On Mon, 31 Mar 2014, Hannes Reinecke wrote: > >> Ah. Correct. But that's due to the first patch being incorrect. > >> Cf my response to the original first patch. > > > > See my response to your response. :-) > > > Okay, So I probably should refrain from issueing a response to > your response to my response lest infinite recursion happens :-) Indeed. > >>> What should happen if some other pathway manages to call > >>> scsi_try_to_abort_cmd() while scmd->abort_work is still > >>> sitting on the work queue? The command would be aborted > >>> and the flag would be cleared, but the queued work would > >>> remain. Can this ever happen? > >>> > >> Not that I could see. > >> A command abort is only ever triggered by the request timeout from > >> the block layer. And the timer is _not_ rearmed once the timeout > >> function (here: scsi_times_out()) is called. > >> Hence I fail to see how it can be called concurrently. > > > > scsi_try_to_abort_cmd() is also called (via a different pathway) when a > > command sent by the error handler itself times out. I haven't traced > > through all the different paths to make sure none of them can run > > concurrently. But I'm willing to take your word for it. > > > Yes, but that's not calling scsi_abort_command(), but rather invokes > scsi_abort_eh_cmnd(). Sure. But either way, we end up in scsi_try_to_abort_cmd(), which calls the LLDD's abort handler. Thus leading to the possibility of aborting the same command more than once. > >> The original idea was this: > >> > >> SCSI_EH_ABORT_SCHEDULED is sticky _per command_. > >> Point is, any command abort is only ever send for a timed-out > >> command. And the main problem for a timed-out command is that we > >> simply _do not_ know what happened for that command. So _if_ a > >> command timed out, _and_ we've send an abort, _and_ the command > >> times out _again_ we'll be running into an endless loop between > >> timeout and aborting, and never returning the command at all. > >> > >> So to prevent this we should set a marker on that command telling it > >> to _not_ try to abort the command again. > > > > I disagree. We _have_ to abort the command again -- how else can we > > stop a running command? To prevent the loop you described, we should > > avoid _retrying_ the command after it is aborted the second time. > > > The actual question is whether it's worth aborting the same command > a second time. > In principle any reset (like LUN reset etc) should clear the > command, too. > And the EH abort functionality is geared around this. > If, for some reason, the transport layer / device driver > requires a command abort to be send then sure, we need > to accommodate for that. As James mentioned, with USB a reset does not abort a running command. Instead it waits for the command to finish. (However, this could be changed in usb-storage, if required.) > As said, yes, in principle you are right. We should be aborting the > command a second time, _and then_ starting the escalation. > > So if the above reasoning is okay then this patch should be doing > the trick: > > diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c > index 771c16b..0e72374 100644 > --- a/drivers/scsi/scsi_error.c > +++ b/drivers/scsi/scsi_error.c > @@ -189,6 +189,7 @@ scsi_abort_command(struct scsi_cmnd *scmd) > /* > * Retry after abort failed, escalate to next level. > */ > + scmd->eh_eflags &= ~SCSI_EH_ABORT_SCHEDULED; > SCSI_LOG_ERROR_RECOVERY(3, > scmd_printk(KERN_INFO, scmd, > "scmd %p previous abort > failed\n", scmd)); > > (Beware of line > breaks) > > Can you test with it? I don't understand. This doesn't solve the fundamental problem (namely that you escalate before aborting a running command). All it does is clear the SCSI_EH_ABORT_SCHEDULED flag before escalating. What's needed is something like a 2-bit abort counter. scsi_try_to_abort_cmd() should increment the counter each time it runs, and if scmd_eh_abort_handler() sees that the counter is too high, it should avoid its retry pathway. _Then_ you can move on to something more drastic. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
