From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bart Van Assche Subject: Re: dangling pointers and/or reentrancy in scmd_eh_abort_handler? Date: Mon, 19 May 2014 18:43:50 +0200 Message-ID: <537A34C6.7090905@acm.org> References: <537A105B.4080504@redhat.com> <537A1E88.9080803@acm.org> <537A2CB8.9060302@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Return-path: Received: from andre.telenet-ops.be ([195.130.132.53]:51708 "EHLO andre.telenet-ops.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932516AbaESQnx (ORCPT ); Mon, 19 May 2014 12:43:53 -0400 In-Reply-To: <537A2CB8.9060302@redhat.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Paolo Bonzini , linux-scsi , Ulrich Obergfell 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(). Bart.