From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751185AbaC1GeE (ORCPT ); Fri, 28 Mar 2014 02:34:04 -0400 Received: from am1ehsobe003.messaging.microsoft.com ([213.199.154.206]:34576 "EHLO am1outboundpool.messaging.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751006AbaC1GeC (ORCPT ); Fri, 28 Mar 2014 02:34:02 -0400 X-Forefront-Antispam-Report: CIP:70.37.183.190;KIP:(null);UIP:(null);IPV:NLI;H:mail.freescale.net;RD:none;EFVD:NLI X-SpamScore: -5 X-BigFish: VS-5(zzbb2dI98dI9371I936eI1432Id799hzz1f42h2148h208ch1ee6h1de0h1fdah2073h2146h1202h1e76h2189h1d1ah1d2ah21bch1fc6hzz1de098h8275bh1de097hz2dh2a8h839h93fhd25he5bhf0ah1288h12a5h12a9h12bdh137ah13b6h1441h1504h1537h153bh162dh1631h1758h1765h18e1h190ch1946h19b4h19c3h1ad9h1b0ah1b2fh2222h224fh1fb3h1d0ch1d2eh1d3fh1dfeh1dffh1f5fh1fe8h1ff5h209eh22d0h2336h2438h2461h2487h24d7h2516h2545h255eh25cch25f6h2605h268bh1155h) Message-ID: <533517C1.8080208@freescale.com> Date: Fri, 28 Mar 2014 14:33:37 +0800 From: Hongbo Zhang User-Agent: Mozilla/5.0 (X11; Linux i686; rv:24.0) Gecko/20100101 Thunderbird/24.1.1 MIME-Version: 1.0 To: Vinod Koul CC: , , , , , , Subject: Re: [PATCH 6/7] DMA: Freescale: use spin_lock_bh instead of spin_lock_irqsave References: <1389851246-8564-1-git-send-email-hongbo.zhang@freescale.com> <1389851246-8564-7-git-send-email-hongbo.zhang@freescale.com> <1395817294.6569.2.camel@vkoul-udesk3> In-Reply-To: <1395817294.6569.2.camel@vkoul-udesk3> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-OriginatorOrg: freescale.com X-FOPE-CONNECTOR: Id%0$Dn%*$RO%0$TLS%0$FQDN%$TlsDn% X-FOPE-CONNECTOR: Id%0$Dn%FREESCALE.MAIL.ONMICROSOFT.COM$RO%1$TLS%0$FQDN%$TlsDn% Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/26/2014 03:01 PM, Vinod Koul wrote: > On Thu, 2014-01-16 at 13:47 +0800, hongbo.zhang@freescale.com wrote: >> From: Hongbo Zhang >> >> The usage of spin_lock_irqsave() is a stronger locking mechanism than is >> required throughout the driver. The minimum locking required should be used >> instead. Interrupts will be turned off and context will be saved, it is >> unnecessary to use irqsave. >> >> This patch changes all instances of spin_lock_irqsave() to spin_lock_bh(). All >> manipulation of protected fields is done using tasklet context or weaker, which >> makes spin_lock_bh() the correct choice. >> >> Signed-off-by: Hongbo Zhang >> Signed-off-by: Qiang Liu >> --- >> drivers/dma/fsldma.c | 25 ++++++++++--------------- >> 1 file changed, 10 insertions(+), 15 deletions(-) >> >> diff --git a/drivers/dma/fsldma.c b/drivers/dma/fsldma.c >> index bbace54..437794e 100644 >> --- a/drivers/dma/fsldma.c >> +++ b/drivers/dma/fsldma.c >> @@ -396,10 +396,9 @@ static dma_cookie_t fsl_dma_tx_submit(struct dma_async_tx_descriptor *tx) >> struct fsldma_chan *chan = to_fsl_chan(tx->chan); >> struct fsl_desc_sw *desc = tx_to_fsl_desc(tx); >> struct fsl_desc_sw *child; >> - unsigned long flags; >> dma_cookie_t cookie = -EINVAL; >> >> - spin_lock_irqsave(&chan->desc_lock, flags); >> + spin_lock_bh(&chan->desc_lock); >> >> /* >> * assign cookies to all of the software descriptors >> @@ -412,7 +411,7 @@ static dma_cookie_t fsl_dma_tx_submit(struct dma_async_tx_descriptor *tx) >> /* put this transaction onto the tail of the pending queue */ >> append_ld_queue(chan, desc); >> >> - spin_unlock_irqrestore(&chan->desc_lock, flags); >> + spin_unlock_bh(&chan->desc_lock); >> >> return cookie; >> } >> @@ -731,15 +730,14 @@ static void fsldma_free_desc_list_reverse(struct fsldma_chan *chan, >> static void fsl_dma_free_chan_resources(struct dma_chan *dchan) >> { >> struct fsldma_chan *chan = to_fsl_chan(dchan); >> - unsigned long flags; >> >> chan_dbg(chan, "free all channel resources\n"); >> - spin_lock_irqsave(&chan->desc_lock, flags); >> + spin_lock_bh(&chan->desc_lock); >> fsldma_cleanup_descriptors(chan); >> fsldma_free_desc_list(chan, &chan->ld_pending); >> fsldma_free_desc_list(chan, &chan->ld_running); >> fsldma_free_desc_list(chan, &chan->ld_completed); >> - spin_unlock_irqrestore(&chan->desc_lock, flags); >> + spin_unlock_bh(&chan->desc_lock); >> >> dma_pool_destroy(chan->desc_pool); >> chan->desc_pool = NULL; >> @@ -958,7 +956,6 @@ static int fsl_dma_device_control(struct dma_chan *dchan, >> { >> struct dma_slave_config *config; >> struct fsldma_chan *chan; >> - unsigned long flags; >> int size; >> >> if (!dchan) >> @@ -968,7 +965,7 @@ static int fsl_dma_device_control(struct dma_chan *dchan, >> >> switch (cmd) { >> case DMA_TERMINATE_ALL: >> - spin_lock_irqsave(&chan->desc_lock, flags); >> + spin_lock_bh(&chan->desc_lock); >> >> /* Halt the DMA engine */ >> dma_halt(chan); >> @@ -979,7 +976,7 @@ static int fsl_dma_device_control(struct dma_chan *dchan, >> fsldma_free_desc_list(chan, &chan->ld_completed); >> chan->idle = true; >> >> - spin_unlock_irqrestore(&chan->desc_lock, flags); >> + spin_unlock_bh(&chan->desc_lock); >> return 0; >> >> case DMA_SLAVE_CONFIG: >> @@ -1021,11 +1018,10 @@ static int fsl_dma_device_control(struct dma_chan *dchan, >> static void fsl_dma_memcpy_issue_pending(struct dma_chan *dchan) >> { >> struct fsldma_chan *chan = to_fsl_chan(dchan); >> - unsigned long flags; >> >> - spin_lock_irqsave(&chan->desc_lock, flags); >> + spin_lock_bh(&chan->desc_lock); >> fsl_chan_xfer_ld_queue(chan); >> - spin_unlock_irqrestore(&chan->desc_lock, flags); >> + spin_unlock_bh(&chan->desc_lock); >> } >> >> /** >> @@ -1124,11 +1120,10 @@ static irqreturn_t fsldma_chan_irq(int irq, void *data) >> static void dma_do_tasklet(unsigned long data) >> { >> struct fsldma_chan *chan = (struct fsldma_chan *)data; >> - unsigned long flags; >> >> chan_dbg(chan, "tasklet entry\n"); >> >> - spin_lock_irqsave(&chan->desc_lock, flags); >> + spin_lock_bh(&chan->desc_lock); > okay here is the problem :( > > You moved to _bh variant. So if you grab the lock in rest of the code > and irq gets triggered then here we will be spinning to grab the lock. > So effectively you made right locking solution into deadlock situation! If the rest code grabs lock by spin_lock_bh(), and if irq raised, the tasklet could not be executed because it has been disabled by the _bh variant function. Right? >> >> /* the hardware is now idle and ready for more */ >> chan->idle = true; >> @@ -1136,7 +1131,7 @@ static void dma_do_tasklet(unsigned long data) >> /* Run all cleanup for descriptors which have been completed */ >> fsldma_cleanup_descriptors(chan); >> >> - spin_unlock_irqrestore(&chan->desc_lock, flags); >> + spin_unlock_bh(&chan->desc_lock); >> >> chan_dbg(chan, "tasklet exit\n"); >> } >