陈华才 江苏中科梦兰电子科技有限公司/自主安全事业部/软件部 江苏常熟虞山镇梦兰村
------------------ Original ------------------ From: "Thomas Gleixner"tglx@linutronix.de; Date: Wed, Jan 16, 2019 05:26 PM To: "陈华才"chenhc@lemote.com; Cc: "linux-kernel"linux-kernel@vger.kernel.org; "Fuxin Zhang"zhangfx@lemote.com; "wuzhangjin"wuzhangjin@gmail.com; "stable"stable@vger.kernel.org; "Christoph Hellwig"hch@lst.de; "Michael Hernandez"michael.hernandez@cavium.com; Subject: Re: [PATCH] genirq/affinity: Assign default affinity to pre/post vectors
Chen,
On Wed, 16 Jan 2019, 陈华才 wrote:
please do not top-post and use line breaks around 78 char.
I'm not removing all return NULL of irq_create_affinity_masks(), so the ......
Moved content to the place where it belongs so the context is preserved.
------------------ Original ------------------ From: "Thomas Gleixner"tglx@linutronix.de; Date: Wed, Jan 16, 2019 03:10 AM To: "Huacai Chen"chenhc@lemote.com; Cc: "linux-kernel"linux-kernel@vger.kernel.org; "Fuxin Zhang"zhangfx@lemote.com; "wuzhangjin"wuzhangjin@gmail.com; "stable"stable@vger.kernel.org; "Christoph Hellwig"hch@lst.de; "Michael Hernandez"michael.hernandez@cavium.com; Subject: Re: [PATCH] genirq/affinity: Assign default affinity to pre/post vectors
And please configure your e-mail client to NOT copy the full headers into the reply.
On Mon, 31 Dec 2018, Huacai Chen wrote:
Generally, irq_create_affinity_masks() assign default affinity to pre/ post vectors correctly. However, it ignore the case that there are only pre/post vectors (when nvecs == affd->pre_vectors + affd->post_vectors) and return NULL. This case usually happens when nvecs = 1 (e.g. in nvme driver when MSI-X is unavailable and fallback to MSI) and will trigger the warning in pci_irq_get_affinity(). This patch fix the corner case.
Errm. This is just wrong. When this function returns NULL, then it has failed and the caller or any subsequent code is not supposed to use the result.
The function can return NULL for other reasons, e.g. when the memory allocation failed. How are you going to duct tape that one?
I'm not removing all return NULL of irq_create_affinity_masks(), so the memory allocation failure still return NULL. I just handle the case that there are not enough irq vectors. E.g. in nvme driver, the caller may call irq_create_affinity_masks() with nvecs=1,pre_vectors=1,post_vectors=0. In this case, the only one vector's default affinity assigning is skipped.
I did not say that you removed all NULL returns. I said that this function can return NULL for other reasons and then the same situation will happen.
If the masks pointer returned is NULL then the calling code or any subsequent usage needs to handle it properly. Yes, I understand that this change makes the warning go away for that particular case, but that's not making it any more correct.
Hi, Thomas,
I don't think "nvecs == affd->pre_vectors + affd->post_vectors" is an ERROR, so it should be different with "return NULL for other reasons" to the caller. If the caller fallback from MSI-X to MSI, it is probably "nvecs=1,pre_vectors=1, post_vectors=0". The caller can work perfectly, if pre/post vectors are filled with the default affinity.
Thanks,
tglx