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Wed, 29 Jul 2020 08:43:29 GMT Received: by smtp.codeaurora.org (Postfix, from userid 1001) id CCED6C433CB; Wed, 29 Jul 2020 08:43:28 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: cang) by smtp.codeaurora.org (Postfix) with ESMTPSA id 988A4C433CA; Wed, 29 Jul 2020 08:43:27 +0000 (UTC) MIME-Version: 1.0 Date: Wed, 29 Jul 2020 16:43:27 +0800 From: Can Guo To: Stanley Chu Subject: Re: [PATCH v2] scsi: ufs: Fix possible infinite loop in ufshcd_hold In-Reply-To: <20200729024037.23105-1-stanley.chu@mediatek.com> References: <20200729024037.23105-1-stanley.chu@mediatek.com> Message-ID: X-Sender: cang@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200729_044342_056142_70761DCA X-CRM114-Status: GOOD ( 20.86 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-scsi@vger.kernel.org, martin.petersen@oracle.com, andy.teng@mediatek.com, jejb@linux.ibm.com, chun-hung.wu@mediatek.com, kuohong.wang@mediatek.com, linux-kernel@vger.kernel.org, asutoshd@codeaurora.org, avri.altman@wdc.com, linux-mediatek@lists.infradead.org, peter.wang@mediatek.com, alim.akhtar@samsung.com, matthias.bgg@gmail.com, beanhuo@micron.com, chaotian.jing@mediatek.com, cc.chou@mediatek.com, linux-arm-kernel@lists.infradead.org, bvanassche@acm.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Stanley, On 2020-07-29 10:40, Stanley Chu wrote: > In ufshcd_suspend(), after clk-gating is suspended and link is set > as Hibern8 state, ufshcd_hold() is still possibly invoked before > ufshcd_suspend() returns. For example, MediaTek's suspend vops may > issue UIC commands which would call ufshcd_hold() during the command > issuing flow. > > Now if UFSHCD_CAP_HIBERN8_WITH_CLK_GATING capability is enabled, > then ufshcd_hold() may enter infinite loops because there is no > clk-ungating work scheduled or pending. In this case, ufshcd_hold() > shall just bypass, and keep the link as Hibern8 state. > The infinite loop is expected as ufshcd_hold is called again after link is put to hibern8 state, so in QCOM's code, we never do this. The cap UFSHCD_CAP_HIBERN8_WITH_CLK_GATING means UIC link state must not be HIBERN8 after ufshcd_hold(async=false) returns. Instead of bailing out from that loop, which makes the logic of ufshcd_hold and clk gating even more complex, how about removing ufshcd_hold/release from ufshcd_send_uic_cmd()? I think they are redundant and we should never send DME cmds if clocks/powers are not ready. I mean callers should make sure they are ready to send DME cmds (and only callers know when), but not leave that job to ufshcd_send_uic_cmd(). It is convenient to remove ufshcd_hold/ release from ufshcd_send_uic_cmd() as there are not many places sending DME cmds without holding the clocks, ufs_bsg.c is one. And I have tested my idea on my setup, it worked well for me. Another benefit is that it also allows us to use DME cmds in clk gating/ungating contexts if we need to in the future. Please let me know your idea, thanks. Can Guo. > Signed-off-by: Stanley Chu > Signed-off-by: Andy Teng > > --- > > Changes since v1: > - Fix return value: Use unique bool variable to get the result of > flush_work(). Thcan prevent incorrect returned value, i.e., rc, if > flush_work() returns true > - Fix commit message > > --- > drivers/scsi/ufs/ufshcd.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c > index 577cc0d7487f..acba2271c5d3 100644 > --- a/drivers/scsi/ufs/ufshcd.c > +++ b/drivers/scsi/ufs/ufshcd.c > @@ -1561,6 +1561,7 @@ static void ufshcd_ungate_work(struct work_struct > *work) > int ufshcd_hold(struct ufs_hba *hba, bool async) > { > int rc = 0; > + bool flush_result; > unsigned long flags; > > if (!ufshcd_is_clkgating_allowed(hba)) > @@ -1592,7 +1593,9 @@ int ufshcd_hold(struct ufs_hba *hba, bool async) > break; > } > spin_unlock_irqrestore(hba->host->host_lock, flags); > - flush_work(&hba->clk_gating.ungate_work); > + flush_result = flush_work(&hba->clk_gating.ungate_work); > + if (hba->clk_gating.is_suspended && !flush_result) > + goto out; > spin_lock_irqsave(hba->host->host_lock, flags); > goto start; > } _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel