From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3st3SL5GkRzDrbq for ; Tue, 11 Oct 2016 02:09:21 +1100 (AEDT) Received: from pps.filterd (m0098421.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.17/8.16.0.17) with SMTP id u9AF4JDZ074505 for ; Mon, 10 Oct 2016 11:09:18 -0400 Received: from e06smtp14.uk.ibm.com (e06smtp14.uk.ibm.com [195.75.94.110]) by mx0a-001b2d01.pphosted.com with ESMTP id 260cc3ayb8-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 10 Oct 2016 11:09:18 -0400 Received: from localhost by e06smtp14.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 10 Oct 2016 16:09:16 +0100 Received: from b06cxnps4074.portsmouth.uk.ibm.com (d06relay11.portsmouth.uk.ibm.com [9.149.109.196]) by d06dlp02.portsmouth.uk.ibm.com (Postfix) with ESMTP id 4B9C1219005F for ; Mon, 10 Oct 2016 16:08:32 +0100 (BST) Received: from d06av08.portsmouth.uk.ibm.com (d06av08.portsmouth.uk.ibm.com [9.149.37.249]) by b06cxnps4074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u9AF9Eov17629418 for ; Mon, 10 Oct 2016 15:09:14 GMT Received: from d06av08.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av08.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u9AF9Daa011215 for ; Mon, 10 Oct 2016 09:09:14 -0600 Subject: Re: [PATCH] cxl: Prevent adapter reset if an active context exists To: Vaibhav Jain , linuxppc-dev@lists.ozlabs.org References: <1476108550-31686-1-git-send-email-vaibhav@linux.vnet.ibm.com> Cc: Ian Munsie , Andrew Donnellan From: Frederic Barrat Date: Mon, 10 Oct 2016 17:09:07 +0200 MIME-Version: 1.0 In-Reply-To: <1476108550-31686-1-git-send-email-vaibhav@linux.vnet.ibm.com> Content-Type: text/plain; charset=windows-1252; format=flowed Message-Id: List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Hi Vaibhav, A few comments below... Le 10/10/2016 à 16:09, Vaibhav Jain a écrit : > This patch prevents resetting the cxl adapter via sysfs in presence of > one or more active cxl_context on it. This protects against an > unrecoverable error caused by PSL owning a dirty cache line even after > reset and host tries to touch the same cache line. In case a force reset > of the card is required irrespective of any active contexts, the int > value -1 can be stored in the 'reset' sysfs attribute of the card. > > The patch introduces a new atomic_t member named contexts_num inside > struct cxl that holds the number of active context attached to the card > , which is checked against '0' before proceeding with the reset. To > prevent against a race condition where a context is activated just after > reset check is performed, the contexts_num is atomically set to '-1' > after reset-check to indicate that no more contexts can be activated on > the card anymore. > > Before activating a context we atomically test if contexts_num is > non-negative and if so, increment its value by one. In case the value of > contexts_num is negative then it indicates that the card is about to be > reset and context activation is error-ed out at that point. > > Signed-off-by: Vaibhav Jain > Reviewed-by: Andrew Donnellan > --- > Documentation/ABI/testing/sysfs-class-cxl | 7 +++++-- > drivers/misc/cxl/api.c | 9 +++++++++ > drivers/misc/cxl/context.c | 3 +++ > drivers/misc/cxl/cxl.h | 21 +++++++++++++++++++++ > drivers/misc/cxl/file.c | 9 +++++++++ > drivers/misc/cxl/main.c | 24 +++++++++++++++++++++++- > drivers/misc/cxl/sysfs.c | 18 ++++++++++++++---- > 7 files changed, 84 insertions(+), 7 deletions(-) > > diff --git a/Documentation/ABI/testing/sysfs-class-cxl b/Documentation/ABI/testing/sysfs-class-cxl > index 4ba0a2a..dae2b38 100644 > --- a/Documentation/ABI/testing/sysfs-class-cxl > +++ b/Documentation/ABI/testing/sysfs-class-cxl > @@ -220,8 +220,11 @@ What: /sys/class/cxl//reset > Date: October 2014 > Contact: linuxppc-dev@lists.ozlabs.org > Description: write only > - Writing 1 will issue a PERST to card which may cause the card > - to reload the FPGA depending on load_image_on_perst. > + Writing 1 will issue a PERST to card provided there are no > + contexts active on any one of the card AFUs. This may cause > + the card to reload the FPGA depending on load_image_on_perst. > + Writing -1 will do a force PERST irrespective of any active > + contexts on the card AFUs. > Users: https://github.com/ibm-capi/libcxl > > What: /sys/class/cxl//perst_reloads_same_image (not in a guest) > diff --git a/drivers/misc/cxl/api.c b/drivers/misc/cxl/api.c > index f3d34b9..85bb2d9 100644 > --- a/drivers/misc/cxl/api.c > +++ b/drivers/misc/cxl/api.c > @@ -236,10 +236,19 @@ int cxl_start_context(struct cxl_context *ctx, u64 wed, > ctx->real_mode = false; > } > > + /* > + * Increment the mapped context count for adapter. This also checks > + * if adapter_context_lock is taken. > + */ > + rc = cxl_adapter_context_get(ctx->afu->adapter); > + if (rc) > + goto out; > + > cxl_ctx_get(); > > if ((rc = cxl_ops->attach_process(ctx, kernel, wed, 0))) { > put_pid(ctx->pid); > + cxl_adapter_context_put(ctx->afu->adapter); > cxl_ctx_put(); > goto out; > } > diff --git a/drivers/misc/cxl/context.c b/drivers/misc/cxl/context.c > index c466ee2..5e506c1 100644 > --- a/drivers/misc/cxl/context.c > +++ b/drivers/misc/cxl/context.c > @@ -238,6 +238,9 @@ int __detach_context(struct cxl_context *ctx) > put_pid(ctx->glpid); > > cxl_ctx_put(); > + > + /* Decrease the attached context count on the adapter */ > + cxl_adapter_context_put(ctx->afu->adapter); > return 0; > } > > diff --git a/drivers/misc/cxl/cxl.h b/drivers/misc/cxl/cxl.h > index 01d372a..ed89c57 100644 > --- a/drivers/misc/cxl/cxl.h > +++ b/drivers/misc/cxl/cxl.h > @@ -618,6 +618,14 @@ struct cxl { > bool perst_select_user; > bool perst_same_image; > bool psl_timebase_synced; > + > + /* > + * number of contexts mapped on to this card. > + * +ve: Number of contexts mapped and new one can be mapped. > + * 0 : No active contexts and new ones can be mapped. > + * -ve: No contexts mapped and new ones cannot be mapped. what does "ve" stand for ? For the last one, shouldn't it be '-1' ? > + */ > + atomic_t contexts_num; > }; > > int cxl_pci_alloc_one_irq(struct cxl *adapter); > @@ -944,4 +952,17 @@ bool cxl_pci_is_vphb_device(struct pci_dev *dev); > > /* decode AFU error bits in the PSL register PSL_SERR_An */ > void cxl_afu_decode_psl_serr(struct cxl_afu *afu, u64 serr); > + > +/* > + * Increments the number of attached contexts on an adapter. > + * Incase an adapter_context_lock is taken the return -EBUSY. typo "In case" > + */ > +int cxl_adapter_context_get(struct cxl *adapter); > + > +/* Decrements the number of attached contexts on an adapter */ > +void cxl_adapter_context_put(struct cxl *adapter); > + > +/* If no active contexts then prevents contexts from being attached */ > +int cxl_adapter_context_lock(struct cxl *adapter); > + > #endif > diff --git a/drivers/misc/cxl/file.c b/drivers/misc/cxl/file.c > index 5fb9894..3b2272a 100644 > --- a/drivers/misc/cxl/file.c > +++ b/drivers/misc/cxl/file.c > @@ -205,11 +205,20 @@ static long afu_ioctl_start_work(struct cxl_context *ctx, > ctx->pid = get_task_pid(current, PIDTYPE_PID); > ctx->glpid = get_task_pid(current->group_leader, PIDTYPE_PID); > > + /* > + * Increment the mapped context count for adapter. This also checks > + * if adapter_context_lock is taken. > + */ > + rc = cxl_adapter_context_get(ctx->afu->adapter); > + if (rc) > + goto out; > + We are missing a call to afu_release_irqs() in case of error here. > trace_cxl_attach(ctx, work.work_element_descriptor, work.num_interrupts, amr); > > if ((rc = cxl_ops->attach_process(ctx, false, work.work_element_descriptor, > amr))) { > afu_release_irqs(ctx, ctx); > + cxl_adapter_context_put(ctx->afu->adapter); > goto out; > } > > diff --git a/drivers/misc/cxl/main.c b/drivers/misc/cxl/main.c > index d9be23b2..5c3c02a 100644 > --- a/drivers/misc/cxl/main.c > +++ b/drivers/misc/cxl/main.c > @@ -243,8 +243,9 @@ struct cxl *cxl_alloc_adapter(void) > if (dev_set_name(&adapter->dev, "card%i", adapter->adapter_num)) > goto err2; > > - return adapter; > + atomic_set(&adapter->contexts_num, 0); I think the initialization of the counter should be done in cxl_configure_adapter() instead of cxl_alloc_adapter(). I would expect most reset scenarios to end up unloading/reloading the driver, but if you look at cxl_pci_error_detected(), it should be possible to tweak some settings to just deconfigure/reconfigure the adapter. So it seems safer to reset the counter to 0 in cxl_configure_adapter(). Also wouldn't it make sense to add a WARN if the counter is not NULL when unconfiguring the adapter? It seems that it would be a bug. > + return adapter; > err2: > cxl_remove_adapter_nr(adapter); > err1: > @@ -286,6 +287,27 @@ int cxl_afu_select_best_mode(struct cxl_afu *afu) > return 0; > } > > +int cxl_adapter_context_get(struct cxl *adapter) > +{ > + int rc; > + > + rc = atomic_inc_unless_negative(&adapter->contexts_num); > + return rc >= 0 ? 0 : -EBUSY; > +} > + > +void cxl_adapter_context_put(struct cxl *adapter) > +{ > + atomic_dec_if_positive(&adapter->contexts_num); > +} > + > +int cxl_adapter_context_lock(struct cxl *adapter) > +{ > + int rc; > + /* no active contexts -> contexts_num == 0 */ > + rc = atomic_cmpxchg(&adapter->contexts_num, 0, -1); > + return rc ? -EBUSY : 0; > +} > + > static int __init init_cxl(void) > { > int rc = 0; > diff --git a/drivers/misc/cxl/sysfs.c b/drivers/misc/cxl/sysfs.c > index b043c20..592dbf2 100644 > --- a/drivers/misc/cxl/sysfs.c > +++ b/drivers/misc/cxl/sysfs.c > @@ -75,12 +75,22 @@ static ssize_t reset_adapter_store(struct device *device, > int val; > > rc = sscanf(buf, "%i", &val); > - if ((rc != 1) || (val != 1)) > + if ((rc != 1) || (val != 1 && val != -1)) > return -EINVAL; > > - if ((rc = cxl_ops->adapter_reset(adapter))) > - return rc; > - return count; > + /* > + * See if we can lock the context mapping that's only allowed > + * when there are no contexts attached to the adapter. Once > + * taken this will also prevent any context being attached. > + */ > + if (val == 1) > + rc = cxl_adapter_context_lock(adapter); > + > + /* Perform a forced adapter reset */ > + if (rc >= 0) > + rc = cxl_ops->adapter_reset(adapter); Readability could be improved, rc meaning seems overloaded. Also, if the adapter_reset callback fails, we need to reset the count. Fred > + > + return rc ? rc : count; > } > > static ssize_t load_image_on_perst_show(struct device *device, >