Xin Zhong
2010-Dec-07 07:59 UTC
[PATCH] Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
This problem is found in meego testing:
http://bugs.meego.com/show_bug.cgi?id=6672
A file in btrfs is mmaped and the mmaped buffer is passed to pwrite to write to
the same page
of the same file. In btrfs_file_aio_write(), the pages is locked by
prepare_pages(). So when
btrfs_copy_from_user() is called, page fault happens and the same page needs to
be locked again
in filemap_fault(). The fix is to move iov_iter_fault_in_readable() before
prepage_pages() to make page
fault happen before pages are locked. And also disable page fault in critical
region in
btrfs_copy_from_user().
Signed-off-by: Xin Zhong <xin.zhong@intel.com>
---
fs/btrfs/file.c | 23 +++++------------------
1 files changed, 5 insertions(+), 18 deletions(-)
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index dfe15dc..c1faded 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -57,15 +57,11 @@ static noinline int btrfs_copy_from_user(loff_t pos, int
num_pages,
PAGE_CACHE_SIZE - offset, write_bytes);
struct page *page = prepared_pages[pg];
again:
- /*
- * Copy data from userspace to the current page
- *
- * Disable pagefault to avoid recursive lock since the pages
- * are already locked
- */
- pagefault_disable();
- copied = iov_iter_copy_from_user_atomic(page, i, offset, count);
- pagefault_enable();
+ if (unlikely(iov_iter_fault_in_readable(i, count)))
+ return -EFAULT;
+
+ /* Copy data from userspace to the current page */
+ copied = iov_iter_copy_from_user(page, i, offset, count);
/* Flush processor''s dcache for this page */
flush_dcache_page(page);
@@ -978,15 +974,6 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
if (ret)
goto out;
- /*
- * fault pages before locking them in prepare_pages
- * to avoid recursive lock
- */
- if (unlikely(iov_iter_fault_in_readable(&i, write_bytes))) {
- ret = -EFAULT;
- goto out;
- }
-
ret = prepare_pages(root, file, pages, num_pages,
pos, first_index, last_index,
write_bytes);
--
1.6.2.2
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Zhong, Xin
2010-Dec-07 08:46 UTC
RE: [PATCH] Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
The other filesystems such as ext3 do not have this problem since they are using
generic_file_buffered_write(). And this problem is fixed back in 2007 for
generic_file_buffered_write():
http://lkml.org/lkml/2007/2/4/26
I am very new to btrfs. I am wondering why btrfs has it''s own write
routine?
Thanks!
-----Original Message-----
From: Zhong, Xin
Sent: Tuesday, December 07, 2010 4:00 PM
To: linux-btrfs@vger.kernel.org
Cc: Zhong, Xin
Subject: [PATCH] Btrfs: pwrite blocked when writing from the mmaped buffer of
the same page
This problem is found in meego testing:
http://bugs.meego.com/show_bug.cgi?id=6672
A file in btrfs is mmaped and the mmaped buffer is passed to pwrite to write to
the same page
of the same file. In btrfs_file_aio_write(), the pages is locked by
prepare_pages(). So when
btrfs_copy_from_user() is called, page fault happens and the same page needs to
be locked again
in filemap_fault(). The fix is to move iov_iter_fault_in_readable() before
prepage_pages() to make page
fault happen before pages are locked. And also disable page fault in critical
region in
btrfs_copy_from_user().
Signed-off-by: Xin Zhong <xin.zhong@intel.com>
---
fs/btrfs/file.c | 23 +++++------------------
1 files changed, 5 insertions(+), 18 deletions(-)
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index dfe15dc..c1faded 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -57,15 +57,11 @@ static noinline int btrfs_copy_from_user(loff_t pos, int
num_pages,
PAGE_CACHE_SIZE - offset, write_bytes);
struct page *page = prepared_pages[pg];
again:
- /*
- * Copy data from userspace to the current page
- *
- * Disable pagefault to avoid recursive lock since the pages
- * are already locked
- */
- pagefault_disable();
- copied = iov_iter_copy_from_user_atomic(page, i, offset, count);
- pagefault_enable();
+ if (unlikely(iov_iter_fault_in_readable(i, count)))
+ return -EFAULT;
+
+ /* Copy data from userspace to the current page */
+ copied = iov_iter_copy_from_user(page, i, offset, count);
/* Flush processor''s dcache for this page */
flush_dcache_page(page);
@@ -978,15 +974,6 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
if (ret)
goto out;
- /*
- * fault pages before locking them in prepare_pages
- * to avoid recursive lock
- */
- if (unlikely(iov_iter_fault_in_readable(&i, write_bytes))) {
- ret = -EFAULT;
- goto out;
- }
-
ret = prepare_pages(root, file, pages, num_pages,
pos, first_index, last_index,
write_bytes);
--
1.6.2.2
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Zhong, Xin
2010-Dec-07 09:23 UTC
RE: [PATCH] Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
Sorry, the format of the patch is not correct. I will submit again.
