diff mbox series

[RFC,v2,8/8] dax: Fix incorrect list of dcache aliasing architectures

Message ID 20240130165255.212591-9-mathieu.desnoyers@efficios.com
State New
Headers
Series Introduce dcache_is_aliasing() to fix DAX regression |

Commit Message

Mathieu Desnoyers Jan. 30, 2024, 4:52 p.m. UTC 
  commit d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
prevents DAX from building on architectures with virtually aliased
dcache with:

  depends on !(ARM || MIPS || SPARC)

This check is too broad (e.g. recent ARMv7 don't have virtually aliased
dcaches), and also misses many other architectures with virtually
aliased dcache.

This is a regression introduced in the v5.13 Linux kernel where the
dax mount option is removed for 32-bit ARMv7 boards which have no dcache
aliasing, and therefore should work fine with FS_DAX.

This was turned into the following implementation of dax_is_supported()
by a preparatory change:

        return !IS_ENABLED(CONFIG_ARM) &&
               !IS_ENABLED(CONFIG_MIPS) &&
               !IS_ENABLED(CONFIG_SPARC);

Use dcache_is_aliasing() instead to figure out whether the environment
has aliasing dcaches.

Fixes: d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: linux-arch@vger.kernel.org
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Russell King <linux@armlinux.org.uk>
Cc: nvdimm@lists.linux.dev
Cc: linux-cxl@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
---
 include/linux/dax.h | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

Comments

Dave Chinner Jan. 31, 2024, 2:54 a.m. UTC | #1 
On Tue, Jan 30, 2024 at 11:52:55AM -0500, Mathieu Desnoyers wrote:
> commit d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
> prevents DAX from building on architectures with virtually aliased
> dcache with:
> 
>   depends on !(ARM || MIPS || SPARC)
> 
> This check is too broad (e.g. recent ARMv7 don't have virtually aliased
> dcaches), and also misses many other architectures with virtually
> aliased dcache.
> 
> This is a regression introduced in the v5.13 Linux kernel where the
> dax mount option is removed for 32-bit ARMv7 boards which have no dcache
> aliasing, and therefore should work fine with FS_DAX.
> 
> This was turned into the following implementation of dax_is_supported()
> by a preparatory change:
> 
>         return !IS_ENABLED(CONFIG_ARM) &&
>                !IS_ENABLED(CONFIG_MIPS) &&
>                !IS_ENABLED(CONFIG_SPARC);
> 
> Use dcache_is_aliasing() instead to figure out whether the environment
> has aliasing dcaches.
> 
> Fixes: d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: linux-mm@kvack.org
> Cc: linux-arch@vger.kernel.org
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Vishal Verma <vishal.l.verma@intel.com>
> Cc: Dave Jiang <dave.jiang@intel.com>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Russell King <linux@armlinux.org.uk>
> Cc: nvdimm@lists.linux.dev
> Cc: linux-cxl@vger.kernel.org
> Cc: linux-fsdevel@vger.kernel.org
> ---
>  include/linux/dax.h | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index cfc8cd4a3eae..f59e604662e4 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -5,6 +5,7 @@
>  #include <linux/fs.h>
>  #include <linux/mm.h>
>  #include <linux/radix-tree.h>
> +#include <linux/cacheinfo.h>
>  
>  typedef unsigned long dax_entry_t;
>  
> @@ -80,9 +81,7 @@ static inline bool daxdev_mapping_supported(struct vm_area_struct *vma,
>  }
>  static inline bool dax_is_supported(void)
>  {
> -	return !IS_ENABLED(CONFIG_ARM) &&
> -	       !IS_ENABLED(CONFIG_MIPS) &&
> -	       !IS_ENABLED(CONFIG_SPARC);
> +	return !dcache_is_aliasing();

Yeah, if this is just a one liner should go into
fs_dax_get_by_bdev(), similar to the blk_queue_dax() check at the
start of the function.

I also noticed that device mapper uses fs_dax_get_by_bdev() to
determine if it can support DAX, but this patch set does not address
that case. Hence it really seems to me like fs_dax_get_by_bdev() is
the right place to put this check.

