git: cec3990d3479 - stable/13 - vm_reserv: Fix list locking in vm_reserv_reclaim_contig()

[Mark Johnston]

The branch stable/13 has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=cec3990d347972c30558b135b1bc9954184fb5fe

commit cec3990d347972c30558b135b1bc9954184fb5fe
Author:     Mark Johnston <markjdb at gmail.com>
AuthorDate: 2021-03-11 15:34:28 +0000
Commit:     Mark Johnston <markj at FreeBSD.org>
CommitDate: 2021-03-14 01:09:29 +0000

    vm_reserv: Fix list locking in vm_reserv_reclaim_contig()
    
    The per-domain partpop queue is locked by the combination of the
    per-domain lock and individual reservation mutexes.
    vm_reserv_reclaim_contig() scans the queue looking for partially
    populated reservations that can be reclaimed in order to satisfy the
    caller's allocation.
    
    During the scan, we drop the per-domain lock.  At this point, the rvn
    pointer may be invalidated.  Take care to load rvn after re-acquiring
    the per-domain lock.
    
    While here, simplify the condition used to check whether a reservation
    was dequeued while the per-domain lock was dropped.
    
    Reviewed by:    alc, kib
    Reported by:    gallatin
    Sponsored by:   The FreeBSD Foundation
    Differential Revision:  https://reviews.freebsd.org/D29203
    
    (cherry picked from commit 968079f253c11433d47bece4b41b46fcbf985903)
---
 sys/vm/vm_reserv.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/sys/vm/vm_reserv.c b/sys/vm/vm_reserv.c
index e7f542a66fdb..a9602c3977df 100644
--- a/sys/vm/vm_reserv.c
+++ b/sys/vm/vm_reserv.c
@@ -1344,8 +1344,8 @@ vm_reserv_reclaim_contig(int domain, u_long npages, vm_paddr_t low,
 			TAILQ_INSERT_AFTER(queue, rv, marker, partpopq);
 			vm_reserv_domain_unlock(domain);
 			vm_reserv_lock(rv);
-			if (!rv->inpartpopq ||
-			    TAILQ_NEXT(rv, partpopq) != marker) {
+			if (TAILQ_PREV(marker, vm_reserv_queue, partpopq) !=
+			    rv) {
 				vm_reserv_unlock(rv);
 				vm_reserv_domain_lock(domain);
 				rvn = TAILQ_NEXT(marker, partpopq);
@@ -1363,8 +1363,9 @@ vm_reserv_reclaim_contig(int domain, u_long npages, vm_paddr_t low,
 			vm_reserv_unlock(rv);
 			return (true);
 		}
-		vm_reserv_unlock(rv);
 		vm_reserv_domain_lock(domain);
+		rvn = TAILQ_NEXT(rv, partpopq);
+		vm_reserv_unlock(rv);
 	}
 	vm_reserv_domain_unlock(domain);
 	vm_reserv_domain_scan_unlock(domain);