* [PATCH] radix-tree: Fix private list warnings
@ 2017-01-13 1:28 Matthew Wilcox
2017-01-14 15:42 ` Johannes Weiner
0 siblings, 1 reply; 5+ messages in thread
From: Matthew Wilcox @ 2017-01-13 1:28 UTC (permalink / raw)
To: Johannes Weiner, Linus Torvalds
Cc: Matthew Wilcox, Andrew Morton, linux-kernel
From: Matthew Wilcox <mawilcox@microsoft.com>
The newly introduced warning in radix_tree_free_nodes() was testing the
wrong variable; it should have been 'old' instead of 'node'. Rather
than replace that one instance, I noticed that we can simply put the
WARN_ON_ONCE in radix_tree_node_free() and it will be just as effective.
Fixes: ea07b862ac8e ("mm: workingset: fix use-after-free in shadow node shrinker")
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
---
lib/radix-tree.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 4a4ed3ee4222..3c4577cabc57 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -449,6 +449,7 @@ static void radix_tree_node_rcu_free(struct rcu_head *head)
static inline void
radix_tree_node_free(struct radix_tree_node *node)
{
+ WARN_ON_ONCE(!list_empty(&node->private_list));
call_rcu(&node->rcu_head, radix_tree_node_rcu_free);
}
@@ -734,7 +735,6 @@ static inline void radix_tree_shrink(struct radix_tree_root *root,
update_node(node, private);
}
- WARN_ON_ONCE(!list_empty(&node->private_list));
radix_tree_node_free(node);
}
}
@@ -766,7 +766,6 @@ static void delete_node(struct radix_tree_root *root,
root->rnode = NULL;
}
- WARN_ON_ONCE(!list_empty(&node->private_list));
radix_tree_node_free(node);
node = parent;
@@ -868,7 +867,6 @@ static void radix_tree_free_nodes(struct radix_tree_node *node)
struct radix_tree_node *old = child;
offset = child->offset + 1;
child = child->parent;
- WARN_ON_ONCE(!list_empty(&node->private_list));
radix_tree_node_free(old);
if (old == entry_to_node(node))
return;
--
2.11.0.296.g5800ad326.dirty
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] radix-tree: Fix private list warnings
2017-01-13 1:28 [PATCH] radix-tree: Fix private list warnings Matthew Wilcox
@ 2017-01-14 15:42 ` Johannes Weiner
2017-01-14 21:31 ` Matthew Wilcox
0 siblings, 1 reply; 5+ messages in thread
From: Johannes Weiner @ 2017-01-14 15:42 UTC (permalink / raw)
To: Matthew Wilcox
Cc: Linus Torvalds, Matthew Wilcox, Andrew Morton, linux-kernel
On Thu, Jan 12, 2017 at 05:28:23PM -0800, Matthew Wilcox wrote:
> From: Matthew Wilcox <mawilcox@microsoft.com>
>
> The newly introduced warning in radix_tree_free_nodes() was testing the
> wrong variable; it should have been 'old' instead of 'node'. Rather
> than replace that one instance, I noticed that we can simply put the
> WARN_ON_ONCE in radix_tree_node_free() and it will be just as effective.
>
> Fixes: ea07b862ac8e ("mm: workingset: fix use-after-free in shadow node shrinker")
> Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Thanks for the fix in radix_tree_free_nodes(). But I intentionally
spread out the warnings to retain the line numbers. The inlining in
that code will obscure which tree operation ends up triggering.
^ permalink raw reply [flat|nested] 5+ messages in thread
* RE: [PATCH] radix-tree: Fix private list warnings
2017-01-14 15:42 ` Johannes Weiner
@ 2017-01-14 21:31 ` Matthew Wilcox
2017-01-15 0:57 ` Johannes Weiner
0 siblings, 1 reply; 5+ messages in thread
From: Matthew Wilcox @ 2017-01-14 21:31 UTC (permalink / raw)
To: Johannes Weiner, Matthew Wilcox
Cc: Linus Torvalds, Andrew Morton, linux-kernel
From: Johannes Weiner [mailto:hannes@cmpxchg.org]
> On Thu, Jan 12, 2017 at 05:28:23PM -0800, Matthew Wilcox wrote:
> > The newly introduced warning in radix_tree_free_nodes() was testing the
> > wrong variable; it should have been 'old' instead of 'node'. Rather
> > than replace that one instance, I noticed that we can simply put the
> > WARN_ON_ONCE in radix_tree_node_free() and it will be just as effective.
> >
> > Fixes: ea07b862ac8e ("mm: workingset: fix use-after-free in shadow node
> shrinker")
> > Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
>
> Thanks for the fix in radix_tree_free_nodes(). But I intentionally
> spread out the warnings to retain the line numbers. The inlining in
> that code will obscure which tree operation ends up triggering.
The backtrace should make that fairly obvious though; even if radix_tree_node_free() gets inlined, the caller of radix_tree_free_nodes() probably doesn't also call radix_tree_shrink() or delete_node(). You're really looking for the caller in the backtrace that's outside of radix-tree.c.
By the way, if you'd run the radix tree test-suite, the WARN_ON_ONCE would have triggered (that's how I spotted the bug). The test-suite is getting pretty useful these days; would you mind running it in future?