-Dave.
Dan Williams Jan. 31, 2024, 3:13 a.m. UTC | #2 
Dave Chinner wrote:
> On Tue, Jan 30, 2024 at 11:52:55AM -0500, Mathieu Desnoyers wrote:
> > commit d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
> > prevents DAX from building on architectures with virtually aliased
> > dcache with:
> > 
> >   depends on !(ARM || MIPS || SPARC)
> > 
> > This check is too broad (e.g. recent ARMv7 don't have virtually aliased
> > dcaches), and also misses many other architectures with virtually
> > aliased dcache.
> > 
> > This is a regression introduced in the v5.13 Linux kernel where the
> > dax mount option is removed for 32-bit ARMv7 boards which have no dcache
> > aliasing, and therefore should work fine with FS_DAX.
> > 
> > This was turned into the following implementation of dax_is_supported()
> > by a preparatory change:
> > 
> >         return !IS_ENABLED(CONFIG_ARM) &&
> >                !IS_ENABLED(CONFIG_MIPS) &&
> >                !IS_ENABLED(CONFIG_SPARC);
> > 
> > Use dcache_is_aliasing() instead to figure out whether the environment
> > has aliasing dcaches.
> > 
> > Fixes: d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
> > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Linus Torvalds <torvalds@linux-foundation.org>
> > Cc: linux-mm@kvack.org
> > Cc: linux-arch@vger.kernel.org
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Cc: Vishal Verma <vishal.l.verma@intel.com>
> > Cc: Dave Jiang <dave.jiang@intel.com>
> > Cc: Matthew Wilcox <willy@infradead.org>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Russell King <linux@armlinux.org.uk>
> > Cc: nvdimm@lists.linux.dev
> > Cc: linux-cxl@vger.kernel.org
> > Cc: linux-fsdevel@vger.kernel.org
> > ---
> >  include/linux/dax.h | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> > 
> > diff --git a/include/linux/dax.h b/include/linux/dax.h
> > index cfc8cd4a3eae..f59e604662e4 100644
> > --- a/include/linux/dax.h
> > +++ b/include/linux/dax.h
> > @@ -5,6 +5,7 @@
> >  #include <linux/fs.h>
> >  #include <linux/mm.h>
> >  #include <linux/radix-tree.h>
> > +#include <linux/cacheinfo.h>
> >  
> >  typedef unsigned long dax_entry_t;
> >  
> > @@ -80,9 +81,7 @@ static inline bool daxdev_mapping_supported(struct vm_area_struct *vma,
> >  }
> >  static inline bool dax_is_supported(void)
> >  {
> > -	return !IS_ENABLED(CONFIG_ARM) &&
> > -	       !IS_ENABLED(CONFIG_MIPS) &&
> > -	       !IS_ENABLED(CONFIG_SPARC);
> > +	return !dcache_is_aliasing();
> 
> Yeah, if this is just a one liner should go into
> fs_dax_get_by_bdev(), similar to the blk_queue_dax() check at the
> start of the function.
> 
> I also noticed that device mapper uses fs_dax_get_by_bdev() to
> determine if it can support DAX, but this patch set does not address
> that case. Hence it really seems to me like fs_dax_get_by_bdev() is
> the right place to put this check.

Oh, good catch. Yes, I agree this can definitely be pushed down, but
then I think it should be pushed down all the way to make alloc_dax()
fail. That will need some additional fixups like:

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 8dcabf84d866..a35e60e62440 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2126,12 +2126,12 @@ static struct mapped_device *alloc_dev(int minor)
                md->dax_dev = alloc_dax(md, &dm_dax_ops);
                if (IS_ERR(md->dax_dev)) {
                        md->dax_dev = NULL;
-                       goto bad;
+               } else {
+                       set_dax_nocache(md->dax_dev);
+                       set_dax_nomc(md->dax_dev);
+                       if (dax_add_host(md->dax_dev, md->disk))
+                               goto bad;
                }
-               set_dax_nocache(md->dax_dev);
-               set_dax_nomc(md->dax_dev);
-               if (dax_add_host(md->dax_dev, md->disk))
-                       goto bad;
        }
 
        format_dev_t(md->name, MKDEV(_major, minor));

