The patch titled Subject: maple_tree: disable mas_wr_append() when other readers are possible has been added to the -mm mm-hotfixes-unstable branch. Its filename is maple_tree-disable-mas_wr_append-when-other-readers-are-possible.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days
------------------------------------------------------ From: "Liam R. Howlett" Liam.Howlett@oracle.com Subject: maple_tree: disable mas_wr_append() when other readers are possible Date: Fri, 18 Aug 2023 20:43:55 -0400
The current implementation of append may cause duplicate data and/or incorrect ranges to be returned to a reader during an update. Although this has not been reported or seen, disable the append write operation while the tree is in rcu mode out of an abundance of caution.
During the analysis of the mas_next_slot() the following was artificially created by separating the writer and reader code:
Writer: reader: mas_wr_append set end pivot updates end metata Detects write to last slot last slot write is to start of slot store current contents in slot overwrite old end pivot mas_next_slot(): read end metadata read old end pivot return with incorrect range store new value
Alternatively:
Writer: reader: mas_wr_append set end pivot updates end metata Detects write to last slot last lost write to end of slot store value mas_next_slot(): read end metadata read old end pivot read new end pivot return with incorrect range set old end pivot
There may be other accesses that are not safe since we are now updating both metadata and pointers, so disabling append if there could be rcu readers is the safest action.
Link: https://lkml.kernel.org/r/20230819004356.1454718-2-Liam.Howlett@oracle.com Fixes: 54a611b60590 ("Maple Tree: add new data structure") Signed-off-by: Liam R. Howlett Liam.Howlett@oracle.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
lib/maple_tree.c | 7 +++++++ 1 file changed, 7 insertions(+)
--- a/lib/maple_tree.c~maple_tree-disable-mas_wr_append-when-other-readers-are-possible +++ a/lib/maple_tree.c @@ -4265,6 +4265,10 @@ static inline unsigned char mas_wr_new_e * mas_wr_append: Attempt to append * @wr_mas: the maple write state * + * This is currently unsafe in rcu mode since the end of the node may be cached + * by readers while the node contents may be updated which could result in + * inaccurate information. + * * Return: True if appended, false otherwise */ static inline bool mas_wr_append(struct ma_wr_state *wr_mas) @@ -4274,6 +4278,9 @@ static inline bool mas_wr_append(struct struct ma_state *mas = wr_mas->mas; unsigned char node_pivots = mt_pivots[wr_mas->type];
+ if (mt_in_rcu(mas->tree)) + return false; + if (mas->offset != wr_mas->node_end) return false;
_
Patches currently in -mm which might be from Liam.Howlett@oracle.com are
maple_tree-disable-mas_wr_append-when-other-readers-are-possible.patch maple_tree-add-hex-output-to-maple_arange64-dump.patch maple_tree-reorder-replacement-of-nodes-to-avoid-live-lock.patch maple_tree-introduce-mas_put_in_tree.patch maple_tree-introduce-mas_tree_parent-definition.patch maple_tree-change-mas_adopt_children-parent-usage.patch maple_tree-replace-data-before-marking-dead-in-split-and-spanning-store.patch