The patch titled
mm: pagecache write deadlocks
has been removed from the -mm tree. Its filename is
mm-pagecache-write-deadlocks.patch
This patch was dropped because it is obsolete
------------------------------------------------------
Subject: mm: pagecache write deadlocks
From: Nick Piggin <npiggin@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
fs/buffer.c | 41 +++++++------------------
fs/libfs.c | 49 +++++++++++++++++-------------
mm/filemap.c | 80 ++++++++++++++++++++++++++-----------------------
mm/filemap.h | 74 +++++++++++++++++++++++++++++----------------
4 files changed, 134 insertions(+), 110 deletions(-)
diff -puN fs/buffer.c~mm-pagecache-write-deadlocks fs/buffer.c
--- a/fs/buffer.c~mm-pagecache-write-deadlocks
+++ a/fs/buffer.c
@@ -1874,6 +1874,9 @@ static int __block_commit_write(struct i
unsigned blocksize;
struct buffer_head *bh, *head;
+ if (from == to)
+ return 0;
+
blocksize = 1 << inode->i_blkbits;
for(bh = head = page_buffers(page), block_start = 0;
@@ -2335,17 +2338,6 @@ int nobh_prepare_write(struct page *page
if (is_mapped_to_disk)
SetPageMappedToDisk(page);
- SetPageUptodate(page);
-
- /*
- * Setting the page dirty here isn't necessary for the prepare_write
- * function - commit_write will do that. But if/when this function is
- * used within the pagefault handler to ensure that all mmapped pages
- * have backing space in the filesystem, we will need to dirty the page
- * if its contents were altered.
- */
- if (dirtied_it)
- set_page_dirty(page);
return 0;
@@ -2354,17 +2346,6 @@ failed:
if (read_bh[i])
free_buffer_head(read_bh[i]);
}
-
- /*
- * Error recovery is pretty slack. Clear the page and mark it dirty
- * so we'll later zero out any blocks which _were_ allocated.
- */
- kaddr = kmap_atomic(page, KM_USER0);
- memset(kaddr, 0, PAGE_CACHE_SIZE);
- flush_dcache_page(page);
- kunmap_atomic(kaddr, KM_USER0);
- SetPageUptodate(page);
- set_page_dirty(page);
return ret;
}
EXPORT_SYMBOL(nobh_prepare_write);
@@ -2372,13 +2353,16 @@ EXPORT_SYMBOL(nobh_prepare_write);
int nobh_commit_write(struct file *file, struct page *page,
unsigned from, unsigned to)
{
- struct inode *inode = page->mapping->host;
- loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
+ if (to > from) {
+ struct inode *inode = page->mapping->host;
+ loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
- set_page_dirty(page);
- if (pos > inode->i_size) {
- i_size_write(inode, pos);
- mark_inode_dirty(inode);
+ SetPageUptodate(page);
+ set_page_dirty(page);
+ if (pos > inode->i_size) {
+ i_size_write(inode, pos);
+ mark_inode_dirty(inode);
+ }
}
return 0;
}
@@ -2469,6 +2453,7 @@ int nobh_truncate_page(struct address_sp
memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
flush_dcache_page(page);
kunmap_atomic(kaddr, KM_USER0);
+ SetPageUptodate(page);
set_page_dirty(page);
}
unlock_page(page);
diff -puN fs/libfs.c~mm-pagecache-write-deadlocks fs/libfs.c
--- a/fs/libfs.c~mm-pagecache-write-deadlocks
+++ a/fs/libfs.c
@@ -327,32 +327,41 @@ int simple_readpage(struct file *file, s
int simple_prepare_write(struct file *file, struct page *page,
unsigned from, unsigned to)
{
- if (!PageUptodate(page)) {
- if (to - from != PAGE_CACHE_SIZE) {
- void *kaddr = kmap_atomic(page, KM_USER0);
- memset(kaddr, 0, from);
- memset(kaddr + to, 0, PAGE_CACHE_SIZE - to);
- flush_dcache_page(page);
- kunmap_atomic(kaddr, KM_USER0);
- }
- SetPageUptodate(page);
+ if (PageUptodate(page))
+ return 0;
+
+ ClearPageError(page);
+ if (to - from != PAGE_CACHE_SIZE) {
+ struct address_space *mapping = page->mapping;
+ int status = mapping->a_ops->readpage(file, page);
+ /* unlocked the page so must retry */
+ /* XXX: AOP_TRUNCATED_PAGE is a horrible name */
+ if (!status)
+ status = AOP_TRUNCATED_PAGE;
+ return status;
}
+
return 0;
}
int simple_commit_write(struct file *file, struct page *page,
- unsigned offset, unsigned to)
+ unsigned from, unsigned to)
{
- struct inode *inode = page->mapping->host;
- loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
-
- /*
- * No need to use i_size_read() here, the i_size
- * cannot change under us because we hold the i_mutex.
