On Sun, 20 Mar 2022 07:12:33 +0100, Jakob Koschel <jakobkoschel@xxxxxxxxx> wrote: > > On 20. Mar 2022, at 03:57, Xiaomeng Tong <xiam0nd.tong@xxxxxxxxx> wrote: > > > > The bug is here: "if (dev == NULL)". > > > > The list iterator value will *always* be set and non-NULL by > > list_for_each_entry(), so it is incorrect to assume that the iterator > > value will be NULL if the list is empty or no element is found in list. > > > > Use a new value 'iter' as the list iterator, while use the old value > > 'req' as a dedicated pointer to point to the found element, which > > 1. can fix this bug, due to now 'req' is NULL only if it's not found. > > 2. do not need to change all the uses of 'req' after the loop. > > 3. can also limit the scope of the list iterator 'iter' *only inside* > > the traversal loop by simply declaring 'iter' inside the loop in the > > future, as usage of the iterator outside of the list_for_each_entry > > is considered harmful. https://lkml.org/lkml/2022/2/17/1032 > > > > Fixes: 4aabf6331f89c ("[PATCH] v4l: (951) Make saa7134-oss as a stand-alone module") > > Signed-off-by: Xiaomeng Tong <xiam0nd.tong@xxxxxxxxx> > > --- > > drivers/media/pci/saa7134/saa7134-alsa.c | 11 +++++++---- > > 1 file changed, 7 insertions(+), 4 deletions(-) > > > > diff --git a/drivers/media/pci/saa7134/saa7134-alsa.c b/drivers/media/pci/saa7134/saa7134-alsa.c > > index fb24d2ed3621..4955f7e7c5bf 100644 > > --- a/drivers/media/pci/saa7134/saa7134-alsa.c > > +++ b/drivers/media/pci/saa7134/saa7134-alsa.c > > @@ -1215,18 +1215,21 @@ static int alsa_device_exit(struct saa7134_dev *dev) > > static int saa7134_alsa_init(void) > > { > > struct saa7134_dev *dev = NULL; > > + struct saa7134_dev *iter; > > > > saa7134_dmasound_init = alsa_device_init; > > saa7134_dmasound_exit = alsa_device_exit; > > > > pr_info("saa7134 ALSA driver for DMA sound loaded\n"); > > > > - list_for_each_entry(dev, &saa7134_devlist, devlist) { > > - if (dev->pci->device == PCI_DEVICE_ID_PHILIPS_SAA7130) > > + list_for_each_entry(iter, &saa7134_devlist, devlist) { > > + dev = iter; > > + > > + if (iter->pci->device == PCI_DEVICE_ID_PHILIPS_SAA7130) > > pr_info("%s/alsa: %s doesn't support digital audio\n", > > - dev->name, saa7134_boards[dev->board].name); > > + iter->name, saa7134_boards[iter->board].name); > > else > > - alsa_device_init(dev); > > + alsa_device_init(iter); > > } > > > > if (dev == NULL) > > I could be wrong, but judging from the printed message "saa7134 ALSA: no saa7134 cards found" > and how the code is structured, I got the impression that the intention for this code was > to only execute if the list is empty. > > There is no break or anything so it's not looking for a specific element. > > It might make more sense to simply replace this check with: > if (list_empty(&saa7134_devlist)) Oh, yes. I think you are right. In addtion, the unneeded initializer for 'dev' can also be removed because the list iterator is always initialized. Thank you for the suggestion! -- Xiaomeng Tong
