Hi Konstantin, On Tue, Jul 28, 2020 at 11:42 AM Konstantin Belousov <kostik...@gmail.com> wrote: > > On Fri, Jul 24, 2020 at 05:34:05PM +0000, Conrad Meyer wrote: > > ... > > --- head/sys/kern/vfs_bio.c Fri Jul 24 17:32:10 2020 (r363481) > > +++ head/sys/kern/vfs_bio.c Fri Jul 24 17:34:04 2020 (r363482) > > @@ -3849,7 +3849,7 @@ getblkx(struct vnode *vp, daddr_t blkno, daddr_t dblkn > > ... > > + /* Attempt lockless lookup first. */ > > + bp = gbincore_unlocked(bo, blkno); > > + if (bp == NULL) > > + goto newbuf_unlocked; > > + > > + lockflags = LK_EXCLUSIVE | LK_SLEEPFAIL | > > + ((flags & GB_LOCK_NOWAIT) ? LK_NOWAIT : 0); > > + > > + error = BUF_TIMELOCK(bp, lockflags, NULL, "getblku", slpflag, > > + slptimeo); > I realized that this is not safe. There is an ordering between buffer > types that defines which order buffer locks should obey. For instance, > on UFS the critical order is inode buffer -> snaplk -> cg buffer, or > data block -> indirect data block. Since buffer identity can change under > us, we might end up waiting for a lock of type that is incompatible with > the currently owned lock. > > I think the easiest fix is to use LK_NOWAIT always, after all it is lockless > path. ERESTART/EINTR checks below than can be removed.
Thanks, that makes sense to me. Please see https://reviews.freebsd.org/D25898 . (For the UFS scenario, I think this requires an on-disk sector changing identity from one kind to another? I believe lblknos are mostly statically typed in UFS, but it could happen with data blocks and indirect blocks? Of course, UFS is not the only filesystem.) Best regards, Conrad _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
