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Date: Mon, 22 Jun 2009 09:58:18 +0100
From: David Howells <dhowells@...hat.com>
To: Linux filesystem caching discussion list
<linux-cachefs@...hat.com>
Cc: dhowells@...hat.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Linux-cachefs] CacheFiles: Readpage failed on backing file
Christian Kujau <lists@...dbynature.de> wrote:
> [ 399.332346] [<ffffffff810da03a>] ? ext3_truncate+0x26a/0x9e0
Can you try the attached patch, please?
David
---
From: David Howells <dhowells@...hat.com>
Subject: [PATCH] CacheFiles: Don't write a full page if there's only a partial page to cache
cachefiles_write_page() writes a full page to the backing file for the last
page of the netfs file, even if the netfs file's last page is only a partial
page.
This causes the EOF on the backing file to be extended beyond the EOF of the
netfs, and thus the backing file will be truncated by cachefiles_attr_changed()
called from cachefiles_lookup_object().
So we need to limit the write we make to the backing file on that last page
such that it doesn't push the EOF too far.
Also, if a backing file that has a partial page at the end is expanded, we
discard the partial page and refetch it on the basis that we then have a hole
in the file with invalid data, and should the power go out... A better way to
deal with this could be to record a note that the partial page contains invalid
data until the correct data is written into it.
This isn't a problem for netfs's that discard the whole backing file if the
file size changes (such as NFS).
Signed-off-by: David Howells <dhowells@...hat.com>
---
fs/cachefiles/interface.c | 20 +++++++++++++++++---
fs/cachefiles/rdwr.c | 23 +++++++++++++++++++----
include/linux/fscache-cache.h | 3 +++
3 files changed, 39 insertions(+), 7 deletions(-)
diff --git a/fs/cachefiles/interface.c b/fs/cachefiles/interface.c
index 431accd..919a7b6 100644
--- a/fs/cachefiles/interface.c
+++ b/fs/cachefiles/interface.c
@@ -403,12 +403,26 @@ static int cachefiles_attr_changed(struct fscache_object *_object)
if (oi_size == ni_size)
return 0;
- newattrs.ia_size = ni_size;
- newattrs.ia_valid = ATTR_SIZE;
-
cachefiles_begin_secure(cache, &saved_cred);
mutex_lock(&object->backer->d_inode->i_mutex);
+
+ /* if there's an extension to a partial page at the end of the backing
+ * file, we need to discard the partial page so that we pick up new
+ * data after it */
+ if (oi_size & ~PAGE_MASK && ni_size > oi_size) {
+ _debug("discard tail %llx", oi_size);
+ newattrs.ia_valid = ATTR_SIZE;
+ newattrs.ia_size = oi_size & PAGE_MASK;
+ ret = notify_change(object->backer, &newattrs);
+ if (ret < 0)
+ goto truncate_failed;
+ }
+
+ newattrs.ia_valid = ATTR_SIZE;
+ newattrs.ia_size = ni_size;
ret = notify_change(object->backer, &newattrs);
+
+truncate_failed:
mutex_unlock(&object->backer->d_inode->i_mutex);
cachefiles_end_secure(cache, saved_cred);
diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c
index a69787e..86639c1 100644
--- a/fs/cachefiles/rdwr.c
+++ b/fs/cachefiles/rdwr.c
@@ -801,7 +801,8 @@ int cachefiles_write_page(struct fscache_storage *op, struct page *page)
struct cachefiles_cache *cache;
mm_segment_t old_fs;
struct file *file;
- loff_t pos;
+ loff_t pos, eof;
+ size_t len;
void *data;
int ret;
@@ -835,15 +836,29 @@ int cachefiles_write_page(struct fscache_storage *op, struct page *page)
ret = -EIO;
if (file->f_op->write) {
pos = (loff_t) page->index << PAGE_SHIFT;
+
+ /* we mustn't write more data than we have, so we have
+ * to beware of a partial page at EOF */
+ eof = object->fscache.store_limit_l;
+ len = PAGE_SIZE;
+ if (eof & ~PAGE_MASK) {
+ ASSERTCMP(pos, <, eof);
+ if (eof - pos < PAGE_SIZE) {
+ _debug("cut short %llx to %llx",
+ pos, eof);
+ len = eof - pos;
+ ASSERTCMP(pos + len, ==, eof);
+ }
+ }
+
data = kmap(page);
old_fs = get_fs();
set_fs(KERNEL_DS);
ret = file->f_op->write(
- file, (const void __user *) data, PAGE_SIZE,
- &pos);
+ file, (const void __user *) data, len, &pos);
set_fs(old_fs);
kunmap(page);
- if (ret != PAGE_SIZE)
+ if (ret != len)
ret = -EIO;
}
fput(file);
diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index 84d3532..97229be 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -374,6 +374,7 @@ struct fscache_object {
struct list_head dep_link; /* link in parent's dependents list */
struct list_head pending_ops; /* unstarted operations on this object */
pgoff_t store_limit; /* current storage limit */
+ loff_t store_limit_l; /* current storage limit */
};
extern const char *fscache_object_states[];
@@ -414,6 +415,7 @@ void fscache_object_init(struct fscache_object *object,
object->events = object->event_mask = 0;
object->flags = 0;
object->store_limit = 0;
+ object->store_limit_l = 0;
object->cache = cache;
object->cookie = cookie;
object->parent = NULL;
@@ -460,6 +462,7 @@ static inline void fscache_object_lookup_error(struct fscache_object *object)
static inline
void fscache_set_store_limit(struct fscache_object *object, loff_t i_size)
{
+ object->store_limit_l = i_size;
object->store_limit = i_size >> PAGE_SHIFT;
if (i_size & ~PAGE_MASK)
object->store_limit++;
--
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