On 10/06/2015 12:19 PM, James Bottomley wrote: > On Tue, 2015-10-06 at 12:08 -0700, Lee Duncan wrote: >> Update the SCSI hosts module to use idr to manage >> its host_no index instead of an ATOMIC integer. This >> also allows using idr_find() to look up the SCSI >> host structure given the host number. >> >> This means that the SCSI host number will now >> be reclaimable. >> >> Signed-off-by: Lee Duncan <lduncan@xxxxxxxx> >> Reviewed-by: Hannes Reinecke <hare@xxxxxxxx> >> --- >> drivers/scsi/hosts.c | 61 ++++++++++++++++++++++++++-------------------------- >> 1 file changed, 31 insertions(+), 30 deletions(- >> >> diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c >> index 8bb173e01084..afe7bd962ddb 100644 >> --- a/drivers/scsi/hosts.c >> +++ b/drivers/scsi/hosts.c > [...] >> + spin_lock(&host_index_lock); >> + shost = idr_find(&host_index_idr, hostnum); >> + spin_unlock(&host_index_lock); >> + >> + return shost ? scsi_host_get(shost) : NULL; > > So the thing I don't like here is that there's a race between > scsi_host_get() and the final put. What could happen is that idr_find() > returns the host just before but scsi_host_dev_release() is executed > before the return. In that instance, we'll reference freed memory in > scsi_host_get() ... probably completely harmlessly, but it will show up > occasionally on some of the traces ... particularly the ones doing a > fuzz/stress test around host create/destroy. > > James Good point. The scenario you mention may be a corner case, but I also don't like it. I cannot see another good way to synchronize lookup and removal other than adding a new lock, which would be dumb. I will submit my "host number" patch again, without the change to scsi_host_lookup(). -- Lee Duncan -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
