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Tue, 09 Jun 2026 09:01:32 -0700 (PDT) Date: Tue, 9 Jun 2026 17:02:32 +0100 From: Nuno =?utf-8?B?U8Oh?= To: Paul Cercueil Cc: Greg Kroah-Hartman , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, Nuno =?utf-8?B?U8Oh?= , stable@vger.kernel.org Subject: Re: [PATCH] usb: gadget: f_fs: Fix DMA fence leak Message-ID: References: <20260609152905.729328-1-paul@crapouillou.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260609152905.729328-1-paul@crapouillou.net> On Tue, Jun 09, 2026 at 05:29:05PM +0200, Paul Cercueil wrote: > In ffs_dmabuf_transfer(), a ffs_dma_fence object is kmalloc'd, with the > underlying dma_fence later initialized by dma_fence_init(), which sets > its kref counter to 1. Then, dma_resv_add_fence() gets a second > reference, and a pointer to the ffs_dma_fence is passed as the > usb_request's "context" field. > > The dma-resv mechanism will manage the second reference, but the first > reference is never properly released; the ffs_dmabuf_cleanup() function > decreases the reference count, but only to balance with the reference > grab in ffs_dmabuf_signal_done(). > > The code will then slowly leak memory as more ffs_dma_fence objects are > created without being ever freed. > > Address this issue by transferring ownership of the fence to the DMA > reservation object, by calling dma_fence_put() right after > dma_resv_add_fence(). The ffs_dma_fence then gets properly discarded > after being signalled. > > Fixes: 7b07a2a7ca02 ("usb: gadget: functionfs: Add DMABUF import interface") > Cc: stable@vger.kernel.org > Signed-off-by: Paul Cercueil > --- Tested-by: Nuno Sá Reviewed-by: Nuno Sá > drivers/usb/gadget/function/f_fs.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c > index 75912ce6ab55..7cc446502980 100644 > --- a/drivers/usb/gadget/function/f_fs.c > +++ b/drivers/usb/gadget/function/f_fs.c > @@ -1704,6 +1704,7 @@ static int ffs_dmabuf_transfer(struct file *file, > resv_dir = epfile->in ? DMA_RESV_USAGE_READ : DMA_RESV_USAGE_WRITE; > > dma_resv_add_fence(dmabuf->resv, &fence->base, resv_dir); > + dma_fence_put(&fence->base); > dma_resv_unlock(dmabuf->resv); > > /* Now that the dma_fence is in place, queue the transfer. */ > -- > 2.53.0 >