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maple_tree: document that erase may use GFP_KERNEL for allocations

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State that the mas_erase() and mtree_erase() functions may use GFP_KERNEL
on allocation retry.  Don't just depend on people reading the
documentation by adding a check that will warn of the use.

Link: https://lore.kernel.org/20260821192627.4085470-14-liam@infradead.org
Signed-off-by: Liam R. Howlett (Oracle) <liam@infradead.org>
Reviewed-by: Rik van Riel <riel@surriel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Chris Mason <clm@meta.com>
Cc: Chuck Lever <cel@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Joe Perches <joe@perches.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Liam R. Howlett (Oracle)
2026-08-21 15:26:21 -04:00
committed by Andrew Morton
parent 35f1342e5b
commit 3f06ef1f34
1 changed files with 21 additions and 2 deletions
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23
lib/maple_tree.c
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@@ -5658,6 +5658,10 @@ EXPORT_SYMBOL_GPL(mas_find_range_rev);
* Searches for @mas->index, sets @mas->index and @mas->last to the range and
* erases that range.
*
* Note that erase requires allocations and will use GFP_KERNEL to do so if
* necessary. If the allocation fails, the internal lock will be dropped to
* retry.
*
* Return: the entry that was erased or %NULL, @mas->index and @mas->last are updated.
*/
void *mas_erase(struct ma_state *mas)
@@ -5666,13 +5670,21 @@ void *mas_erase(struct ma_state *mas)
unsigned long index = mas->index;
MA_WR_STATE(wr_mas, mas, NULL);
/*
* In low memory situations, the allocation is retried with the gfp flag
* GFP_KERNEL. The internal spinlock is dropped in mas_nomem(), however
* the external lock is not dropped.
*/
if (mt_external_lock(mas->tree))
might_alloc(GFP_KERNEL);
if (!mas_is_active(mas) || !mas_is_start(mas))
mas->status = ma_start;
write_retry:
entry = mas_state_walk(mas);
if (!entry)
return NULL;
goto out;
/* Must reset to ensure spanning writes of last slot are detected */
mas_reset(mas);
@@ -5683,8 +5695,10 @@ void *mas_erase(struct ma_state *mas)
goto write_retry;
}
if (mas_is_err(mas))
if (mas_is_err(mas)) {
entry = NULL;
goto out;
}
mas_wr_store_entry(&wr_mas);
out:
@@ -6012,6 +6026,10 @@ EXPORT_SYMBOL(mtree_alloc_rrange);
* Erasing is the same as a walk to an entry then a store of a NULL to that
* ENTIRE range. In fact, it is implemented as such using the advanced API.
*
* Note that erase requires allocations and will use GFP_KERNEL to do so if
* necessary. If the allocation fails, the internal lock will be dropped to
* retry.
*
* Return: The entry stored at the @index or %NULL
*/
void *mtree_erase(struct maple_tree *mt, unsigned long index)
@@ -6021,6 +6039,7 @@ void *mtree_erase(struct maple_tree *mt, unsigned long index)
MA_STATE(mas, mt, index, index);
trace_ma_op(TP_FCT, &mas);
might_alloc(GFP_KERNEL);
mtree_lock(mt);
entry = mas_erase(&mas);
mtree_unlock(mt);