..to make it not fatal to fail to register the dax_dev.
Mathieu Desnoyers Jan. 31, 2024, 3:14 p.m. UTC | #3 
On 2024-01-30 22:13, Dan Williams wrote:
> Dave Chinner wrote:
>> On Tue, Jan 30, 2024 at 11:52:55AM -0500, Mathieu Desnoyers wrote:
>>> commit d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
>>> prevents DAX from building on architectures with virtually aliased
>>> dcache with:
>>>
>>>    depends on !(ARM || MIPS || SPARC)
>>>
>>> This check is too broad (e.g. recent ARMv7 don't have virtually aliased
>>> dcaches), and also misses many other architectures with virtually
>>> aliased dcache.
>>>
>>> This is a regression introduced in the v5.13 Linux kernel where the
>>> dax mount option is removed for 32-bit ARMv7 boards which have no dcache
>>> aliasing, and therefore should work fine with FS_DAX.
>>>
>>> This was turned into the following implementation of dax_is_supported()
>>> by a preparatory change:
>>>
>>>          return !IS_ENABLED(CONFIG_ARM) &&
>>>                 !IS_ENABLED(CONFIG_MIPS) &&
>>>                 !IS_ENABLED(CONFIG_SPARC);
>>>
>>> Use dcache_is_aliasing() instead to figure out whether the environment
>>> has aliasing dcaches.
>>>
>>> Fixes: d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
>>> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>> Cc: Linus Torvalds <torvalds@linux-foundation.org>
>>> Cc: linux-mm@kvack.org
>>> Cc: linux-arch@vger.kernel.org
>>> Cc: Dan Williams <dan.j.williams@intel.com>
>>> Cc: Vishal Verma <vishal.l.verma@intel.com>
>>> Cc: Dave Jiang <dave.jiang@intel.com>
>>> Cc: Matthew Wilcox <willy@infradead.org>
>>> Cc: Arnd Bergmann <arnd@arndb.de>
>>> Cc: Russell King <linux@armlinux.org.uk>
>>> Cc: nvdimm@lists.linux.dev
>>> Cc: linux-cxl@vger.kernel.org
>>> Cc: linux-fsdevel@vger.kernel.org
>>> ---
>>>   include/linux/dax.h | 5 ++---
>>>   1 file changed, 2 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/include/linux/dax.h b/include/linux/dax.h
>>> index cfc8cd4a3eae..f59e604662e4 100644
>>> --- a/include/linux/dax.h
>>> +++ b/include/linux/dax.h
>>> @@ -5,6 +5,7 @@
>>>   #include <linux/fs.h>
>>>   #include <linux/mm.h>
>>>   #include <linux/radix-tree.h>
>>> +#include <linux/cacheinfo.h>
>>>   
>>>   typedef unsigned long dax_entry_t;
>>>   
>>> @@ -80,9 +81,7 @@ static inline bool daxdev_mapping_supported(struct vm_area_struct *vma,
>>>   }
>>>   static inline bool dax_is_supported(void)
>>>   {
>>> -	return !IS_ENABLED(CONFIG_ARM) &&
>>> -	       !IS_ENABLED(CONFIG_MIPS) &&
>>> -	       !IS_ENABLED(CONFIG_SPARC);
>>> +	return !dcache_is_aliasing();
>>
>> Yeah, if this is just a one liner should go into
>> fs_dax_get_by_bdev(), similar to the blk_queue_dax() check at the
>> start of the function.
>>
>> I also noticed that device mapper uses fs_dax_get_by_bdev() to
>> determine if it can support DAX, but this patch set does not address
>> that case. Hence it really seems to me like fs_dax_get_by_bdev() is
>> the right place to put this check.
> 
> Oh, good catch. Yes, I agree this can definitely be pushed down, but
> then I think it should be pushed down all the way to make alloc_dax()
> fail. That will need some additional fixups like:
> 
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 8dcabf84d866..a35e60e62440 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -2126,12 +2126,12 @@ static struct mapped_device *alloc_dev(int minor)
>                  md->dax_dev = alloc_dax(md, &dm_dax_ops);
>                  if (IS_ERR(md->dax_dev)) {
>                          md->dax_dev = NULL;
> -                       goto bad;
> +               } else {
> +                       set_dax_nocache(md->dax_dev);
> +                       set_dax_nomc(md->dax_dev);
> +                       if (dax_add_host(md->dax_dev, md->disk))
> +                               goto bad;
>                  }
> -               set_dax_nocache(md->dax_dev);
> -               set_dax_nomc(md->dax_dev);
> -               if (dax_add_host(md->dax_dev, md->disk))
> -                       goto bad;
>          }
>   
>          format_dev_t(md->name, MKDEV(_major, minor));
> 
> ...to make it not fatal to fail to register the dax_dev.

I've had a quick look at other users of alloc_dax() and
alloc_dax_region(), and so far I figure that all of those
really want to bail out on alloc_dax failure. Is dm.c the
only special-case we need to fix to make it non-fatal ?

Thanks,

Mathieu
diff mbox series

Patch

diff --git a/include/linux/dax.h b/include/linux/dax.h
index cfc8cd4a3eae..f59e604662e4 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -5,6 +5,7 @@ 
 #include <linux/fs.h>
 #include <linux/mm.h>
 #include <linux/radix-tree.h>
+#include <linux/cacheinfo.h>
 
 typedef unsigned long dax_entry_t;
 
@@ -80,9 +81,7 @@  static inline bool daxdev_mapping_supported(struct vm_area_struct *vma,
 }
 static inline bool dax_is_supported(void)
 {
-	return !IS_ENABLED(CONFIG_ARM) &&
-	       !IS_ENABLED(CONFIG_MIPS) &&
-	       !IS_ENABLED(CONFIG_SPARC);
+	return !dcache_is_aliasing();
 }
 #else
 static inline void *dax_holder(struct dax_device *dax_dev)