-----Original Message-----
From: linux-btrfs-owner@vger.kernel.org
[mailto:linux-btrfs-owner@vger.kernel.org] On Behalf Of Zhong, Xin
Sent: Tuesday, December 07, 2010 4:46 PM
To: linux-btrfs@vger.kernel.org
Subject: RE: [PATCH] Btrfs: pwrite blocked when writing from the mmaped buffer
of the same page
The other filesystems such as ext3 do not have this problem since they are using
generic_file_buffered_write(). And this problem is fixed back in 2007 for
generic_file_buffered_write():
http://lkml.org/lkml/2007/2/4/26
I am very new to btrfs. I am wondering why btrfs has it''s own write
routine?
Thanks!
-----Original Message-----
From: Zhong, Xin
Sent: Tuesday, December 07, 2010 4:00 PM
To: linux-btrfs@vger.kernel.org
Cc: Zhong, Xin
Subject: [PATCH] Btrfs: pwrite blocked when writing from the mmaped buffer of
the same page
This problem is found in meego testing:
http://bugs.meego.com/show_bug.cgi?id=6672
A file in btrfs is mmaped and the mmaped buffer is passed to pwrite to write to
the same page
of the same file. In btrfs_file_aio_write(), the pages is locked by
prepare_pages(). So when
btrfs_copy_from_user() is called, page fault happens and the same page needs to
be locked again
in filemap_fault(). The fix is to move iov_iter_fault_in_readable() before
prepage_pages() to make page
fault happen before pages are locked. And also disable page fault in critical
region in
btrfs_copy_from_user().
Signed-off-by: Xin Zhong <xin.zhong@intel.com>
---
fs/btrfs/file.c | 23 +++++------------------
1 files changed, 5 insertions(+), 18 deletions(-)
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index dfe15dc..c1faded 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -57,15 +57,11 @@ static noinline int btrfs_copy_from_user(loff_t pos, int
num_pages,
PAGE_CACHE_SIZE - offset, write_bytes);
struct page *page = prepared_pages[pg];
again:
- /*
- * Copy data from userspace to the current page
- *
- * Disable pagefault to avoid recursive lock since the pages
- * are already locked
- */
- pagefault_disable();
- copied = iov_iter_copy_from_user_atomic(page, i, offset, count);
- pagefault_enable();
+ if (unlikely(iov_iter_fault_in_readable(i, count)))
+ return -EFAULT;
+
+ /* Copy data from userspace to the current page */
+ copied = iov_iter_copy_from_user(page, i, offset, count);
/* Flush processor''s dcache for this page */
flush_dcache_page(page);
@@ -978,15 +974,6 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
if (ret)
goto out;
- /*
- * fault pages before locking them in prepare_pages
- * to avoid recursive lock
- */
- if (unlikely(iov_iter_fault_in_readable(&i, write_bytes))) {
- ret = -EFAULT;
- goto out;
- }
-
ret = prepare_pages(root, file, pages, num_pages,
pos, first_index, last_index,
write_bytes);
--
1.6.2.2
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Xin Zhong
2010-Dec-07 09:25 UTC
[PATCH] Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
This problem is found in meego testing:
http://bugs.meego.com/show_bug.cgi?id=6672
A file in btrfs is mmaped and the mmaped buffer is passed to pwrite to write to
the same page
of the same file. In btrfs_file_aio_write(), the pages is locked by
prepare_pages(). So when
btrfs_copy_from_user() is called, page fault happens and the same page needs to
be locked again
in filemap_fault(). The fix is to move iov_iter_fault_in_readable() before
prepage_pages() to make page
fault happen before pages are locked. And also disable page fault in critical
region in
btrfs_copy_from_user().
