Commit 309e02dc authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

ublk: avoid unpinning pages under maple tree spinlock 



ublk_shmem_remove_ranges() calls unpin_user_pages() while holding the
maple tree spinlock (mas_lock). Although unpin_user_pages() is safe in
atomic context, holding the spinlock across potentially many page
unpinning operations is not ideal.

Split into __ublk_shmem_remove_ranges() which erases up to 64 ranges
under mas_lock, collecting base_pfn and nr_pages into a temporary
xarray. Then drop the lock and unpin pages outside spinlock context.
ublk_shmem_remove_ranges() loops until all matching ranges are
processed.

Signed-off-by: default avatarMing Lei <tom.leiming@gmail.com>
Link: https://patch.msgid.link/20260423033058.2805135-4-tom.leiming@gmail.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent ea1db795

drivers/block/ublk_drv.c

+46 −10
Original line number Diff line number Diff line
@@ -5441,32 +5441,68 @@ static void ublk_unpin_range_pages(unsigned long base_pfn, 
}



/*

 * Remove ranges from the maple tree matching buf_index, unpin pages

 * and free range structs. If buf_index < 0, remove all ranges.

 * Inner loop: erase up to UBLK_REMOVE_BATCH matching ranges under

 * mas_lock, collecting them into an xarray. Then drop the lock and

 * unpin pages + free ranges outside spinlock context.

 *

 * Returns true if the tree walk completed, false if more ranges remain.

 * Xarray key is the base PFN, value encodes nr_pages via xa_mk_value().

 */

static int ublk_shmem_remove_ranges(struct ublk_device *ub, int buf_index)

#define UBLK_REMOVE_BATCH	64



static bool __ublk_shmem_remove_ranges(struct ublk_device *ub,

					int buf_index, int *ret)

{

	MA_STATE(mas, &ub->buf_tree, 0, ULONG_MAX);

	struct ublk_buf_range *range;

	int ret = -ENOENT;

	struct xarray to_unpin;

	unsigned long idx;

	unsigned int count = 0;

	bool done = false;

	void *entry;



	xa_init(&to_unpin);



	mas_lock(&mas);

	mas_for_each(&mas, range, ULONG_MAX) {

		unsigned long base, nr;

		unsigned long nr;



		if (buf_index >= 0 && range->buf_index != buf_index)

			continue;



		ret = 0;

		base = mas.index;

		nr = mas.last - base + 1;

		*ret = 0;

		nr = mas.last - mas.index + 1;

		if (xa_err(xa_store(&to_unpin, mas.index,

				    xa_mk_value(nr), GFP_ATOMIC)))

			goto unlock;

		mas_erase(&mas);



		ublk_unpin_range_pages(base, nr);

		kfree(range);

		if (++count >= UBLK_REMOVE_BATCH)

			goto unlock;

	}

	done = true;

unlock:

	mas_unlock(&mas);



	xa_for_each(&to_unpin, idx, entry)

		ublk_unpin_range_pages(idx, xa_to_value(entry));

	xa_destroy(&to_unpin);



	return done;

}



/*

 * Remove ranges from the maple tree matching buf_index, unpin pages

 * and free range structs. If buf_index < 0, remove all ranges.

 * Processes ranges in batches to avoid holding the maple tree spinlock

 * across potentially expensive page unpinning.

 */

static int ublk_shmem_remove_ranges(struct ublk_device *ub, int buf_index)

{

	int ret = -ENOENT;



	while (!__ublk_shmem_remove_ranges(ub, buf_index, &ret))

		cond_resched();

	return ret;

}