Jens Axboe wrote:
To shed some more light on this, I'd suggest changing that BUG_ON() to
some code that simply dumps each segment (each bvec in the iterator
list) from start to finish along with values of
request->nr_phys_segments and size info.
OK, something like this?
J
Subject: xen/blkfront: try to track down over-segment BUG_ON in blkfront
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
---
drivers/block/xen-blkfront.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)
===================================================================
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -240,7 +240,10 @@
ring_req->nr_segments = 0;
rq_for_each_segment(bvec, req, iter) {
- BUG_ON(ring_req->nr_segments == BLKIF_MAX_SEGMENTS_PER_REQUEST);
+ if (WARN_ON(ring_req->nr_segments >=
+ BLKIF_MAX_SEGMENTS_PER_REQUEST))
+ goto dump_req;
+
buffer_mfn = pfn_to_mfn(page_to_pfn(bvec->bv_page));
fsect = bvec->bv_offset >> 9;
lsect = fsect + (bvec->bv_len >> 9) - 1;
@@ -274,6 +277,25 @@
gnttab_free_grant_references(gref_head);
return 0;
+
+dump_req:
+ {
+ int i;
+
+ printk(KERN_DEBUG "too many segments for ring (%d): "
+ "req->nr_phys_segments = %d\n",
+ BLKIF_MAX_SEGMENTS_PER_REQUEST, req->nr_phys_segments);
+
+ i = 0;
+ rq_for_each_segment(bvec, req, iter) {
+ printk(KERN_DEBUG
+ " %d: bio page %p pfn %lx off %u len %u\n",
+ i++, bvec->bv_page, page_to_pfn(bvec->bv_page),
+ bvec->bv_offset, bvec->bv_len);
+ }
+ }
+
+ return 1;
}
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