Signed-off-by: Xin Zhong <xin.zhong@intel.com>
---
fs/btrfs/file.c | 23 ++++++++++++++++++-----
1 files changed, 18 insertions(+), 5 deletions(-)
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index c1faded..805f2ee 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -57,11 +57,15 @@ static noinline int btrfs_copy_from_user(loff_t pos, int
num_pages,
PAGE_CACHE_SIZE - offset, write_bytes);
struct page *page = prepared_pages[pg];
again:
- if (unlikely(iov_iter_fault_in_readable(i, count)))
- return -EFAULT;
-
- /* Copy data from userspace to the current page */
- copied = iov_iter_copy_from_user(page, i, offset, count);
+ /*
+ * Copy data from userspace to the current page
+ *
+ * Disable pagefault to avoid recursive lock since
+ * the pages are already locked
+ */
+ pagefault_disable();
+ copied = iov_iter_copy_from_user_atomic(page, i, offset, count);
+ pagefault_enable();
/* Flush processor''s dcache for this page */
flush_dcache_page(page);
@@ -974,6 +978,15 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
if (ret)
goto out;
+ /*
+ * fault pages before locking them in prepare_pages
+ * to avoid recursive lock
+ */
+ if (unlikely(iov_iter_fault_in_readable(&i, write_bytes))) {
+ ret = -EFAULT;
+ goto out;
+ }
+
ret = prepare_pages(root, file, pages, num_pages,
pos, first_index, last_index,
write_bytes);
--
1.6.2.2
--
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Zhong, Xin
2010-Dec-07 09:34 UTC
RE: [PATCH] Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
The previous patch is not ok
(http://www.spinics.net/lists/linux-btrfs/msg07447.html). Please ignore it.
Thanks!
-----Original Message-----
From: Zhong, Xin
Sent: Tuesday, December 07, 2010 5:25 PM
To: linux-btrfs@vger.kernel.org
Cc: Zhong, Xin
Subject: [PATCH] Btrfs: pwrite blocked when writing from the mmaped buffer of
the same page
This problem is found in meego testing:
http://bugs.meego.com/show_bug.cgi?id=6672
A file in btrfs is mmaped and the mmaped buffer is passed to pwrite to write to
the same page
of the same file. In btrfs_file_aio_write(), the pages is locked by
prepare_pages(). So when
btrfs_copy_from_user() is called, page fault happens and the same page needs to
be locked again
in filemap_fault(). The fix is to move iov_iter_fault_in_readable() before
prepage_pages() to make page
fault happen before pages are locked. And also disable page fault in critical
region in
btrfs_copy_from_user().
Signed-off-by: Xin Zhong <xin.zhong@intel.com>
---
fs/btrfs/file.c | 23 ++++++++++++++++++-----
1 files changed, 18 insertions(+), 5 deletions(-)
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index c1faded..805f2ee 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -57,11 +57,15 @@ static noinline int btrfs_copy_from_user(loff_t pos, int
num_pages,
PAGE_CACHE_SIZE - offset, write_bytes);
struct page *page = prepared_pages[pg];
again:
- if (unlikely(iov_iter_fault_in_readable(i, count)))
- return -EFAULT;
-
- /* Copy data from userspace to the current page */
- copied = iov_iter_copy_from_user(page, i, offset, count);
+ /*
+ * Copy data from userspace to the current page
+ *
+ * Disable pagefault to avoid recursive lock since
+ * the pages are already locked
+ */
+ pagefault_disable();
+ copied = iov_iter_copy_from_user_atomic(page, i, offset, count);
+ pagefault_enable();
/* Flush processor''s dcache for this page */
flush_dcache_page(page);
@@ -974,6 +978,15 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
if (ret)
goto out;
+ /*
+ * fault pages before locking them in prepare_pages
+ * to avoid recursive lock
+ */
+ if (unlikely(iov_iter_fault_in_readable(&i, write_bytes))) {
+ ret = -EFAULT;
+ goto out;
+ }
+
ret = prepare_pages(root, file, pages, num_pages,
pos, first_index, last_index,
write_bytes);
--
1.6.2.2
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Zhong, Xin
2010-Dec-07 09:34 UTC
RE: [PATCH] Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
The other filesystems such as ext3 do not have this problem since they are using
generic_file_buffered_write(). And this problem is fixed back in 2007 for
generic_file_buffered_write():
http://lkml.org/lkml/2007/2/4/26
I am very new to btrfs. I am wondering why btrfs has it''s own write
routine?
