At Tue, 7 Jan 2014 21:59:31 +0900, Ryusuke Konishi wrote: > > The sheepdog driver fails with io errors when write access is > requested for a snapshot vdi. The failure happens in create_branch > function: > > tgtd: read_write_object(684) No object found (oid: 8000000 > 000000000, old_oid: 0) > tgtd: create_branch(1160) reloading new inode object failed > tgtd: bs_sheepdog_request(1197) creating writable VDI from > snapshot failed > > sd 12:0:0:1: [sdb] Unhandled sense code > sd 12:0:0:1: [sdb] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE > sd 12:0:0:1: [sdb] Sense Key : Medium Error [current] > sd 12:0:0:1: [sdb] Add. Sense: Unrecovered read error > sd 12:0:0:1: [sdb] CDB: Write(10): 2a 00 00 00 20 a8 00 00 08 00 > Buffer I/O error on device sdb1, logical block 1041 > lost page write due to I/O error on sdb1 > > This turned out to be caused by a race condition among multiple write > requests. When bs_sheepdog_request() receives a write request for the > snapshot vdi, it tries to change the snapshot to a writable vdi with > the create_branch function. However, the current implementation of > create_branch() cannot handle concurrent requests exclusively nor > protected from regular io routine (sd_io). > > This fixes the above io-error issue by serializing create_branch() > with a pthread reader/writer lock, and also fixes the race condition > between create_branch() and sd_io() with the lock. > > Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxxxxxx> > Cc: Hitoshi Mitake <mitake.hitoshi@xxxxxxxxxxxxx> > --- > usr/bs_sheepdog.c | 22 +++++++++++++++++----- > 1 file changed, 17 insertions(+), 5 deletions(-) Ooops, thanks a lot for your fix. It must be a very hard debug and sorry for annoying! Reviewed-by: Hitoshi Mitake <mitake.hitoshi@xxxxxxxxxxxxx> Thanks, Hitoshi -- To unsubscribe from this list: send the line "unsubscribe stgt" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
