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Date: Fri, 11 Feb 2011 11:49:29 +0800 From: Ian Kent <raven@...maw.net> To: "J. R. Okajima" <hooanon05@...oo.co.jp> Cc: Nick Piggin <npiggin@...il.com>, Santosh Shilimkar <santosh.shilimkar@...com>, Mark Brown <broonie@...nsource.wolfsonmicro.com>, Trond Myklebust <Trond.Myklebust@...app.com>, Nick Piggin <npiggin@...nel.dk>, linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org Subject: Re: vfs-scale, general questions (Re: NFS root lockups with -next 20110113) On Wed, 2011-01-19 at 15:43 +0900, J. R. Okajima wrote: > Hi, > > Nick Piggin: > > Thanks for your help, can you see how I've fixed it in my vfs-scale > > tree? What do you think? > > Your fix is great. I have no objection at all. > Other than the fix, here are more generic questions about vfs-scale work. > I am happy if you reply when you have time. > > - getcwd(2) needs d_lock? > It acquires rename_lock and then tests whether the pwd is removed by > d_unhashed(). If a race condition between vfs_rename_dir() which may > unhash/rehash the dentry happens, then getcwd() may return the wrong > result due to unprotected d_unhashed() call, I am afraid. rename_lock > doesn't help this case. > > - what is the right order of dget() and mntget()? > If I remember correctly, someone said "mntget() first and then > dget(). when putting, do in reverse" in the discussion when > path_{get,put}() were born. So it is called "the right order" in the > commit log. > It was many years ago. Is it still true? And should rcu-walk follow it > too? The current implementation doesn't seem to care about this order. I didn't spot that, where did you see this? I'm not sure about the get but I fairly sure the dput() has to be before the mntput() because the shrink_dcache_*() cleanup routines object to dentrys that have a reference count of more than one. Ian -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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