ounter is incremented when building a BIO in sync_request() and is decremented when finish a BIO in end_sync_write(). If building a BIO fails for some reasons in sync_request(), the "remaining" should be decremented if it has already been incremented. I found a case where this decrement is forgotten. This causes a md_do_sync() deadlock because md_do_sync() waits for md_done_sync() called by end_sync_write(), but end_sync_write() never calls md_done_sync() because of the "remaining" counter mismatch. For example, this problem would be reproduced in the following case: Personalities : [raid10] md0 : active raid10 sdf1[4] sde1[5](F) sdd1[2] sdc1[1] sdb1[6](F) 3919616 blocks 64K chunks 2 near-copies [4/2] [_UU_] [>....................] recovery = 2.2% (45376/1959808) finish=0.7min speed=45376K/sec This case, sdf1 is recovering, sdb1 and sde1 are disabled. An additional error with detaching sdd will cause a deadlock. md0 : active raid10 sdf1[4] sde1[5](F) sdd1[6](F) sdc1[1] sdb1[7](F) 3919616 blocks 64K chunks 2 near-copies [4/1] [_U__] [=>...................] recovery = 5.0% (99520/1959808) finish=5.9min speed=5237K/sec 2739 ? S< 0:17 [md0_raid10] 28608 ? D< 0:00 [md0_resync] 28629 pts/1 Ss 0:00 bash 28830 pts/1 R+ 0:00 ps ax 31819 ? D< 0:00 [kjournald] The resync thread keeps working, but actually it is deadlocked. Patch: By this patch, the remaining counter will be decremented if needed. Signed-off-by: Neil Brown Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Š<8€˜8x