On Tue, Nov 07, 2017 at 04:13:48PM +0000, Bart Van Assche wrote: > On Tue, 2017-11-07 at 23:21 +0800, Ming Lei wrote: > > cmd->cmnd can be allocated/freed dynamically in case of T10_PI_TYPE2_PROTECTION, > > so we can't access it in scsi_show_rq() if 'SCpnt->cmnd != scsi_req(rq)->cmd', > > because this request can be freed any time. > > That description is inaccurate. It is not allowed to free SCpnt->cmnd while > a command is being executed. But can you prevent this request being freed when reading this debugfs file? > > > diff --git a/drivers/scsi/scsi_debugfs.c b/drivers/scsi/scsi_debugfs.c > > index 5e9755008aed..7a50878446b4 100644 > > --- a/drivers/scsi/scsi_debugfs.c > > +++ b/drivers/scsi/scsi_debugfs.c > > @@ -9,7 +9,10 @@ void scsi_show_rq(struct seq_file *m, struct request *rq) > > int msecs = jiffies_to_msecs(jiffies - cmd->jiffies_at_alloc); > > char buf[80]; > > > > - __scsi_format_command(buf, sizeof(buf), cmd->cmnd, cmd->cmd_len); > > + if (cmd->cmnd == scsi_req(rq)->cmd) > > + __scsi_format_command(buf, sizeof(buf), cmd->cmnd, cmd->cmd_len); > > + else > > + strcpy(buf, "unknown"); > > seq_printf(m, ", .cmd=%s, .retries=%d, allocated %d.%03d s ago", buf, > > cmd->retries, msecs / 1000, msecs % 1000); > > } > > This change introduces a new bug, namely that "unknown" will appear in the > debugfs output if (cmd->cmnd != scsi_req(rq)->cmd). Have you considered to use Because there isn't reliable way to get the command safely, and I don't think it is a new bug. > the test (cmd->cmnd != NULL) instead? No, that is worse, because you may cause use-after-free if you read a freed buffer. -- Ming
