On Tue, 07 Jan 2014 22:23:00 +0900 Hitoshi Mitake <mitake.hitoshi@xxxxxxxxx> wrote: > 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> Applied, thanks a lot, guys. -- 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