Thanks!
-----Original Message-----
From: Zhong, Xin
Sent: Tuesday, December 07, 2010 5:25 PM
To: linux-btrfs@vger.kernel.org
Cc: Zhong, Xin
Subject: [PATCH] Btrfs: pwrite blocked when writing from the mmaped buffer of
the same page
This problem is found in meego testing:
http://bugs.meego.com/show_bug.cgi?id=6672
A file in btrfs is mmaped and the mmaped buffer is passed to pwrite to write to
the same page
of the same file. In btrfs_file_aio_write(), the pages is locked by
prepare_pages(). So when
btrfs_copy_from_user() is called, page fault happens and the same page needs to
be locked again
in filemap_fault(). The fix is to move iov_iter_fault_in_readable() before
prepage_pages() to make page
fault happen before pages are locked. And also disable page fault in critical
region in
btrfs_copy_from_user().
Signed-off-by: Xin Zhong <xin.zhong@intel.com>
---
fs/btrfs/file.c | 23 ++++++++++++++++++-----
1 files changed, 18 insertions(+), 5 deletions(-)
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index c1faded..805f2ee 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -57,11 +57,15 @@ static noinline int btrfs_copy_from_user(loff_t pos, int
num_pages,
PAGE_CACHE_SIZE - offset, write_bytes);
struct page *page = prepared_pages[pg];
again:
- if (unlikely(iov_iter_fault_in_readable(i, count)))
- return -EFAULT;
-
- /* Copy data from userspace to the current page */
- copied = iov_iter_copy_from_user(page, i, offset, count);
+ /*
+ * Copy data from userspace to the current page
+ *
+ * Disable pagefault to avoid recursive lock since
+ * the pages are already locked
+ */
+ pagefault_disable();
+ copied = iov_iter_copy_from_user_atomic(page, i, offset, count);
+ pagefault_enable();
/* Flush processor''s dcache for this page */
flush_dcache_page(page);
@@ -974,6 +978,15 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
if (ret)
goto out;
+ /*
+ * fault pages before locking them in prepare_pages
+ * to avoid recursive lock
+ */
+ if (unlikely(iov_iter_fault_in_readable(&i, write_bytes))) {
+ ret = -EFAULT;
+ goto out;
+ }
+
ret = prepare_pages(root, file, pages, num_pages,
pos, first_index, last_index,
write_bytes);
--
1.6.2.2
--
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Christoph Hellwig
2010-Dec-07 16:54 UTC
Re: [PATCH] Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
Care to write a xfstests test for this behaviour? -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Zhong, Xin
2010-Dec-13 08:26 UTC
RE: [PATCH] Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
I have sent my test case to xfs mailing list (No. 248). Please help to review it. Thanks! -----Original Message----- From: Christoph Hellwig [mailto:hch@infradead.org] Sent: Wednesday, December 08, 2010 12:55 AM To: Zhong, Xin Cc: linux-btrfs@vger.kernel.org Subject: Re: [PATCH] Btrfs: pwrite blocked when writing from the mmaped buffer of the same page Care to write a xfstests test for this behaviour? -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Chris Mason
2010-Dec-14 01:35 UTC
RE: [PATCH] Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
Excerpts from Zhong, Xin''s message of 2010-12-13 03:26:04 -0500:> I have sent my test case to xfs mailing list (No. 248). > Please help to review it. Thanks!You btrfs patch is now in the master branch of the btrfs unstable tree. Thanks! -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Zhong, Xin
2010-Dec-14 02:44 UTC
RE: [PATCH] Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
Chris, thanks a lot for your quick response. Thanks to Zheng Yan too for his careful review. -----Original Message----- From: Chris Mason [mailto:chris.mason@oracle.com] Sent: Tuesday, December 14, 2010 9:36 AM To: Zhong, Xin Cc: Christoph Hellwig; linux-btrfs@vger.kernel.org Subject: RE: [PATCH] Btrfs: pwrite blocked when writing from the mmaped buffer of the same page Excerpts from Zhong, Xin's message of 2010-12-13 03:26:04 -0500:> I have sent my test case to xfs mailing list (No. 248). > Please help to review it. Thanks!You btrfs patch is now in the master branch of the btrfs unstable tree. Thanks! -chris NrybXǧv^){.n+{n߲)w*jgݢj/zޖ2ޙ&)ߡaGhj:+vw٥
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