[PATCH] ublk: reduce stack usage in __ublk_shmem_remove_ranges

[PATCH] ublk: reduce stack usage in __ublk_shmem_remove_ranges

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

The array in __ublk_shmem_remove_ranges() is one kilobyte long,
which is really too much for an on-stack allocation, as can be
seen with a frame warning limit of 1.25kb that otherwise produces
a clean build on my test system:

drivers/block/ublk_drv.c: In function '__ublk_shmem_remove_ranges':
drivers/block/ublk_drv.c:5573:1: error: the frame size of 1392 bytes is larger than 1280 bytes [-Werror=frame-larger-than=]

Maybe half the size is good enough here, so try 32 entries.
If 64 entries are really required, the array could be dynamically
allocated, but that would risk an allocation failure.

Fixes: 309e02dccf64 ("ublk: avoid unpinning pages under maple tree spinlock")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
I have really no idea if the 64 number was significant or just chosen
to fit within usual stack frames.
---
 drivers/block/ublk_drv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 66eb55e7162e..6fe85aba32ce 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -5531,7 +5531,7 @@ static void ublk_unpin_range_pages(unsigned long base_pfn,
  *
  * Returns true if the tree walk completed, false if more ranges remain.
  */
-#define UBLK_REMOVE_BATCH	64
+#define UBLK_REMOVE_BATCH	32
 
 struct ublk_unpin_range {
 	unsigned long base_pfn;
-- 
2.53.0

Re: [PATCH] ublk: reduce stack usage in __ublk_shmem_remove_ranges

[Ming Lei]

On Tue, Sep 15, 2026 at 3:01 PM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> The array in __ublk_shmem_remove_ranges() is one kilobyte long,
> which is really too much for an on-stack allocation, as can be
> seen with a frame warning limit of 1.25kb that otherwise produces
> a clean build on my test system:
>
> drivers/block/ublk_drv.c: In function '__ublk_shmem_remove_ranges':
> drivers/block/ublk_drv.c:5573:1: error: the frame size of 1392 bytes is larger than 1280 bytes [-Werror=frame-larger-than=]
>
> Maybe half the size is good enough here, so try 32 entries.
> If 64 entries are really required, the array could be dynamically
> allocated, but that would risk an allocation failure.
>
> Fixes: 309e02dccf64 ("ublk: avoid unpinning pages under maple tree spinlock")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> I have really no idea if the 64 number was significant or just chosen
> to fit within usual stack frames.
> ---
>  drivers/block/ublk_drv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index 66eb55e7162e..6fe85aba32ce 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -5531,7 +5531,7 @@ static void ublk_unpin_range_pages(unsigned long base_pfn,
>   *
>   * Returns true if the tree walk completed, false if more ranges remain.
>   */
> -#define UBLK_REMOVE_BATCH      64
> +#define UBLK_REMOVE_BATCH      32

Reviewed-by: Ming Lei <tom.leiming@gmail.com>

Thanks,
Ming Lei