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Tue, 27 Nov 2018 13:57:30 +0000 Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by aserv0021.oracle.com (8.14.4/8.14.4) with ESMTP id wARDvTJx025095 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 27 Nov 2018 13:57:29 GMT Received: from abhmp0012.oracle.com (abhmp0012.oracle.com [141.146.116.18]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id wARDvS17028719; Tue, 27 Nov 2018 13:57:28 GMT Received: from dhcp-burlington7-2nd-B-east-10-152-55-162.usdhcp.oraclecorp.com (/10.152.32.65) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 27 Nov 2018 05:57:28 -0800 Subject: Re: [PATCH] xen/x86: add diagnostic printout to xen_mc_flush() in case of error To: Juergen Gross , linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, x86@kernel.org Cc: sstabellini@kernel.org, hpa@zytor.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de References: <20181123162451.3351-1-jgross@suse.com> <0727da38-bfe8-f484-6b06-7205c1d953c1@oracle.com> <04dc8206-d7ad-9438-2f68-c25bf5a10b96@suse.com> From: Boris Ostrovsky Openpgp: preference=signencrypt Autocrypt: addr=boris.ostrovsky@oracle.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 MIME-Version: 1.0 In-Reply-To: <04dc8206-d7ad-9438-2f68-c25bf5a10b96@suse.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9089 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1811270120 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/27/18 2:46 AM, Juergen Gross wrote: > On 26/11/2018 21:11, Boris Ostrovsky wrote: >> On 11/23/18 11:24 AM, Juergen Gross wrote: >>> Failure of an element of a Xen multicall is signalled via a WARN() >>> only unless the kernel is compiled with MC_DEBUG. It is impossible to >> s/unless/if >> >> >>> know which element failed and why it did so. >>> >>> Change that by printing the related information even without MC_DEBUG, >>> even if maybe in some limited form (e.g. without information which >>> caller produced the failing element). >>> >>> Move the printing out of the switch statement in order to have the >>> same information for a single call. >>> >>> Signed-off-by: Juergen Gross >>> --- >>> arch/x86/xen/multicalls.c | 35 ++++++++++++++++++++--------------- >>> 1 file changed, 20 insertions(+), 15 deletions(-) >>> >>> diff --git a/arch/x86/xen/multicalls.c b/arch/x86/xen/multicalls.c >>> index 2bce7958ce8b..0766a08bdf45 100644 >>> --- a/arch/x86/xen/multicalls.c >>> +++ b/arch/x86/xen/multicalls.c >>> @@ -69,6 +69,11 @@ void xen_mc_flush(void) >>> >>> trace_xen_mc_flush(b->mcidx, b->argidx, b->cbidx); >>> >>> +#if MC_DEBUG >>> + memcpy(b->debug, b->entries, >>> + b->mcidx * sizeof(struct multicall_entry)); >>> +#endif >>> + >>> switch (b->mcidx) { >>> case 0: >>> /* no-op */ >>> @@ -87,32 +92,34 @@ void xen_mc_flush(void) >>> break; >>> >>> default: >>> -#if MC_DEBUG >>> - memcpy(b->debug, b->entries, >>> - b->mcidx * sizeof(struct multicall_entry)); >>> -#endif >>> - >>> if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0) >>> BUG(); >>> for (i = 0; i < b->mcidx; i++) >>> if (b->entries[i].result < 0) >>> ret++; >>> + } >>> >>> + if (WARN_ON(ret)) { >>> + pr_err("%d of %d multicall(s) failed: cpu %d\n", >>> + ret, b->mcidx, smp_processor_id()); >>> + for (i = 0; i < b->mcidx; i++) { >>> + if (b->entries[i].result < 0) { >>> #if MC_DEBUG >>> - if (ret) { >>> - printk(KERN_ERR "%d multicall(s) failed: cpu %d\n", >>> - ret, smp_processor_id()); >>> - dump_stack(); >>> - for (i = 0; i < b->mcidx; i++) { >>> - printk(KERN_DEBUG " call %2d/%d: op=%lu arg=[%lx] result=%ld\t%pF\n", >>> - i+1, b->mcidx, >>> + pr_err(" call %2d: op=%lu arg=[%lx] result=%ld\t%pF\n", >>> + i + 1, >>> b->debug[i].op, >>> b->debug[i].args[0], >>> b->entries[i].result, >>> b->caller[i]); >>> +#else >>> + pr_err(" call %2d: op=%lu arg=[%lx] result=%ld\n", >>> + i + 1, >>> + b->entries[i].op, >>> + b->entries[i].args[0], >>> + b->entries[i].result); >>> +#endif >> Doesn't (non-debug) hypervisor corrupt op and args? > No. Only debug hypervisor does so. > > See my patch (and rather lengthy discussion) on xen-devel: > > https://lists.xen.org/archives/html/xen-devel/2018-11/msg02714.html Yes, I saw that later, after I responded to the patch. > >> (Also, we don't really need to print anything when b->entries[i].result >> == 0) > Right. Did you miss the: I did. Reviewed-by: Boris Ostrovsky (with commit message fixed) > > + if (b->entries[i].result < 0) { > > above? > > > Juergen