Re: [Xen-devel] [PATCH] xen-blkback: allow module to be cleanly unloaded

2019-11-29 Thread Durrant, Paul 
> -Original Message-
> From: Jan Beulich 
> Sent: 29 November 2019 11:56
> To: Durrant, Paul 
> Cc: xen-devel@lists.xenproject.org; linux-bl...@vger.kernel.org; linux-
> ker...@vger.kernel.org; Roger Pau Monné ; Jens Axboe
> ; Konrad Rzeszutek Wilk 
> Subject: Re: [PATCH] xen-blkback: allow module to be cleanly unloaded
> 
> On 29.11.2019 12:31, Paul Durrant wrote:
> > --- a/drivers/block/xen-blkback/xenbus.c
> > +++ b/drivers/block/xen-blkback/xenbus.c
> > @@ -173,6 +173,8 @@ static struct xen_blkif *xen_blkif_alloc(domid_t
> domid)
> > init_completion(>drain_complete);
> > INIT_WORK(>free_work, xen_blkif_deferred_free);
> >
> > +   __module_get(THIS_MODULE);
> > +
> > return blkif;
> >  }
> >
> > @@ -320,6 +322,8 @@ static void xen_blkif_free(struct xen_blkif *blkif)
> >
> > /* Make sure everything is drained before shutting down */
> > kmem_cache_free(xen_blkif_cachep, blkif);
> > +
> > +   module_put(THIS_MODULE);
> >  }
> 
> I realize there are various example of this in the tree, but
> isn't this a flawed approach? __module_get() (nor even
> try_module_get()) will prevent an unload attempt ahead of it
> getting invoked, while execution is already in this module's
> .text section.

Good point. That does appear to be a race.

> I think the xenbus driver should do this
> before calling ->probe(), in case of its failure, and after
> a successful call to ->remove().
> 

That does sound better. I'll see if I can pick up other occurrences (certainly 
netback) and fix.

  Paul
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Re: [Xen-devel] [PATCH] xen-blkback: allow module to be cleanly unloaded

2019-11-29 Thread Jan Beulich 
On 29.11.2019 12:31, Paul Durrant wrote:
> --- a/drivers/block/xen-blkback/xenbus.c
> +++ b/drivers/block/xen-blkback/xenbus.c
> @@ -173,6 +173,8 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid)
>   init_completion(>drain_complete);
>   INIT_WORK(>free_work, xen_blkif_deferred_free);
>  
> + __module_get(THIS_MODULE);
> +
>   return blkif;
>  }
>  
> @@ -320,6 +322,8 @@ static void xen_blkif_free(struct xen_blkif *blkif)
>  
>   /* Make sure everything is drained before shutting down */
>   kmem_cache_free(xen_blkif_cachep, blkif);
> +
> + module_put(THIS_MODULE);
>  }

I realize there are various example of this in the tree, but
isn't this a flawed approach? __module_get() (nor even
try_module_get()) will prevent an unload attempt ahead of it
getting invoked, while execution is already in this module's
.text section. I think the xenbus driver should do this
before calling ->probe(), in case of its failure, and after
a successful call to ->remove().

Jan

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[Xen-devel] [PATCH] xen-blkback: allow module to be cleanly unloaded

2019-11-29 Thread Paul Durrant 
Add a module_exit() to perform the necessary clean-up. Also add
__module_get() and module_put() calls into xen_blkif_alloc() and
xen_blkif_free() respectively to make sure an in-use module cannot be
unloaded.

Signed-off-by: Paul Durrant 
---
Cc: Konrad Rzeszutek Wilk 
Cc: "Roger Pau Monné" 
Cc: Jens Axboe 
---
 drivers/block/xen-blkback/blkback.c |  8 
 drivers/block/xen-blkback/common.h  |  3 +++
 drivers/block/xen-blkback/xenbus.c  | 15 +++
 3 files changed, 26 insertions(+)

diff --git a/drivers/block/xen-blkback/blkback.c 
b/drivers/block/xen-blkback/blkback.c
index fd1e19f1a49f..e562a7e20c3c 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -1504,5 +1504,13 @@ static int __init xen_blkif_init(void)
 
 module_init(xen_blkif_init);
 
+static void __exit xen_blkif_fini(void)
+{
+   xen_blkif_xenbus_fini();
+   xen_blkif_interface_fini();
+}
+
+module_exit(xen_blkif_fini);
+
 MODULE_LICENSE("Dual BSD/GPL");
 MODULE_ALIAS("xen-backend:vbd");
diff --git a/drivers/block/xen-blkback/common.h 
b/drivers/block/xen-blkback/common.h
index 1d3002d773f7..49132b0adbbe 100644
--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -375,9 +375,12 @@ struct phys_req {
struct block_device *bdev;
blkif_sector_t  sector_number;
 };
+
 int xen_blkif_interface_init(void);
+void xen_blkif_interface_fini(void);
 
 int xen_blkif_xenbus_init(void);
+void xen_blkif_xenbus_fini(void);
 
 irqreturn_t xen_blkif_be_int(int irq, void *dev_id);
 int xen_blkif_schedule(void *arg);
diff --git a/drivers/block/xen-blkback/xenbus.c 
b/drivers/block/xen-blkback/xenbus.c
index b90dbcd99c03..f948584fcf66 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -173,6 +173,8 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid)
init_completion(>drain_complete);
INIT_WORK(>free_work, xen_blkif_deferred_free);
 
+   __module_get(THIS_MODULE);
+
return blkif;
 }
 
@@ -320,6 +322,8 @@ static void xen_blkif_free(struct xen_blkif *blkif)
 
/* Make sure everything is drained before shutting down */
kmem_cache_free(xen_blkif_cachep, blkif);
+
+   module_put(THIS_MODULE);
 }
 
 int __init xen_blkif_interface_init(void)
@@ -333,6 +337,12 @@ int __init xen_blkif_interface_init(void)
return 0;
 }
 
+void xen_blkif_interface_fini(void)
+{
+   kmem_cache_destroy(xen_blkif_cachep);
+   xen_blkif_cachep = NULL;
+}
+
 /*
  *  sysfs interface for VBD I/O requests
  */
@@ -1122,3 +1132,8 @@ int xen_blkif_xenbus_init(void)
 {
return xenbus_register_backend(_blkbk_driver);
 }
+
+void xen_blkif_xenbus_fini(void)
+{
+   xenbus_unregister_driver(_blkbk_driver);
+}
-- 
2.20.1


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