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Message-ID: <20181205013444.GX10377@bombadil.infradead.org>
Date: Tue, 4 Dec 2018 17:34:44 -0800
From: Matthew Wilcox <willy@...radead.org>
To: Dan Williams <dan.j.williams@...el.com>
Cc: linux-nvdimm <linux-nvdimm@...ts.01.org>, Jan Kara <jack@...e.cz>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dax: Fix Xarray conversion of dax_unlock_mapping_entry()
On Mon, Dec 03, 2018 at 07:33:43PM -0800, Dan Williams wrote:
> On Fri, Nov 30, 2018 at 12:05 PM Dan Williams <dan.j.williams@...el.com> wrote:
> > > -void dax_unlock_mapping_entry(struct page *page)
> > > +void dax_unlock_mapping_entry(struct page *page, dax_entry_t entry)
> >
> > Let's not require the page to be passed back, it can be derived:
> >
> > page = pfn_to_page(dax_to_pfn((void*) entry));
> >
> > A bit more symmetric that way and canonical with other locking schemes
> > that return a cookie.
>
> The patch does not apply on top of the pending fixes. could resend on
> top of the current libnvdimm-fixes branch [1]?
>
> I think because we are changing the calling convention to take return
> a locked dax_entry_t type, I feel like we should go back to the
> originally proposed names of these interfaces. I.e.
>
> dax_entry_t dax_lock_page(struct page *page)
>
> void dax_unlock_page(dax_entry_t entry)
>
> Yes, it introduces an entry-to-pfn and pfn-to-page conversion.
> However, If I can't convince you to drop the page argument, lets at
> least do the name change. I.e. offload the responsibility of conveying
> that this is not the traditional page lock to the fact that a
> dax_entry is returned and passed back to the unlock routine.
From: Matthew Wilcox <willy@...radead.org>
Date: Fri, 30 Nov 2018 11:05:06 -0500
Subject: [PATCH] dax: Change lock/unlock API
Return the unlock cookie from dax_lock_page() and pass it to
dax_unlock_page(). This fixes a bug where dax_unlock_page() was
assuming that the page was PMD-aligned if the entry was a PMD entry.
Debugged-by: Dan Williams <dan.j.williams@...el.com>
Fixes: 9f32d221301c ("dax: Convert dax_lock_mapping_entry to XArray")
Signed-off-by: Matthew Wilcox <willy@...radead.org>
---
diff --git a/fs/dax.c b/fs/dax.c
index 3f592dc18d67..48132eca3761 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -379,20 +379,20 @@ static struct page *dax_busy_page(void *entry)
* @page: The page whose entry we want to lock
*
* Context: Process context.
- * Return: %true if the entry was locked or does not need to be locked.
+ * Return: A cookie to pass to dax_unlock_page() or 0 if the entry could
+ * not be locked.
*/
-bool dax_lock_mapping_entry(struct page *page)
+dax_entry_t dax_lock_page(struct page *page)
{
XA_STATE(xas, NULL, 0);
void *entry;
- bool locked;
/* Ensure page->mapping isn't freed while we look at it */
rcu_read_lock();
for (;;) {
struct address_space *mapping = READ_ONCE(page->mapping);
- locked = false;
+ entry = NULL;
if (!mapping || !dax_mapping(mapping))
break;
@@ -403,7 +403,7 @@ bool dax_lock_mapping_entry(struct page *page)
* otherwise we would not have a valid pfn_to_page()
* translation.
*/
- locked = true;
+ entry = (void *)~0UL;
if (S_ISCHR(mapping->host->i_mode))
break;
@@ -426,23 +426,18 @@ bool dax_lock_mapping_entry(struct page *page)
break;
}
rcu_read_unlock();
- return locked;
+ return (dax_entry_t)entry;
}
-void dax_unlock_mapping_entry(struct page *page)
+void dax_unlock_page(struct page *page, dax_entry_t cookie)
{
struct address_space *mapping = page->mapping;
XA_STATE(xas, &mapping->i_pages, page->index);
- void *entry;
if (S_ISCHR(mapping->host->i_mode))
return;
- rcu_read_lock();
- entry = xas_load(&xas);
- rcu_read_unlock();
- entry = dax_make_entry(page_to_pfn_t(page), dax_is_pmd_entry(entry));
- dax_unlock_entry(&xas, entry);
+ dax_unlock_entry(&xas, (void *)cookie);
}
/*
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 450b28db9533..0dd316a74a29 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -7,6 +7,8 @@
#include <linux/radix-tree.h>
#include <asm/pgtable.h>
+typedef unsigned long dax_entry_t;
+
struct iomap_ops;
struct dax_device;
struct dax_operations {
@@ -88,8 +90,8 @@ int dax_writeback_mapping_range(struct address_space *mapping,
struct block_device *bdev, struct writeback_control *wbc);
struct page *dax_layout_busy_page(struct address_space *mapping);
-bool dax_lock_mapping_entry(struct page *page);
-void dax_unlock_mapping_entry(struct page *page);
+dax_entry_t dax_lock_page(struct page *page);
+void dax_unlock_page(struct page *page, dax_entry_t cookie);
#else
static inline bool bdev_dax_supported(struct block_device *bdev,
int blocksize)
@@ -122,14 +124,14 @@ static inline int dax_writeback_mapping_range(struct address_space *mapping,
return -EOPNOTSUPP;
}
-static inline bool dax_lock_mapping_entry(struct page *page)
+static inline dax_entry_t dax_lock_page(struct page *page)
{
if (IS_DAX(page->mapping->host))
- return true;
- return false;
+ return ~0UL;
+ return 0;
}
-static inline void dax_unlock_mapping_entry(struct page *page)
+static inline void dax_unlock_page(struct page *page, dax_entry_t cookie)
{
}
#endif
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 0cd3de3550f0..7c72f2a95785 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1161,6 +1161,7 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
LIST_HEAD(tokill);
int rc = -EBUSY;
loff_t start;
+ dax_entry_t cookie;
/*
* Prevent the inode from being freed while we are interrogating
@@ -1169,7 +1170,8 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
* also prevents changes to the mapping of this pfn until
* poison signaling is complete.
*/
- if (!dax_lock_mapping_entry(page))
+ cookie = dax_lock_page(page);
+ if (!cookie)
goto out;
if (hwpoison_filter(page)) {
@@ -1220,7 +1222,7 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
kill_procs(&tokill, flags & MF_MUST_KILL, !unmap_success, pfn, flags);
rc = 0;
unlock:
- dax_unlock_mapping_entry(page);
+ dax_unlock_page(page, cookie);
out:
/* drop pgmap ref acquired in caller */
put_dev_pagemap(pgmap);
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