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yaml --- r: 147052 b: refs/heads/master c: 53674ac h: refs/heads/master v: v3
git-mirror · May 19, 2009 · 3a36ecb · 3a36ecb
1 parent 2aa349e
commit 3a36ecb
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diff --git a/[refs] b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: a411f4bbb89f1f08687b344064d6775bce1e4658
+refs/heads/master: 53674ac5a997a8eedbb2dfdc308b895170746c8b
diff --git a/trunk/block/blk-core.c b/trunk/block/blk-core.c
@@ -910,6 +910,15 @@ EXPORT_SYMBOL(blk_get_request);
  * need bouncing, by calling the appropriate masked or flagged allocator,
  * suitable for the target device. Otherwise the call to blk_queue_bounce will
  * BUG.
+ *
+ * WARNING: When allocating/cloning a bio-chain, careful consideration should be
+ * given to how you allocate bios. In particular, you cannot use __GFP_WAIT for
+ * anything but the first bio in the chain. Otherwise you risk waiting for IO
+ * completion of a bio that hasn't been submitted yet, thus resulting in a
+ * deadlock. Alternatively bios should be allocated using bio_kmalloc() instead
+ * of bio_alloc(), as that avoids the mempool deadlock.
+ * If possible a big IO should be split into smaller parts when allocation
+ * fails. Partial allocation should not be an error, or you risk a live-lock.
  */
 struct request *blk_make_request(struct request_queue *q, struct bio *bio,
 				 gfp_t gfp_mask)