From: Jan Kara <jack@suse.cz> To: Johannes Weiner <hannes@cmpxchg.org> Cc: Andrew Morton <akpm@linux-foundation.org>, Jan Kara <jack@suse.cz>, "Kirill A. Shutemov" <kirill@shutemov.name>, Linus Torvalds <torvalds@linux-foundation.org>, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH 5/9] lib: radix-tree: check accounting of existing slot replacement users Date: Fri, 18 Nov 2016 08:46:38 +0100 [thread overview] Message-ID: <20161118074638.GE18676@quack2.suse.cz> (raw) In-Reply-To: <20161117193021.GB23430@cmpxchg.org> On Thu 17-11-16 14:30:21, Johannes Weiner wrote: > The bug in khugepaged fixed earlier in this series shows that radix > tree slot replacement is fragile; and it will become more so when not > only NULL<->!NULL transitions need to be caught but transitions from > and to exceptional entries as well. We need checks. > > Re-implement radix_tree_replace_slot() on top of the sanity-checked > __radix_tree_replace(). This requires existing callers to also pass > the radix tree root, but it'll warn us when somebody replaces slots > with contents that need proper accounting (transitions between NULL > entries, real entries, exceptional entries) and where a replacement > through the slot pointer would corrupt the radix tree node counts. > > Suggested-by: Jan Kara <jack@suse.cz> > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Looks good. You can add: Reviewed-by: Jan Kara <jack@suse.cz> One nit below: > @@ -785,6 +776,50 @@ void __radix_tree_replace(struct radix_tree_root *root, > } > > /** > + * __radix_tree_replace - replace item in a slot > + * @root: radix tree root > + * @node: pointer to tree node > + * @slot: pointer to slot in @node > + * @item: new item to store in the slot. > + * > + * For use with __radix_tree_lookup(). Caller must hold tree write locked > + * across slot lookup and replacement. > + */ I'd comment here that even this function cannot be used for NULL <-> non-NULL replacements. For that are radix_tree_delete() and radix_tree_insert(). Honza -- Jan Kara <jack@suse.com> SUSE Labs, CR
WARNING: multiple messages have this Message-ID (diff)
From: Jan Kara <jack@suse.cz> To: Johannes Weiner <hannes@cmpxchg.org> Cc: Andrew Morton <akpm@linux-foundation.org>, Jan Kara <jack@suse.cz>, "Kirill A. Shutemov" <kirill@shutemov.name>, Linus Torvalds <torvalds@linux-foundation.org>, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH 5/9] lib: radix-tree: check accounting of existing slot replacement users Date: Fri, 18 Nov 2016 08:46:38 +0100 [thread overview] Message-ID: <20161118074638.GE18676@quack2.suse.cz> (raw) In-Reply-To: <20161117193021.GB23430@cmpxchg.org> On Thu 17-11-16 14:30:21, Johannes Weiner wrote: > The bug in khugepaged fixed earlier in this series shows that radix > tree slot replacement is fragile; and it will become more so when not > only NULL<->!NULL transitions need to be caught but transitions from > and to exceptional entries as well. We need checks. > > Re-implement radix_tree_replace_slot() on top of the sanity-checked > __radix_tree_replace(). This requires existing callers to also pass > the radix tree root, but it'll warn us when somebody replaces slots > with contents that need proper accounting (transitions between NULL > entries, real entries, exceptional entries) and where a replacement > through the slot pointer would corrupt the radix tree node counts. > > Suggested-by: Jan Kara <jack@suse.cz> > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Looks good. You can add: Reviewed-by: Jan Kara <jack@suse.cz> One nit below: > @@ -785,6 +776,50 @@ void __radix_tree_replace(struct radix_tree_root *root, > } > > /** > + * __radix_tree_replace - replace item in a slot > + * @root: radix tree root > + * @node: pointer to tree node > + * @slot: pointer to slot in @node > + * @item: new item to store in the slot. > + * > + * For use with __radix_tree_lookup(). Caller must hold tree write locked > + * across slot lookup and replacement. > + */ I'd comment here that even this function cannot be used for NULL <-> non-NULL replacements. For that are radix_tree_delete() and radix_tree_insert(). Honza -- Jan Kara <jack@suse.com> SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2016-11-18 7:46 UTC|newest] Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-11-17 19:11 [PATCH 0/9] mm: workingset: radix tree subtleties & single-page file refaults v3 Johannes Weiner 2016-11-17 19:11 ` Johannes Weiner 2016-11-17 19:11 ` [PATCH 1/9] mm: khugepaged: close use-after-free race during shmem collapsing Johannes Weiner 2016-11-17 19:11 ` Johannes Weiner 2016-11-17 23:19 ` Kirill A. Shutemov 2016-11-17 23:19 ` Kirill A. Shutemov 2016-11-18 7:29 ` Jan Kara 2016-11-18 7:29 ` Jan Kara 2016-11-17 19:11 ` [PATCH 2/9] mm: khugepaged: fix radix tree node leak in shmem collapse error path Johannes Weiner 2016-11-17 19:11 ` Johannes Weiner 2016-11-17 23:21 ` Kirill A. Shutemov 2016-11-17 23:21 ` Kirill A. Shutemov 2016-11-18 7:30 ` Jan Kara 2016-11-18 7:30 ` Jan Kara 2016-11-17 19:11 ` [PATCH 3/9] mm: workingset: turn shadow node shrinker bugs into warnings Johannes Weiner 2016-11-17 19:11 ` Johannes Weiner 2016-11-18 7:32 ` Jan Kara 2016-11-18 7:32 ` Jan Kara 2016-11-17 19:29 ` [PATCH 4/9] lib: radix-tree: native accounting of exceptional entries Johannes Weiner 2016-11-17 19:29 ` Johannes Weiner 2016-11-18 7:39 ` Jan Kara 2016-11-18 7:39 ` Jan Kara 2016-11-17 19:30 ` [PATCH 5/9] lib: radix-tree: check accounting of existing slot replacement users Johannes Weiner 2016-11-17 19:30 ` Johannes Weiner 2016-11-18 7:46 ` Jan Kara [this message] 2016-11-18 7:46 ` Jan Kara 2016-11-17 19:30 ` [PATCH 6/9] lib: radix-tree: add entry deletion support to __radix_tree_replace() Johannes Weiner 2016-11-17 19:30 ` Johannes Weiner 2016-11-18 8:13 ` Jan Kara 2016-11-18 8:13 ` Jan Kara 2016-11-17 19:31 ` [PATCH 7/9] lib: radix-tree: update callback for changing leaf nodes Johannes Weiner 2016-11-17 19:31 ` Johannes Weiner 2016-11-18 8:26 ` Jan Kara 2016-11-18 8:26 ` Jan Kara 2016-11-17 19:32 ` [PATCH 8/9] mm: workingset: move shadow entry tracking to radix tree exceptional tracking Johannes Weiner 2016-11-17 19:32 ` Johannes Weiner 2016-11-18 8:29 ` Jan Kara 2016-11-18 8:29 ` Jan Kara 2016-11-17 19:32 ` [PATCH 9/9] mm: workingset: restore refault tracking for single-page files Johannes Weiner 2016-11-17 19:32 ` Johannes Weiner 2016-11-18 8:30 ` Jan Kara 2016-11-18 8:30 ` Jan Kara
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