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Fix write trans/page lock inversions

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scoutfs_write_begin() was riddled with lock ordering and cleanup bugs:

 - blocked holding the trans with the page lock held
 - dirtied the inode with the page lock held
 - didn't release the trans on error
 - tried to double unlock and release pages on readpage error

We fix all this up by reordering things so we hold the trans, dirty the
inode, then work pages all while more carefully cleaning up.

Signed-off-by: Zach Brown <zab@versity.com>
Reviewed-by: Mark Fasheh <mfasheh@versity.com>
This commit is contained in:
Zach Brown
2016-11-09 12:40:54 -08:00
parent f54f61f064
commit 256166db32
1 changed files with 31 additions and 36 deletions
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67
kmod/src/filerw.c
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@@ -582,41 +582,9 @@ static int scoutfs_write_begin(struct file *file,
struct page *page;
int ret;
retry:
page = grab_cache_page_write_begin(mapping, index, flags);
if (!page)
return -ENOMEM;
trace_printk(PGF" pos %llu len %u\n", PGA(page), (u64)pos, len);
/*
* read in the page if we're going to be dirtying part of the
* page. readpage catches when this is a read past i_size or
* from a hole and zeros the buffer.
*/
if (!PageUptodate(page) && !IS_ALIGNED(pos | len, SCOUTFS_BLOCK_SIZE)) {
ClearPageError(page);
ret = scoutfs_readpage(NULL, page);
if (ret) {
page_cache_release(page);
goto out;
}
wait_on_page_locked(page);
if (!PageUptodate(page)) {
page_cache_release(page);
ret = -EIO;
goto out;
}
/* let grabbing deal with weird page states */
page_cache_release(page);
goto retry;
}
ret = scoutfs_hold_trans(sb);
if (ret)
goto out;
return ret;
/* can't re-enter fs, have trans */
flags |= AOP_FLAG_NOFS;
@@ -626,14 +594,38 @@ retry:
if (ret)
goto out;
retry:
page = grab_cache_page_write_begin(mapping, index, flags);
if (!page) {
ret = -ENOMEM;
goto out;
}
/*
* read in the page if we're going to be dirtying part of the
* page. readpage catches when this is a read past i_size or
* from a hole and zeros the buffer. We try to grab the page
* again to let it deal with locking and races.
*/
if (!PageUptodate(page) && !IS_ALIGNED(pos | len, SCOUTFS_BLOCK_SIZE)) {
ClearPageError(page);
ret = scoutfs_readpage(file, page);
if (!ret) {
wait_on_page_locked(page);
if (!PageUptodate(page))
ret = -EIO;
}
page_cache_release(page);
if (ret)
goto out;
goto retry;
}
/* make sure our get_block gets a chance to alloc */
clear_mapped_page_buffers(page);
ret = __block_write_begin(page, pos, len,
scoutfs_write_begin_get_block);
out:
trace_printk(PGF" pos %llu len %u ret %d\n",
PGA(page), (u64)pos, len, ret);
if (ret < 0) {
/* XXX handle truncating? */
unlock_page(page);
@@ -642,6 +634,9 @@ out:
}
*pagep = page;
out:
if (ret)
scoutfs_release_trans(sb);
return ret;
}