Messages in this thread | | | Date | Wed, 10 Dec 2008 07:40:58 +1000 | From | "Dave Airlie" <> | Subject | Re: [patch 021/104] lib/idr.c: fix rcu related race with idr_find |
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On Thu, Dec 4, 2008 at 5:49 AM, Greg KH <gregkh@suse.de> wrote: > 2.6.27-stable review patch. If anyone has any objections, please let us know. > Revert.
This caused problems in the F10 kernel with idr, the drm device alloc went all wierd, it might be a drm bug but changing this code triggers it and so it isn't really "stable"
Dave.
> ------------------ > From: Manfred Spraul <manfred@colorfullife.com> > > commit 6ff2d39b91aec3dcae951afa982059e3dd9b49dc upstream. > > 2nd part of the fixes needed for > http://bugzilla.kernel.org/show_bug.cgi?id=11796. > > When the idr tree is either grown or shrunk, then the update to the number > of layers and the top pointer were not atomic. This race caused crashes. > > The attached patch fixes that by replicating the layers counter in each > layer, thus idr_find doesn't need idp->layers anymore. > > Signed-off-by: Manfred Spraul <manfred@colorfullife.com> > Cc: Clement Calmels <cboulte@gmail.com> > Cc: Nadia Derbey <Nadia.Derbey@bull.net> > Cc: Pierre Peiffer <peifferp@gmail.com> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org> > Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> > Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> > > --- > include/linux/idr.h | 3 ++- > lib/idr.c | 14 ++++++++++++-- > 2 files changed, 14 insertions(+), 3 deletions(-) > > --- a/include/linux/idr.h > +++ b/include/linux/idr.h > @@ -52,13 +52,14 @@ struct idr_layer { > unsigned long bitmap; /* A zero bit means "space here" */ > struct idr_layer *ary[1<<IDR_BITS]; > int count; /* When zero, we can release it */ > + int layer; /* distance from leaf */ > struct rcu_head rcu_head; > }; > > struct idr { > struct idr_layer *top; > struct idr_layer *id_free; > - int layers; > + int layers; /* only valid without concurrent changes */ > int id_free_cnt; > spinlock_t lock; > }; > --- a/lib/idr.c > +++ b/lib/idr.c > @@ -185,6 +185,7 @@ static int sub_alloc(struct idr *idp, in > new = get_from_free_list(idp); > if (!new) > return -1; > + new->layer = l-1; > rcu_assign_pointer(p->ary[m], new); > p->count++; > } > @@ -210,6 +211,7 @@ build_up: > if (unlikely(!p)) { > if (!(p = get_from_free_list(idp))) > return -1; > + p->layer = 0; > layers = 1; > } > /* > @@ -237,6 +239,7 @@ build_up: > } > new->ary[0] = p; > new->count = 1; > + new->layer = layers-1; > if (p->bitmap == IDR_FULL) > __set_bit(0, &new->bitmap); > p = new; > @@ -493,17 +496,21 @@ void *idr_find(struct idr *idp, int id) > int n; > struct idr_layer *p; > > - n = idp->layers * IDR_BITS; > p = rcu_dereference(idp->top); > + if (!p) > + return NULL; > + n = (p->layer+1) * IDR_BITS; > > /* Mask off upper bits we don't use for the search. */ > id &= MAX_ID_MASK; > > if (id >= (1 << n)) > return NULL; > + BUG_ON(n == 0); > > while (n > 0 && p) { > n -= IDR_BITS; > + BUG_ON(n != p->layer*IDR_BITS); > p = rcu_dereference(p->ary[(id >> n) & IDR_MASK]); > } > return((void *)p); > @@ -582,8 +589,11 @@ void *idr_replace(struct idr *idp, void > int n; > struct idr_layer *p, *old_p; > > - n = idp->layers * IDR_BITS; > p = idp->top; > + if (!p) > + return ERR_PTR(-EINVAL); > + > + n = (p->layer+1) * IDR_BITS; > > id &= MAX_ID_MASK; > > > -- > 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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