Re: [PATCH] block: bios with an offset are always gappy

[Ming Lei]

On Thu, Apr 13, 2017 at 01:53:28PM +0200, Johannes Thumshirn wrote:
> On Thu, Apr 13, 2017 at 06:02:21PM +0800, Ming Lei wrote:
> > On Thu, Apr 13, 2017 at 10:06:29AM +0200, Johannes Thumshirn wrote:
> > > Doing a mkfs.btrfs on a (qemu emulated) PCIe NVMe causes a kernel panic
> > > in nvme_setup_prps() because the dma_len will drop below zero but the
> > > length not.
> > 
> > Looks I can't reproduce the issue in QEMU(32G nvme, either partitioned
> > or not, just use 'mkfs.btrfs /dev/nvme0n1p1'), could you share the exact
> > mkfs command line and size of your emulated NVMe?
> 
> the exact cmdline is mkfs.btrfs -f /dev/nvme0n1p1 (-f because there was a
> existing btrfs on the image). The image is 17179869184 (a.k.a 16G) bytes.
> 
> [...]
> 
> > Could you try the following patch to see if it fixes your issue?
> 
> It's back to the old, erratic behaviour, see log below.

Ok, could you apply the attached debug patch and collect the
ftrace log? (ftrace_dump_on_oops need to be passed to kernel cmd line).


Thanks,
Ming

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 26a5fd05fe88..a813a36d48d9 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -491,6 +491,8 @@ static bool nvme_setup_prps(struct nvme_dev *dev, struct request *req)
 			break;
 		if (dma_len > 0)
 			continue;
+		if (dma_len < 0)
+			blk_dump_rq(req, "nvme dma sg gap");
 		BUG_ON(dma_len < 0);
 		sg = sg_next(sg);
 		dma_addr = sg_dma_address(sg);
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 8e521194f6fc..f3b001e401d2 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -811,5 +811,29 @@ static inline int bio_integrity_add_page(struct bio *bio, struct page *page,
 
 #endif /* CONFIG_BLK_DEV_INTEGRITY */
 
+static inline void blk_dump_bio(struct bio *bio, const char *msg)
+{
+	struct bvec_iter iter;
+	struct bio_vec bvec;
+	int i = 0;
+	unsigned sectors = 0;
+
+	trace_printk("%s-%p: %hx/%hx %u %llu %u\n",
+                       msg, bio,
+                       bio->bi_flags, bio->bi_opf,
+                       bio->bi_phys_segments,
+                       (unsigned long long)bio->bi_iter.bi_sector,
+                       bio->bi_iter.bi_size);
+	bio_for_each_segment(bvec, bio, iter) {
+		sectors += bvec.bv_len >> 9;
+		trace_printk("\t %d: %lu %u %u(%u)\n", i++,
+				(unsigned long)page_to_pfn(bvec.bv_page),
+				bvec.bv_offset,
+				bvec.bv_len, bvec.bv_len >> 12);
+	}
+	trace_printk("\t total sectors %u\n", sectors);
+}
+
+
 #endif /* CONFIG_BLOCK */
 #endif /* __LINUX_BIO_H */
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 7548f332121a..b75d6fe5a1b9 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1698,6 +1698,22 @@ static inline bool req_gap_front_merge(struct request *req, struct bio *bio)
 	return bio_will_gap(req->q, bio, req->bio);
 }
 
+static inline void blk_dump_rq(const struct request *req, const char *msg)
+{
+	struct bio *bio;
+	int i = 0;
+
+	trace_printk("%s: dump bvec for %p(f:%x, seg: %d)\n",
+			msg, req, req->cmd_flags,
+			req->nr_phys_segments);
+
+	__rq_for_each_bio(bio, req) {
+		char num[16];
+		snprintf(num, 16, "%d", i++);
+		blk_dump_bio(bio, num);
+	}
+}
+
 int kblockd_schedule_work(struct work_struct *work);
 int kblockd_schedule_work_on(int cpu, struct work_struct *work);
 int kblockd_schedule_delayed_work(struct delayed_work *dwork, unsigned long delay);