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Tue, 25 Mar 2025 06:40:06 -0700 (PDT) From: Petr Tesarik To: Greg Kroah-Hartman , linux-usb@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Petr Tesarik Subject: [PATCH v2] usb: core: warn if a GFP zone flag is passed to hcd_buffer_alloc() Date: Tue, 25 Mar 2025 14:40:00 +0100 Message-ID: <20250325134000.575794-1-ptesarik@suse.com> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250320154733.392410-1-ptesarik@suse.com> References: <20250320154733.392410-1-ptesarik@suse.com> Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Remove a misleading comment and issue a warning if a zone modifier is specified when allocating a hcd buffer. There is no valid use case for a GFP zone modifier in hcd_buffer_alloc(): - PIO mode can use any kernel-addressable memory - dma_alloc_coherent() ignores memory zone bits This function is called by usb_alloc_coherent() and indirectly by usb_submit_urb(). Despite the comment, no in-tree users currently pass GFP_DMA. Signed-off-by: Petr Tesarik --- drivers/usb/core/buffer.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/drivers/usb/core/buffer.c b/drivers/usb/core/buffer.c index 87230869e1fa..10844cd42e66 100644 --- a/drivers/usb/core/buffer.c +++ b/drivers/usb/core/buffer.c @@ -108,10 +108,6 @@ void hcd_buffer_destroy(struct usb_hcd *hcd) } -/* sometimes alloc/free could use kmalloc with GFP_DMA, for - * better sharing and to leverage mm/slab.c intelligence. - */ - void *hcd_buffer_alloc( struct usb_bus *bus, size_t size, @@ -128,6 +124,12 @@ void *hcd_buffer_alloc( if (hcd->localmem_pool) return gen_pool_dma_alloc(hcd->localmem_pool, size, dma); + /* + * Zone modifiers are ignored by DMA API, and PIO should always use + * GFP_KERNEL. + */ + WARN_ON_ONCE(mem_flags & GFP_ZONEMASK); + /* some USB hosts just use PIO */ if (!hcd_uses_dma(hcd)) { *dma = ~(dma_addr_t) 0;