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authorChris Mason <chris.mason@oracle.com>2011-02-28 09:52:08 -0500
committerChris Mason <chris.mason@oracle.com>2011-03-07 10:42:27 -0500
commitb1bf862e9dad431175a1174379476299dbfdc017 (patch)
treea53811b2112fbe2a0106e3ac051fffc63872d317 /fs
parentec29ed5b407d618a8128f5942aade9e1758aa14b (diff)
downloadlinux-linaro-stable-b1bf862e9dad431175a1174379476299dbfdc017.tar.gz
Btrfs: fix regressions in copy_from_user handling
Commit 914ee295af418e936ec20a08c1663eaabe4cd07a fixed deadlocks in btrfs_file_write where we would catch page faults on pages we had locked. But, there were a few problems: 1) The x86-32 iov_iter_copy_from_user_atomic code always fails to copy data when the amount to copy is more than 4K and the offset to start copying from is not page aligned. The result was btrfs_file_write looping forever retrying the iov_iter_copy_from_user_atomic We deal with this by changing btrfs_file_write to drop down to single page copies when iov_iter_copy_from_user_atomic starts returning failure. 2) The btrfs_file_write code was leaking delalloc reservations when iov_iter_copy_from_user_atomic returned zero. The looping above would result in the entire filesystem running out of delalloc reservations and constantly trying to flush things to disk. 3) btrfs_file_write will lock down page cache pages, make sure any writeback is finished, do the copy_from_user and then release them. Before the loop runs we check the first and last pages in the write to see if they are only being partially modified. If the start or end of the write isn't aligned, we make sure the corresponding pages are up to date so that we don't introduce garbage into the file. With the copy_from_user changes, we're allowing the VM to reclaim the pages after a partial update from copy_from_user, but we're not making sure the page cache page is up to date when we loop around to resume the write. We deal with this by pushing the up to date checks down into the page prep code. This fits better with how the rest of file_write works. Signed-off-by: Chris Mason <chris.mason@oracle.com> Reported-by: Mitch Harder <mitch.harder@sabayonlinux.org> cc: stable@kernel.org
Diffstat (limited to 'fs')
-rw-r--r--fs/btrfs/file.c101
1 files changed, 59 insertions, 42 deletions
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 65338a1d14ad..13664b315fe2 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -762,6 +762,27 @@ out:
}
/*
+ * on error we return an unlocked page and the error value
+ * on success we return a locked page and 0
+ */
+static int prepare_uptodate_page(struct page *page, u64 pos)
+{
+ int ret = 0;
+
+ if ((pos & (PAGE_CACHE_SIZE - 1)) && !PageUptodate(page)) {
+ ret = btrfs_readpage(NULL, page);
+ if (ret)
+ return ret;
+ lock_page(page);
+ if (!PageUptodate(page)) {
+ unlock_page(page);
+ return -EIO;
+ }
+ }
+ return 0;
+}
+
+/*
* this gets pages into the page cache and locks them down, it also properly
* waits for data=ordered extents to finish before allowing the pages to be
* modified.
@@ -776,6 +797,7 @@ static noinline int prepare_pages(struct btrfs_root *root, struct file *file,
unsigned long index = pos >> PAGE_CACHE_SHIFT;
struct inode *inode = fdentry(file)->d_inode;
int err = 0;
+ int faili = 0;
u64 start_pos;
u64 last_pos;
@@ -793,15 +815,24 @@ again:
for (i = 0; i < num_pages; i++) {
pages[i] = grab_cache_page(inode->i_mapping, index + i);
if (!pages[i]) {
- int c;
- for (c = i - 1; c >= 0; c--) {
- unlock_page(pages[c]);
- page_cache_release(pages[c]);
- }
- return -ENOMEM;
+ faili = i - 1;
+ err = -ENOMEM;
+ goto fail;
+ }
+
+ if (i == 0)
+ err = prepare_uptodate_page(pages[i], pos);
+ if (i == num_pages - 1)
+ err = prepare_uptodate_page(pages[i],
+ pos + write_bytes);
+ if (err) {
+ page_cache_release(pages[i]);
+ faili = i - 1;
+ goto fail;
}
wait_on_page_writeback(pages[i]);
}
+ err = 0;
if (start_pos < inode->i_size) {
struct btrfs_ordered_extent *ordered;
lock_extent_bits(&BTRFS_I(inode)->io_tree,
@@ -841,6 +872,14 @@ again:
WARN_ON(!PageLocked(pages[i]));
}
return 0;
+fail:
+ while (faili >= 0) {
+ unlock_page(pages[faili]);
+ page_cache_release(pages[faili]);
+ faili--;
+ }
+ return err;
+
}
static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
@@ -850,7 +889,6 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
struct file *file = iocb->ki_filp;
struct inode *inode = fdentry(file)->d_inode;
struct btrfs_root *root = BTRFS_I(inode)->root;
- struct page *pinned[2];
struct page **pages = NULL;
struct iov_iter i;
loff_t *ppos = &iocb->ki_pos;
@@ -871,9 +909,6 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
will_write = ((file->f_flags & O_DSYNC) || IS_SYNC(inode) ||
(file->f_flags & O_DIRECT));
- pinned[0] = NULL;
- pinned[1] = NULL;
-
start_pos = pos;
vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
@@ -961,32 +996,6 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
first_index = pos >> PAGE_CACHE_SHIFT;
last_index = (pos + iov_iter_count(&i)) >> PAGE_CACHE_SHIFT;
- /*
- * there are lots of better ways to do this, but this code
- * makes sure the first and last page in the file range are
- * up to date and ready for cow
- */
- if ((pos & (PAGE_CACHE_SIZE - 1))) {
- pinned[0] = grab_cache_page(inode->i_mapping, first_index);
- if (!PageUptodate(pinned[0])) {
- ret = btrfs_readpage(NULL, pinned[0]);
- BUG_ON(ret);
- wait_on_page_locked(pinned[0]);
- } else {
- unlock_page(pinned[0]);
- }
- }
- if ((pos + iov_iter_count(&i)) & (PAGE_CACHE_SIZE - 1)) {
- pinned[1] = grab_cache_page(inode->i_mapping, last_index);
- if (!PageUptodate(pinned[1])) {
- ret = btrfs_readpage(NULL, pinned[1]);
- BUG_ON(ret);
- wait_on_page_locked(pinned[1]);
- } else {
- unlock_page(pinned[1]);
- }
- }
-
while (iov_iter_count(&i) > 0) {
size_t offset = pos & (PAGE_CACHE_SIZE - 1);
size_t write_bytes = min(iov_iter_count(&i),
@@ -1023,8 +1032,20 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
copied = btrfs_copy_from_user(pos, num_pages,
write_bytes, pages, &i);
- dirty_pages = (copied + offset + PAGE_CACHE_SIZE - 1) >>
- PAGE_CACHE_SHIFT;
+
+ /*
+ * if we have trouble faulting in the pages, fall
+ * back to one page at a time
+ */
+ if (copied < write_bytes)
+ nrptrs = 1;
+
+ if (copied == 0)
+ dirty_pages = 0;
+ else
+ dirty_pages = (copied + offset +
+ PAGE_CACHE_SIZE - 1) >>
+ PAGE_CACHE_SHIFT;
if (num_pages > dirty_pages) {
if (copied > 0)
@@ -1068,10 +1089,6 @@ out:
err = ret;
kfree(pages);
- if (pinned[0])
- page_cache_release(pinned[0]);
- if (pinned[1])
- page_cache_release(pinned[1]);
*ppos = pos;
/*