Messages in this thread | | | Date | Tue, 04 May 2004 20:21:21 +1000 | From | Greg Banks <> | Subject | Re: d_splice_alias() problem. |
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G'day Dipankar,
I don't know if you've been following this thread on lkml, but Al Viro wants an RCU expert's opinion on the following dcache patch.
Greg Banks wrote: > > > > * Dentry_stat.nr_unused can be be spuriously decremented when dput() > > > races with __dget_unlocked(). Eventual result is nr_unused<0 > > > and kswapd loops. This is the problem I mentioned earlier. Note > > > that this is not an NFS-specific problem. Fix is: > > > [...first attempt elided...] > Ok, how about this...it's portable, and not racy, but may perturb the > logic slightly by also taking dentries off the unused list in the case > where they already had d_count>=1. I'm not sure how significant that is. > In any case this also passes my tests. > > --- linux.orig/fs/dcache.c Mon May 3 21:46:30 2004 > +++ linux/fs/dcache.c Tue May 4 14:34:44 2004 > @@ -256,7 +256,7 @@ > static inline struct dentry * __dget_locked(struct dentry *dentry) > { > atomic_inc(&dentry->d_count); > - if (atomic_read(&dentry->d_count) == 1) { > + if (!list_empty(&dentry->d_lru)) { > dentry_stat.nr_unused--; > list_del_init(&dentry->d_lru); > } > @@ -663,6 +663,7 @@ > if (gfp_mask & __GFP_FS) > prune_dcache(nr); > } > + BUG_ON(dentry_stat.nr_unused < 0); > return dentry_stat.nr_unused; > } >
viro@parcelfarce.linux.theplanet.co.uk wrote: > > a) ask RCU folks to review - the current logics in dcache.c is extremely > brittle as it is.
Greg. -- Greg Banks, R&D Software Engineer, SGI Australian Software Group. I don't speak for SGI. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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