Messages in this thread | | | From | Peter Staubach <> | Date | Mon, 23 Apr 2012 13:43:12 -0400 | Subject | RE: [PATCH RFC v3] vfs: make fstatat retry once on ESTALE errors from getattr call |
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The test program runs and expects many, many ENOENTS to be returned. It just doesn't expect ESTALE to be returned. It doesn't see ESTALE from local file systems.
To answer a question asked earlier -- the test program does not mimic any particular application behavior, except in the extreme. It is designed to create as stressful a situation as might be ever seen.
Has anyone explained why the full solution won't work from a technical viewpoint?
Thanx...
ps
-----Original Message----- From: Steve Dickson [mailto:SteveD@redhat.com] Sent: Monday, April 23, 2012 10:55 AM To: Jeff Layton Cc: linux-fsdevel@vger.kernel.org; linux-nfs@vger.kernel.org; linux-kernel@vger.kernel.org; miklos@szeredi.hu; viro@ZenIV.linux.org.uk; hch@infradead.org; michael.brantley@deshaw.com; sven.breuner@itwm.fraunhofer.de; chuck.lever@oracle.com; Peter Staubach; malahal@us.ibm.com; bfields@fieldses.org; trond.myklebust@fys.uio.no; rees@umich.edu Subject: Re: [PATCH RFC v3] vfs: make fstatat retry once on ESTALE errors from getattr call
On 04/20/2012 05:13 PM, Jeff Layton wrote: > On Fri, 20 Apr 2012 16:18:37 -0400 > Steve Dickson <SteveD@redhat.com> wrote: > >> On 04/20/2012 10:40 AM, Jeff Layton wrote: >>> I guess the questions at this point is: >>> >>> 1) How representative is Peter's mkdir_test() of a real-world workload? >> Reading your email I had to wonder the same thing... What application >> removes hierarchy of directories in a loop from two different clients? >> I would suspect not many, if any... esp over NFS... >> > > Peter's test just happens to demonstrate the problem well, but one > could envision someone removing a heirarchy of directories on the > server while we're trying to do other operations in it. At that point, > we can easily end up hitting an ESTALE twice while doing the lookup > and returning ESTALE back to userspace. Just curious, what happens when you run Peter's mkdir_test() on a local file system? Any errors returned?
I would think removing hierarchy of directories while they are being accessed has to even cause local fs some type of havoc
> >>> >>> 2) if we assume that it is fairly representative of one, how can we >>> achieve retrying indefinitely with NFS, or at least some large >>> finite amount? >> The amount of looping would be peer speculation. If the problem can >> not be handled by one simple retry I would say we simply pass the >> error up to the app... Its an application issue... >> > > It's not an application issue. The application just asked the kernel > to do an operation on a pathname. The only reason you're getting an > ESTALE back in this situation is a shortcoming of the implementation. > > We passed it a pathname after all, not a filehandle. ESTALE really has > no place as a return code in that situation... We'll have to agree to disagree... I think any application that is removing hierarchies of file and directory w/out taking any precautionary locking is a shortcoming of the application implementation. > >>> >>> I have my doubts as to whether it would really be as big a problem >>> for other filesystems as Miklos and others have asserted, but I'll >>> take their word for it at the moment. What's the best way to contain >>> this behavior to just those filesystems that want to retry >>> indefinitely when they get an ESTALE? Would we need to go with an >>> entirely new ESTALERETRY after all? >>> >> Introducing a new errno to handle this problem would be overkill IMHO... >> >> If we have to go to the looping approach, I would strong suggest we >> make the file systems register for this type of behavior... >> > > Returning ESTALERETRY would be registering for it in a way and it is > somewhat cleaner than having to go all the way back up to the fstype > to figure out whether you want to retry it or not. How would legacy apps handle this new errno, esp if they have logic to take care of ESTALE errors?
steved.
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