- */
- if (pos > inode->i_size)
- i_size_write(inode, pos);
- set_page_dirty(page);
+ if (to > from) {
+ struct inode *inode = page->mapping->host;
+ loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
+
+ if (to - from == PAGE_CACHE_SIZE)
+ SetPageUptodate(page);
+ /*
+ * No need to use i_size_read() here, the i_size
+ * cannot change under us because we hold the i_mutex.
+ */
+ if (pos > inode->i_size)
+ i_size_write(inode, pos);
+ /* XXX: why no mark_inode_dirty? */
+ set_page_dirty(page);
+ }
return 0;
}
diff -puN mm/filemap.c~mm-pagecache-write-deadlocks mm/filemap.c
--- a/mm/filemap.c~mm-pagecache-write-deadlocks
+++ a/mm/filemap.c
@@ -2102,10 +2102,9 @@ generic_file_buffered_write(struct kiocb
bytes = min(cur_iov->iov_len - iov_offset, bytes);
/*
- * Bring in the user page that we will copy from _first_.
- * Otherwise there's a nasty deadlock on copying from the
- * same page as we're writing to, without it being marked
- * up-to-date.
+ * Bring in the user page that we will copy from _first_, this
+ * minimises the chance we have to break into the slowpath
+ * below.
*/
fault_in_pages_readable(buf, bytes);
@@ -2117,8 +2116,6 @@ generic_file_buffered_write(struct kiocb
status = a_ops->prepare_write(file, page, offset, offset+bytes);
if (unlikely(status)) {
- loff_t isize = i_size_read(inode);
-
if (status != AOP_TRUNCATED_PAGE)
unlock_page(page);
page_cache_release(page);
@@ -2126,52 +2123,63 @@ generic_file_buffered_write(struct kiocb
continue;
/*
* prepare_write() may have instantiated a few blocks
- * outside i_size. Trim these off again.
+ * outside i_size. Trim these off again. Don't need
+ * i_size_read because we hold i_mutex.
*/
- if (pos + bytes > isize)
- vmtruncate(inode, isize);
+ if (pos + bytes > inode->i_size)
+ vmtruncate(inode, inode->i_size);
break;
}
+
+ /*
+ * Must not enter the pagefault handler here, because we hold
+ * the page lock, so we might recursively deadlock on the same
+ * lock, or get an ABBA deadlock against a different lock, or
+ * against the mmap_sem (which nests outside the page lock).
+ * So increment preempt count, and use _atomic usercopies.
+ */
+ inc_preempt_count();
if (likely(nr_segs == 1))
- copied = filemap_copy_from_user(page, offset,
+ copied = filemap_copy_from_user_atomic(page, offset,
buf, bytes);
else
- copied = filemap_copy_from_user_iovec(page, offset,
- cur_iov, iov_offset, bytes);
+ copied = filemap_copy_from_user_iovec_atomic(page,
+ offset, cur_iov, iov_offset,
+ bytes);
+ dec_preempt_count();
+ if (unlikely(copied != bytes))
+ copied = 0;
+
flush_dcache_page(page);
- status = a_ops->commit_write(file, page, offset, offset+bytes);
+ status = a_ops->commit_write(file, page, offset, offset+copied);
if (status == AOP_TRUNCATED_PAGE) {
page_cache_release(page);
continue;
}
- if (likely(copied > 0)) {
- if (!status)
- status = copied;
-
- if (status >= 0) {
- written += status;
- count -= status;
- pos += status;
- buf += status;
- if (unlikely(nr_segs > 1)) {
- filemap_set_next_iovec(&cur_iov,
- &iov_offset, status);
- if (count)
- buf = cur_iov->iov_base +
- iov_offset;
- } else {
- iov_offset += status;
- }
- }
- }
- if (unlikely(copied != bytes))
- if (status >= 0)
- status = -EFAULT;
unlock_page(page);
mark_page_accessed(page);
page_cache_release(page);
+
if (status < 0)
break;
+ if (likely(copied == bytes)) {
+ written += copied;
+ count -= copied;
+ pos += copied;
+ buf += copied;
+ if (unlikely(nr_segs > 1)) {
+ filemap_set_next_iovec(&cur_iov,
+ &iov_offset, copied);
+ if (count)
+ buf = cur_iov->iov_base + iov_offset;
+ } else {
+ iov_offset += copied;
+ }
+#ifdef CONFIG_DEBUG_VM
+ } else {
+ fault_in_pages_readable(buf, bytes);
+#endif
+ }
balance_dirty_pages_ratelimited(mapping);
cond_resched();
} while (count);
diff -puN mm/filemap.h~mm-pagecache-write-deadlocks mm/filemap.h
--- a/mm/filemap.h~mm-pagecache-write-deadlocks
+++ a/mm/filemap.h
@@ -22,19 +22,19 @@ __filemap_copy_from_user_iovec_inatomic(
/*
* Copy as much as we can into the page and return the number of bytes which
- * were sucessfully copied. If a fault is encountered then clear the page
- * out to (offset+bytes) and return the number of bytes which were copied.