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] radix-tree: Fix private list warnings
2017-01-14 21:31 ` Matthew Wilcox
@ 2017-01-15 0:57 ` Johannes Weiner
2017-01-18 16:37 ` Johannes Weiner
0 siblings, 1 reply; 5+ messages in thread
From: Johannes Weiner @ 2017-01-15 0:57 UTC (permalink / raw)
To: Matthew Wilcox
Cc: Matthew Wilcox, Linus Torvalds, Andrew Morton, linux-kernel
On Sat, Jan 14, 2017 at 09:31:51PM +0000, Matthew Wilcox wrote:
> From: Johannes Weiner [mailto:hannes@cmpxchg.org]
> > On Thu, Jan 12, 2017 at 05:28:23PM -0800, Matthew Wilcox wrote:
> > > The newly introduced warning in radix_tree_free_nodes() was testing the
> > > wrong variable; it should have been 'old' instead of 'node'. Rather
> > > than replace that one instance, I noticed that we can simply put the
> > > WARN_ON_ONCE in radix_tree_node_free() and it will be just as effective.
> > >
> > > Fixes: ea07b862ac8e ("mm: workingset: fix use-after-free in shadow node
> > shrinker")
> > > Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
> >
> > Thanks for the fix in radix_tree_free_nodes(). But I intentionally
> > spread out the warnings to retain the line numbers. The inlining in
> > that code will obscure which tree operation ends up triggering.
>
> The backtrace should make that fairly obvious though; even if
> radix_tree_node_free() gets inlined, the caller of
> radix_tree_free_nodes() probably doesn't also call
> radix_tree_shrink() or delete_node(). You're really looking for the
> caller in the backtrace that's outside of radix-tree.c.
Distinguishing between the radix_tree_shrink() and the delete_node()
sites was essential to find the bug whose fix added these warnings.
The former gets inlined into the latter. Not impossible to figure out
which one triggered from a full dump, but certainly less robust.
> By the way, if you'd run the radix tree test-suite, the WARN_ON_ONCE
> would have triggered (that's how I spotted the bug). The test-suite
> is getting pretty useful these days; would you mind running it in
> future?
Thanks, I'll keep that in mind for future radix tree changes.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] radix-tree: Fix private list warnings
2017-01-15 0:57 ` Johannes Weiner
@ 2017-01-18 16:37 ` Johannes Weiner
0 siblings, 0 replies; 5+ messages in thread
From: Johannes Weiner @ 2017-01-18 16:37 UTC (permalink / raw)
To: Matthew Wilcox
Cc: Matthew Wilcox, Linus Torvalds, Andrew Morton, linux-kernel
On Sat, Jan 14, 2017 at 07:57:51PM -0500, Johannes Weiner wrote:
> On Sat, Jan 14, 2017 at 09:31:51PM +0000, Matthew Wilcox wrote:
> > From: Johannes Weiner [mailto:hannes@cmpxchg.org]
> > > On Thu, Jan 12, 2017 at 05:28:23PM -0800, Matthew Wilcox wrote:
> > > > The newly introduced warning in radix_tree_free_nodes() was testing the
> > > > wrong variable; it should have been 'old' instead of 'node'. Rather
> > > > than replace that one instance, I noticed that we can simply put the
> > > > WARN_ON_ONCE in radix_tree_node_free() and it will be just as effective.
> > > >
> > > > Fixes: ea07b862ac8e ("mm: workingset: fix use-after-free in shadow node
> > > shrinker")
> > > > Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
> > >
> > > Thanks for the fix in radix_tree_free_nodes(). But I intentionally
> > > spread out the warnings to retain the line numbers. The inlining in
> > > that code will obscure which tree operation ends up triggering.
> >
> > The backtrace should make that fairly obvious though; even if
> > radix_tree_node_free() gets inlined, the caller of
> > radix_tree_free_nodes() probably doesn't also call
> > radix_tree_shrink() or delete_node(). You're really looking for the
> > caller in the backtrace that's outside of radix-tree.c.
>
> Distinguishing between the radix_tree_shrink() and the delete_node()
> sites was essential to find the bug whose fix added these warnings.
> The former gets inlined into the latter. Not impossible to figure out
> which one triggered from a full dump, but certainly less robust.
This?
>From 669b5ed6e32386d634023fee29b0b8562951e734 Mon Sep 17 00:00:00 2001
From: Matthew Wilcox <mawilcox@microsoft.com>
Date: Thu, 12 Jan 2017 17:28:23 -0800
Subject: [PATCH] radix-tree: Fix private list warnings
The newly introduced warning in radix_tree_free_nodes() was testing the
wrong variable; it should have been 'old' instead of 'node'.
Fixes: ea07b862ac8e ("mm: workingset: fix use-after-free in shadow node shrinker")
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
lib/radix-tree.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 0b92d605fb69..84812a9fb16f 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -769,7 +769,7 @@ static void radix_tree_free_nodes(struct radix_tree_node *node)
struct radix_tree_node *old = child;
offset = child->offset + 1;
child = child->parent;
- WARN_ON_ONCE(!list_empty(&node->private_list));
+ WARN_ON_ONCE(!list_empty(&old->private_list));
radix_tree_node_free(old);
if (old == entry_to_node(node))
return;
--
2.11.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
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2017-01-13 1:28 [PATCH] radix-tree: Fix private list warnings Matthew Wilcox
2017-01-14 15:42 ` Johannes Weiner
2017-01-14 21:31 ` Matthew Wilcox
2017-01-15 0:57 ` Johannes Weiner
2017-01-18 16:37 ` Johannes Weiner
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