git: a332ba32d4a2 - main - getblk: fail faster with GB_LOCK_NOWAIT

[Ryan Libby]

The branch main has been updated by rlibby:

URL: 
https://cgit.FreeBSD.org/src/commit/?id=a332ba32d4a26e20c959db14afa11ccfa25cf76c

commit a332ba32d4a26e20c959db14afa11ccfa25cf76c
Author:     Ryan Libby <rli...@freebsd.org>
AuthorDate: 2024-05-21 17:21:50 +0000
Commit:     Ryan Libby <rli...@freebsd.org>
CommitDate: 2024-05-21 17:21:50 +0000

    getblk: fail faster with GB_LOCK_NOWAIT
    
    If we asked not to wait on a lock, and then we failed to get a buf lock
    because we would have had to wait, then just return the error.  This
    avoids taking the bufobj lock and a second trip to lockmgr.
    
    Reviewed by:    mckusick, kib, markj
    Sponsored by:   Dell EMC Isilon
    Differential Revision:  https://reviews.freebsd.org/D45245
---
 sys/kern/vfs_bio.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/sys/kern/vfs_bio.c b/sys/kern/vfs_bio.c
index b5466fb2cd53..01057072d991 100644
--- a/sys/kern/vfs_bio.c
+++ b/sys/kern/vfs_bio.c
@@ -4010,8 +4010,23 @@ getblkx(struct vnode *vp, daddr_t blkno, daddr_t dblkno, 
int size, int slpflag,
 
        error = BUF_TIMELOCK(bp, LK_EXCLUSIVE | LK_NOWAIT, NULL, "getblku", 0,
            0);
-       if (error != 0)
+       if (error != 0) {
+               KASSERT(error == EBUSY,
+                   ("getblk: unexpected error %d from buf try-lock", error));
+               /*
+                * We failed a buf try-lock.
+                *
+                * With GB_LOCK_NOWAIT, just return, rather than taking the
+                * bufobj interlock and trying again, since we would probably
+                * fail again anyway.  This is okay even if the buf's identity
+                * changed and we contended on the wrong lock, as changing
+                * identity itself requires the buf lock, and we could have
+                * contended on the right lock.
+                */
+               if ((flags & GB_LOCK_NOWAIT) != 0)
+                       return (error);
                goto loop;
+       }
 
        /* Verify buf identify has not changed since lookup. */
        if (bp->b_bufobj == bo && bp->b_lblkno == blkno)
@@ -4020,6 +4035,10 @@ getblkx(struct vnode *vp, daddr_t blkno, daddr_t dblkno, 
int size, int slpflag,
        /* It changed, fallback to locked lookup. */
        BUF_UNLOCK_RAW(bp);
 
+       /* As above, with GB_LOCK_NOWAIT, just return. */
+       if ((flags & GB_LOCK_NOWAIT) != 0)
+               return (EBUSY);
+
 loop:
        BO_RLOCK(bo);
        bp = gbincore(bo, blkno);