+ * were sucessfully copied. If a fault is encountered then return the number of
+ * bytes which were copied.
*
- * NOTE: For this to work reliably we really want copy_from_user_inatomic_nocache
- * to *NOT* zero any tail of the buffer that it failed to copy. If it does,
- * and if the following non-atomic copy succeeds, then there is a small window
- * where the target page contains neither the data before the write, nor the
- * data after the write (it contains zero). A read at this time will see
- * data that is inconsistent with any ordering of the read and the write.
- * (This has been detected in practice).
+ * NOTE: For this to work reliably we really want
+ * copy_from_user_inatomic_nocache to *NOT* zero any tail of the buffer that it
+ * failed to copy. If it does, and if the following non-atomic copy succeeds,
+ * then there is a small window where the target page contains neither the data
+ * before the write, nor the data after the write (it contains zero). A read at
+ * this time will see data that is inconsistent with any ordering of the read
+ * and the write. (This has been detected in practice).
*/
static inline size_t
-filemap_copy_from_user(struct page *page, unsigned long offset,
+filemap_copy_from_user_atomic(struct page *page, unsigned long offset,
const char __user *buf, unsigned bytes)
{
char *kaddr;
@@ -44,23 +44,32 @@ filemap_copy_from_user(struct page *page
left = __copy_from_user_inatomic_nocache(kaddr + offset, buf, bytes);
kunmap_atomic(kaddr, KM_USER0);
- if (left != 0) {
- /* Do it the slow way */
- kaddr = kmap(page);
- left = __copy_from_user_nocache(kaddr + offset, buf, bytes);
- kunmap(page);
- }
+ return bytes - left;
+}
+
+static inline size_t
+filemap_copy_from_user_nonatomic(struct page *page, unsigned long offset,
+ const char __user *buf, unsigned bytes)
+{
+ char *kaddr;
+ int left;
+
+ kaddr = kmap(page);
+ left = __copy_from_user_nocache(kaddr + offset, buf, bytes);
+ kunmap(page);
+
return bytes - left;
}
/*
- * This has the same sideeffects and return value as filemap_copy_from_user().
+ * This has the same sideeffects and return value as
+ * filemap_copy_from_user_atomic().
* The difference is that on a fault we need to memset the remainder of the
* page (out to offset+bytes), to emulate filemap_copy_from_user()'s
* single-segment behaviour.
*/
static inline size_t
-filemap_copy_from_user_iovec(struct page *page, unsigned long offset,
+filemap_copy_from_user_iovec_atomic(struct page *page, unsigned long offset,
const struct iovec *iov, size_t base, size_t bytes)
{
char *kaddr;
@@ -70,14 +79,27 @@ filemap_copy_from_user_iovec(struct page
copied = __filemap_copy_from_user_iovec_inatomic(kaddr + offset, iov,
base, bytes);
kunmap_atomic(kaddr, KM_USER0);
- if (copied != bytes) {
- kaddr = kmap(page);
- copied = __filemap_copy_from_user_iovec_inatomic(kaddr + offset, iov,
- base, bytes);
- if (bytes - copied)
- memset(kaddr + offset + copied, 0, bytes - copied);
- kunmap(page);
- }
+ return copied;
+}
+
+/*
+ * This has the same sideeffects and return value as
+ * filemap_copy_from_user_nonatomic().
+ * The difference is that on a fault we need to memset the remainder of the
+ * page (out to offset+bytes), to emulate filemap_copy_from_user_nonatomic()'s
+ * single-segment behaviour.
+ */
+static inline size_t
+filemap_copy_from_user_iovec_nonatomic(struct page *page, unsigned long offset,
+ const struct iovec *iov, size_t base, size_t bytes)
+{
+ char *kaddr;
+ size_t copied;
+
+ kaddr = kmap(page);
+ copied = __filemap_copy_from_user_iovec_inatomic(kaddr + offset, iov,
+ base, bytes);
+ kunmap(page);
return copied;
}
_
Patches currently in -mm which might be from npiggin@xxxxxxx are
mm-comment-mmap_sem--lock_page-lockorder.patch
mm-only-mm-debug-write-deadlocks.patch
mm-fix-pagecache-write-deadlocks.patch
mm-pagecache-write-deadlocks.patch
oom-dont-kill-unkillable-children-or-siblings.patch
oom-cleanup-messages.patch
oom-less-memdie.patch
mm-incorrect-vm_fault_oom-returns-from-drivers.patch
mm-add-arch_alloc_page.patch
radix-tree-rcu-lockless-readside.patch
-
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