maple_tree: catch race in mas_alloc_cyclic()

If mas_alloc_cyclic() is called during a low memory situation, it is
possible the lock may be dropped so reclaim can occur.  There is a window
where some other task may allocate the same id and cause the mas_insert()
to fail with -EEXIST.  In this scenario the function will return -EEXIST,
which is not expected.

Modifying the retry on mas_nomem() to re-search for a slot means that any
race with other writes will not matter as the lock will be held between
finding the index and writing the index.

Moving the flag logic avoids cases where the flag is modified on drop
lock/reacquire or when the write fails after clearing the flag.

No existing users are exposed to this issue.

Link: https://lore.kernel.org/20260630190843.3563858-13-liam@infradead.org
Fixes: 9b6713cc7522 ("maple_tree: Add mtree_alloc_cyclic()")
Signed-off-by: Liam R. Howlett (Oracle) <liam@infradead.org>
Reported-by: Chris Mason <clm@meta.com>
Reviewed-by: Chuck Lever <cel@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Joe Perches <joe@perches.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

0 files changed, 0 insertions, 0 deletions