On 05/20/14 09:32, Bart Van Assche wrote: > On 05/19/14 18:43, Bart Van Assche wrote: >> On 05/19/14 18:09, Paolo Bonzini wrote: >>> Il 19/05/2014 17:08, Bart Van Assche ha scritto: >>>> On 05/19/14 16:08, Paolo Bonzini wrote: >>>>> 2) reentrancy: the softirq handler and scmd_eh_abort_handler can run >>>>> concurrently, and call scsi_finish_command without any lock protecting >>>>> the calls. You can then get memory corruption. >>>> >>>> I'm not sure what the recommended approach is to address this race. But >>>> it is possible to address this in the LLD. See e.g. the srp_claim_req() >>>> function in the SRP LLD and how it is invoked from the reply handler, >>>> the abort handler and the reset handlers in that LLD. >>> >>> That's not enough, unless I'm missing something. Say the request >>> handler claims the request and the abort handler doesn't: >>> >>> - the request handler calls scsi_done and ends up in scsi_finish_command. >>> >>> - the abort handler will return SUCCESS, and scmd_eh_abort_handler then >>> calls scsi_finish_command. >> >> It depends on how the SCSI abort handler gets invoked. If the SCSI abort >> handler gets invoked because a SCSI command timed out that means that >> the block layer has already detected a timeout and also that the >> REQ_ATOM_COMPLETE bit has already been set. In this scenario if a SCSI >> LLD invokes scsi_done() that causes blk_complete_request() to return >> without invoking __blk_complete_request() and hence without invoking >> scsi_softirq_done(). > > (replying to my own e-mail) > > Please note that scsi_eh_abort_cmds() neither checks nor sets the > REQ_ATOM_COMPLETE bit before it invokes hostt->eh_abort_handler(). Would > it make sense to modify that function such that it invokes > blk_abort_request() instead ? That last function atomically > test-and-sets the REQ_ATOM_COMPLETE bit before invoking the timeout handler.
(answering my own question) REQ_ATOM_COMPLETE is already set before scsi_eh_scmd_add() is called since that function is only invoked after the block layer has marked a request as "complete". The only callers of scsi_eh_scmd_add() are scsi_softirq_done(), scsi_times_out() and scmd_eh_abort_handler(). That last function is invoked (indirectly) by scsi_times_out(). Bart. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
