleep_sbt(uq, &uc->uc_lock, PCATCH | PDROP, wmesg,
 		    sbt, 0, flags);
+		uc = umtxq_getchain(&uq->uq_key);
+		mtx_lock(&uc->uc_lock);
 		if (error == EINTR || error == ERESTART)
 			break;
 		if (error == EWOULDBLOCK && (flags & C_ABSOLUTE) != 0) {