From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-144.mta1.migadu.com [95.215.58.144]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5C7A551A139 for ; Tue, 22 Sep 2026 10:37:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.144 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790073465; cv=none; b=r6vufSwF6y3QULfWjIRTaCQKxUApGTDMGJQmnipu8CsQOqz1apgSvJnN8068BAyNhAKsSy9zugChGOx7bx48NhVi6r6ZZc3JaSWAux/cPkdY+ktRCkwQ8hk8UbttMFmLfMzYkVT3NBu3kCBepsbkcCIvMdPkqvUGl3DTX5VYWSE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790073465; c=relaxed/simple; bh=hOQCikqeresRs28eGornj2bzQ3r41eUFX91G9l/2z3c=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=hRGJik1tXlZtoNU7nBb2wUrFQQaPV+HmsHjx1HXQ0jzHirXD5sLN2lsphvj9Cz2CGzKyDlVvzdaH7bMo4zMvfzUNN7g46P+gaV3e0JwNM/g0Wlk1/h2rCkdBvUa6fGyyimCP3z3fbxCvTbcEpL0YuSXxDQmhr6B79O8Cei2lCGk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=fiiOCG2z; arc=none smtp.client-ip=95.215.58.144 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="fiiOCG2z" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=hOQCikqeresRs28eGornj2bzQ3r41eUFX91G9l/2z3c=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1790073461; v=1; x=1790678261; b=fiiOCG2zAAOO8bqcgS3IUOm+YRG1lPxcca+I2CuxCosIPYoYoZPPwHZSiDB1Oem5FKo91Xtr +X3tqENu2EdQtv1NOrhST8amrihxE1nyfAbUVkZe+XXYr2Lo9/shj+AzoE8Ck5HH/FfbQigJNY8 HSK1bs+Q0PnSxqgVPMi5sC0s= X-Envelope-To: linux-kernel@vger.kernel.org Received: by mta11.migadu.com with ESMTPS id 7c9d515ba9949150; Tue, 22 Sep 2026 10:37:41 +0000 X-Mizu-Trace-ID: 7c9d515ba9949150 X-Migadu-Flow: FLOW_OUT Message-ID: Date: Tue, 22 Sep 2026 11:37:35 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] scsi: libsas: Fix SMP IO deadlock during HA resume To: yangxingui , yanaijie@huawei.com, jejb@linux.ibm.com, mkp@kernel.org Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, linuxarm@huawei.com, liuyonglong@huawei.com, kangfenglong@huawei.com References: <20260918070307.381207-1-yangxingui@huawei.com> <9a72eeb3-ca32-4241-9e21-74cf894a9bf1@linux.dev> <627a27fc-b025-4bc1-8601-b0fca0e1c4e1@linux.dev> Content-Language: en-US From: John Garry In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 9/22/26 04:10, yangxingui wrote: >>> >>> It is also a narrow trigger: a directly-attached ATA device resets its >>> phy via lldd_control_phy() (no SMP IO), so it needs an expander- >>> attached ATA device whose EH lands inside the drain of a runtime >>> resume - which is why the testing of 3dbbbf656b85, whose scenario was >>> the disk-wake race, did not catch it. >> >> uh, the expander-attached SATA disk scenario would be a very common >> scenario - do you test this always when developing this code? > Yes，we do have a full test suite, but it runs per machine topology. The > 3dbbbf656b85 validation ran on the direct-attach configuration, since > the HA resume race it was fixing was originally reported there. The > expander topology was covered in the next test round, and this > deadlock showed up as soon as we switched to it: on that topology > every ATA port resume goes through the EH reset (that is how > ata_sas_port_resume() is implemented), so the SMP IO against the > ongoing runtime resume happens on essentially every cycle. > So it seems that the expander-attached scenario was not tested for that comment mentioned. You need to test directly-attached and expander-attached config for any relevant patchset. Otherwise we have this scenario that alternate configs are continually broken. >>> >>> Given that, should Fixes: point at 3dbbbf656b85 instead? I kept >>> 0da7ca4c4fd9 as that is where the pm_runtime_get_sync() being fixed >>> comes from, but the deadlock itself only exists where 3dbbbf656b85 >>> is. >>> >> I am just wondering why this needs to be fixed so many times... > Aha - each respin addressed a review finding on the PM > reference handling, not a re-fix of the deadlock. The core fix is > unchanged since v1. >> >> >> diff --git a/drivers/scsi/libsas/sas_expander.c b/drivers/scsi/libsas/ >> sas_expander.c >> index 811c9eb4fef1..5a8cdd3682fe 100644 >> --- a/drivers/scsi/libsas/sas_expander.c >> +++ b/drivers/scsi/libsas/sas_expander.c >> @@ -61,8 +61,22 @@ static int smp_execute_task_sg(struct domain_device >> *dev, >>       struct sas_internal *i = >>           to_sas_internal(dev->port->ha->shost->transportt); >>       struct sas_ha_struct *ha = dev->port->ha; >> - >> -    pm_runtime_get_sync(ha->dev); >> +    bool ha_resuming = test_bit(SAS_HA_RESUMING, &ha->state); >> + >> +    /* >> +     * While the host is resuming, ha->dev may be RPM_RESUMING and >> +     * the resume blocked in sas_drain_work() waiting for this very >> +     * SMP IO, so waiting for the host to resume here would deadlock. >> +     * Hold the reference without resuming, the hardware is already >> +     * initialized by the LLDD before sas_resume_ha() runs. >> +     */ >> +    if (ha_resuming) { >> +        pm_runtime_get_noresume(ha->dev); >> +    } else { >> +        res = pm_runtime_resume_and_get(ha->dev); >> >> why change from pm_runtime_get_sync() to pm_runtime_resume_and_get()? > > That addresses the pre-existing issue which Sashiko flagged: Then that would be a separate change. > the > return value of pm_runtime_get_sync() was ignored, so on a failed > resume the code would blindly proceed to submit the SMP task anyway. > Simply checking the return of pm_runtime_get_sync() would be awkward: > it keeps the usage counter incremented even on failure, so the error > path would also need a manual pm_runtime_put_noidle() to balance it. > pm_runtime_resume_and_get() rolls the counter back internally and > returns 0 or an errno, so the check is just "if (res) return res;" > >> >> +        if (res) >> +            return res; >> +    } >> >> So when is it required to really do pm_runtime_resume_and_get() (and >> not pm_runtime_get_noresume())? I mean, when is this called such that >> we need to resume the ha->dev? > Outside the resume window, the caller that needs the resume is BSG > userspace SMP requests (sas_smp_handler): ses/expander tools query > the topology at any time and nothing else holds the host awake, so > the host may have autosuspended; the resume also re-registers the > devices (the PHYE -> dev_found path runs inside the resume), so the > IO can proceed. This is the case 0da7ca4c4fd9 was written for. > The other callers either cannot run while the host is suspended or > already hold their own PM reference, so they never exercise the > resume path. So then could the RPM resume calls be moved higher up, like at the smp_execute_task_sg() callsite? Would that work? The check which you initially proposed for testing SAS_HA_RESUMING looks racy. > > log as follow: > [root@localhost ~]# smp_discover /dev/bsg/expander-5\:0 >   phy  11:U:attached:[5446a2eb02349000:00  t(SSP)]  12 Gbps >   phy  16:U:attached:[5001882016000001:00  i(SSP+STP+SMP)]  12 Gbps >   phy  17:U:attached:[5001882016000001:01  i(SSP+STP+SMP)]  12 Gbps >   phy  18:U:attached:[5001882016000001:02  i(SSP+STP+SMP)]  12 Gbps >   phy  19:U:attached:[5001882016000001:03  i(SSP+STP+SMP)]  12 Gbps >   phy  24:D:attached:[500e004aaaaaaa1e:24  V i(SSP) t(SSP)]  12 Gbps > > [47910.943602] jamy pm_runtime_resume_and_get(ha->dev) > [47910.969905] hisi_sas_v3_hw 0000:74:04.0: resuming from operating > state [D0] > [47912.205965] hisi_sas_v3_hw 0000:74:04.0: neither _PS0 nor _PR0 is > defined > [47912.213852] hisi_sas_v3_hw 0000:74:04.0: waiting up to 25 seconds for > 4 phys to resume > [47912.268896] hisi_sas_v3_hw 0000:74:04.0: phyup: phy0 link_rate=11 > [47912.275986] hisi_sas_v3_hw 0000:74:04.0: phyup: phy1 link_rate=11 > [47912.276017] hisi_sas_v3_hw 0000:74:04.0: dev[7:2] found > [47912.282976] hisi_sas_v3_hw 0000:74:04.0: phyup: phy2 link_rate=11 > [47912.282980] hisi_sas_v3_hw 0000:74:04.0: phyup: phy3 link_rate=11 > [47912.303834] hisi_sas_v3_hw 0000:74:04.0: dev[8:1] found > [47912.310296] hisi_sas_v3_hw 0000:74:04.0: dev[9:1] found > [47912.316809] hisi_sas_v3_hw 0000:74:04.0: end of resuming controller > [47912.316817] sas: broadcast received: 0 > [47912.324219] sas: REVALIDATING DOMAIN on port 0, pid:282487 > [47912.329870] jamy pm_runtime_put(ha->dev)