[PATCH] block: bio: ensure newly added bio flags don't override BVEC_POOL_IDX

* [PATCH] block: bio: ensure newly added bio flags don't override BVEC_POOL_IDX
@ 2019-04-03  9:15 Johannes Thumshirn
  2019-04-03  9:57 ` Ming Lei
                   ` (4 more replies)
  0 siblings, 5 replies; 6+ messages in thread
From: Johannes Thumshirn @ 2019-04-03  9:15 UTC (permalink / raw)
  To: Jens Axboe
  Cc: Linux Block Layer Mailinglist, Linux FSDEVEL Mailinglist,
	Christoph Hellwig, Hannes Reinecke, Johannes Thumshirn

With the introduction of BIO_NO_PAGE_REF we've used up all available bits
in bio::bi_flags.

Convert the defines of the flags to an enum and add a BUILD_BUG_ON() call
to make sure no-one adds a new one and thus overrides the BVEC_POOL_IDX
causing crashes.

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>

---
This used to be part of my bio patchset but as it's a) not clear why we
end up calling bio_put() on the on-stack bio and b) the needed prep patch
for the fix introduces a regression, I've decided to sent this patch out
as it's valid on it's own.

I dropped Hannes' and Christoph's R-b though, as the context changed.
---
 block/bio.c               |  3 +++
 include/linux/blk_types.h | 29 ++++++++++++++++-------------
 2 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 8d516d508ae3..c2592c5d70b9 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -2218,6 +2218,9 @@ static int __init init_bio(void)
 	bio_slab_nr = 0;
 	bio_slabs = kcalloc(bio_slab_max, sizeof(struct bio_slab),
 			    GFP_KERNEL);
+
+	BUILD_BUG_ON(BIO_FLAG_LAST > BVEC_POOL_OFFSET);
+
 	if (!bio_slabs)
 		panic("bio: can't allocate bios\n");
 
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 791fee35df88..be418275763c 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -215,21 +215,24 @@ struct bio {
 /*
  * bio flags
  */
-#define BIO_NO_PAGE_REF	0	/* don't put release vec pages */
-#define BIO_SEG_VALID	1	/* bi_phys_segments valid */
-#define BIO_CLONED	2	/* doesn't own data */
-#define BIO_BOUNCED	3	/* bio is a bounce bio */
-#define BIO_USER_MAPPED 4	/* contains user pages */
-#define BIO_NULL_MAPPED 5	/* contains invalid user pages */
-#define BIO_QUIET	6	/* Make BIO Quiet */
-#define BIO_CHAIN	7	/* chained bio, ->bi_remaining in effect */
-#define BIO_REFFED	8	/* bio has elevated ->bi_cnt */
-#define BIO_THROTTLED	9	/* This bio has already been subjected to
+enum {
+	BIO_NO_PAGE_REF,	/* don't put release vec pages */
+	BIO_SEG_VALID,		/* bi_phys_segments valid */
+	BIO_CLONED,		/* doesn't own data */
+	BIO_BOUNCED,		/* bio is a bounce bio */
+	BIO_USER_MAPPED,	/* contains user pages */
+	BIO_NULL_MAPPED,	/* contains invalid user pages */
+	BIO_QUIET,		/* Make BIO Quiet */
+	BIO_CHAIN,		/* chained bio, ->bi_remaining in effect */
+	BIO_REFFED,		/* bio has elevated ->bi_cnt */
+	BIO_THROTTLED,		/* This bio has already been subjected to
 				 * throttling rules. Don't do it again. */
-#define BIO_TRACE_COMPLETION 10	/* bio_endio() should trace the final completion
+	BIO_TRACE_COMPLETION,	/* bio_endio() should trace the final completion
 				 * of this bio. */
-#define BIO_QUEUE_ENTERED 11	/* can use blk_queue_enter_live() */
-#define BIO_TRACKED 12		/* set if bio goes through the rq_qos path */
+	BIO_QUEUE_ENTERED,	/* can use blk_queue_enter_live() */
+	BIO_TRACKED,		/* set if bio goes through the rq_qos path */
+	BIO_FLAG_LAST
+};
 
 /* See BVEC_POOL_OFFSET below before adding new flags */
 
-- 
2.16.4


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