The patch titled
Subject: maple_tree: reset mas->index and mas->last on write retries
has been added to the -mm mm-unstable branch. Its filename is
maple_tree-reset-mas-index-and-mas-last-on-write-retries.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/maple_tree-reset-mas-index-and-mas-last-on-write-retries.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
Subject: maple_tree: reset mas->index and mas->last on write retries
Date: Mon, 12 Aug 2024 15:05:42 -0400
The following scenario can result in a race condition:
Consider a node with the following indices and values
a<------->b<----------->c<--------->d
0xA NULL 0xB
CPU 1 CPU 2
--------- ---------
mas_set_range(a,b)
mas_erase()
-> range is expanded (a,c) because of null expansion
mas_nomem()
mas_unlock()
mas_store_range(b,c,0xC)
The node now looks like:
a<------->b<----------->c<--------->d
0xA 0xC 0xB
mas_lock()
mas_erase() <------ range of erase is still (a,c)
The node is now NULL from (a,c) but the write from CPU 2 should have been
retained and range (b,c) should still have 0xC as its value. We can fix
this by re-intializing to the original index and last. This does not need
a cc: Stable as there are no users of the maple tree which use internal
locking and this condition is only possible with internal locking.
Link: https://lkml.kernel.org/r/20240812190543.71967-1-sidhartha.kumar@xxxxxxxxxx
Signed-off-by: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/maple_tree.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
--- a/lib/maple_tree.c~maple_tree-reset-mas-index-and-mas-last-on-write-retries
+++ a/lib/maple_tree.c
@@ -5451,14 +5451,19 @@ EXPORT_SYMBOL_GPL(mas_store);
*/
int mas_store_gfp(struct ma_state *mas, void *entry, gfp_t gfp)
{
+ unsigned long index = mas->index;
+ unsigned long last = mas->last;
MA_WR_STATE(wr_mas, mas, entry);
mas_wr_store_setup(&wr_mas);
trace_ma_write(__func__, mas, 0, entry);
retry:
mas_wr_store_entry(&wr_mas);
- if (unlikely(mas_nomem(mas, gfp)))
+ if (unlikely(mas_nomem(mas, gfp))) {
+ if (!entry)
+ __mas_set_range(mas, index, last);
goto retry;
+ }
if (unlikely(mas_is_err(mas)))
return xa_err(mas->node);
@@ -6245,23 +6250,26 @@ EXPORT_SYMBOL_GPL(mas_find_range_rev);
void *mas_erase(struct ma_state *mas)
{
void *entry;
+ unsigned long index = mas->index;
MA_WR_STATE(wr_mas, mas, NULL);
if (!mas_is_active(mas) || !mas_is_start(mas))
mas->status = ma_start;
- /* Retry unnecessary when holding the write lock. */
+write_retry:
entry = mas_state_walk(mas);
if (!entry)
return NULL;
-write_retry:
/* Must reset to ensure spanning writes of last slot are detected */
mas_reset(mas);
mas_wr_store_setup(&wr_mas);
mas_wr_store_entry(&wr_mas);
- if (mas_nomem(mas, GFP_KERNEL))
+ if (mas_nomem(mas, GFP_KERNEL)) {
+ /* in case the range of entry changed when unlocked */
+ mas->index = mas->last = index;
goto write_retry;
+ }
return entry;
}
_
Patches currently in -mm which might be from sidhartha.kumar@xxxxxxxxxx are
maple_tree-reset-mas-index-and-mas-last-on-write-retries.patch
maple_tree-add-test-to-replicate-low-memory-race-conditions.patch
