Date: Tue, 21 Oct 2025 06:28:20 -0700 From: Rick Macklem <rick.macklem@gmail.com> To: "Peter 'PMc' Much" <pmc@citylink.dinoex.sub.org> Cc: freebsd-fs@freebsd.org Subject: Re: Why does rangelock_enqueue() hang for hours? Message-ID: <CAM5tNy6n5QJpRpkCJFHK=_5dWT=EZqkjztAfZHdqREKYSby55g@mail.gmail.com> In-Reply-To: <aPeEVSamcdKSoF5N@disp.intra.daemon.contact>
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On Tue, Oct 21, 2025 at 6:09 AM Peter 'PMc' Much <pmc@citylink.dinoex.sub.org> wrote: > > > This is 14.3-RELEASE. > > I am copying a file from a NFSv4 share to a local filesystem. This > takes a couple of hours. > > In the meantime I want to read that partially copied file. This is > not possible. The reading process locks up in rangelock_enqueue(), > unkillable(!), and only after the first slow copy has completed, it > will do it's job. > > Even if I do the first copy to stdout with redirect to file, the > same problem happens. I.e.: > > $ cat /nfsshare/File > /localfs/File & > $ cat /localfs/File --> HANGS unkillable This is caused by "cat" using copy_file_range(2), where the system call is taking a long time. The version done below makes "cat" not use copy_file_range(2). (copy_file_range(2) is interruptible, but that stops the file copy. It also has a "return after 1sec" option. Maybe that option should be exposed to userland and used by "cat", "cp" and friends at least when enabled by a command line option. (I'll admit looking at a file while it is being copied is a bit odd?) The whole idea behind range-lock is to prevent a read/write syscall from seeing a partial write. It just happens that the "write" takes a long time in this case. Do others have thoughts on this? rick > > Only if I introduce another process, the tie is avoided: > > $ cat /nfsshare/File | cat > /localfs/File & > $ cat /localfs/File --> WORKS > > I very much doubt that this is how it should be. > > Also, if I try to get some information about the supposed operation > of this "rangelock" feature, search engines point me to a > "rangelock(9)" manpage on man.freebsd.org, but that page doesn't > seem to exist. :( >help
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