[PATCH 24/28] CacheFiles: Handle truncate unlocking the page we'rereading
From: David Howells
Date: Thu Nov 19 2009 - 12:22:56 EST
Handle truncate unlocking the page we're attempting to read from the backing
device before the read has completed.
This was causing reports like the following to occur:
Pid: 4765, comm: kslowd Not tainted 2.6.30.1 #1
Call Trace:
[<ffffffffa0331d7a>] ? cachefiles_read_waiter+0xd9/0x147 [cachefiles]
[<ffffffff804b74bd>] ? __wait_on_bit+0x60/0x6f
[<ffffffff8022bbbb>] ? __wake_up_common+0x3f/0x71
[<ffffffff8022cc32>] ? __wake_up+0x30/0x44
[<ffffffff8024a41f>] ? __wake_up_bit+0x28/0x2d
[<ffffffffa003a793>] ? ext3_truncate+0x4d7/0x8ed [ext3]
[<ffffffff80281f90>] ? pagevec_lookup+0x17/0x1f
[<ffffffff8028c2ff>] ? unmap_mapping_range+0x59/0x1ff
[<ffffffff8022cc32>] ? __wake_up+0x30/0x44
[<ffffffff8028e286>] ? vmtruncate+0xc2/0xe2
[<ffffffff802b82cf>] ? inode_setattr+0x22/0x10a
[<ffffffffa003baa5>] ? ext3_setattr+0x17b/0x1e6 [ext3]
[<ffffffff802b853d>] ? notify_change+0x186/0x2c9
[<ffffffffa032d9de>] ? cachefiles_attr_changed+0x133/0x1cd [cachefiles]
[<ffffffffa032df7f>] ? cachefiles_lookup_object+0xcf/0x12a [cachefiles]
[<ffffffffa0318165>] ? fscache_lookup_object+0x110/0x122 [fscache]
[<ffffffffa03188c3>] ? fscache_object_slow_work_execute+0x590/0x6bc
[fscache]
[<ffffffff80278f82>] ? slow_work_thread+0x285/0x43a
[<ffffffff8024a446>] ? autoremove_wake_function+0x0/0x2e
[<ffffffff80278cfd>] ? slow_work_thread+0x0/0x43a
[<ffffffff8024a317>] ? kthread+0x54/0x81
[<ffffffff8020c93a>] ? child_rip+0xa/0x20
[<ffffffff8024a2c3>] ? kthread+0x0/0x81
[<ffffffff8020c930>] ? child_rip+0x0/0x20
CacheFiles: I/O Error: Readpage failed on backing file 200000000000810
FS-Cache: Cache cachefiles stopped due to I/O error
Reported-by: Christian Kujau <lists@xxxxxxxxxxxxxxx>
Reported-by: Takashi Iwai <tiwai@xxxxxxx>
Reported-by: Duc Le Minh <duclm.vn@xxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---
fs/cachefiles/rdwr.c | 99 +++++++++++++++++++++++++++++++++++++++++++++++---
1 files changed, 93 insertions(+), 6 deletions(-)
diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c
index 5a84fd7..1d83325 100644
--- a/fs/cachefiles/rdwr.c
+++ b/fs/cachefiles/rdwr.c
@@ -40,8 +40,10 @@ static int cachefiles_read_waiter(wait_queue_t *wait, unsigned mode,
_debug("--- monitor %p %lx ---", page, page->flags);
- if (!PageUptodate(page) && !PageError(page))
- dump_stack();
+ if (!PageUptodate(page) && !PageError(page)) {
+ /* unlocked, not uptodate and not erronous? */
+ _debug("page probably truncated");
+ }
/* remove from the waitqueue */
list_del(&wait->task_list);
@@ -61,6 +63,84 @@ static int cachefiles_read_waiter(wait_queue_t *wait, unsigned mode,
}
/*
+ * handle a probably truncated page
+ * - check to see if the page is still relevant and reissue the read if
+ * possible
+ * - return -EIO on error, -ENODATA if the page is gone, -EINPROGRESS if we
+ * must wait again and 0 if successful
+ */
+static int cachefiles_read_reissue(struct cachefiles_object *object,
+ struct cachefiles_one_read *monitor)
+{
+ struct address_space *bmapping = object->backer->d_inode->i_mapping;
+ struct page *backpage = monitor->back_page, *backpage2;
+ int ret;
+
+ kenter("{ino=%lx},{%lx,%lx}",
+ object->backer->d_inode->i_ino,
+ backpage->index, backpage->flags);
+
+ /* skip if the page was truncated away completely */
+ if (backpage->mapping != bmapping) {
+ kleave(" = -ENODATA [mapping]");
+ return -ENODATA;
+ }
+
+ backpage2 = find_get_page(bmapping, backpage->index);
+ if (!backpage2) {
+ kleave(" = -ENODATA [gone]");
+ return -ENODATA;
+ }
+
+ if (backpage != backpage2) {
+ put_page(backpage2);
+ kleave(" = -ENODATA [different]");
+ return -ENODATA;
+ }
+
+ /* the page is still there and we already have a ref on it, so we don't
+ * need a second */
+ put_page(backpage2);
+
+ INIT_LIST_HEAD(&monitor->op_link);
+ add_page_wait_queue(backpage, &monitor->monitor);
+
+ if (trylock_page(backpage)) {
+ ret = -EIO;
+ if (PageError(backpage))
+ goto unlock_discard;
+ ret = 0;
+ if (PageUptodate(backpage))
+ goto unlock_discard;
+
+ kdebug("reissue read");
+ ret = bmapping->a_ops->readpage(NULL, backpage);
+ if (ret < 0)
+ goto unlock_discard;
+ }
+
+ /* but the page may have been read before the monitor was installed, so
+ * the monitor may miss the event - so we have to ensure that we do get
+ * one in such a case */
+ if (trylock_page(backpage)) {
+ _debug("jumpstart %p {%lx}", backpage, backpage->flags);
+ unlock_page(backpage);
+ }
+
+ /* it'll reappear on the todo list */
+ kleave(" = -EINPROGRESS");
+ return -EINPROGRESS;
+
+unlock_discard:
+ unlock_page(backpage);
+ spin_lock_irq(&object->work_lock);
+ list_del(&monitor->op_link);
+ spin_unlock_irq(&object->work_lock);
+ kleave(" = %d", ret);
+ return ret;
+}
+
+/*
* copy data from backing pages to netfs pages to complete a read operation
* - driven by FS-Cache's thread pool
*/
@@ -92,20 +172,26 @@ static void cachefiles_read_copier(struct fscache_operation *_op)
_debug("- copy {%lu}", monitor->back_page->index);
- error = -EIO;
+ recheck:
if (PageUptodate(monitor->back_page)) {
copy_highpage(monitor->netfs_page, monitor->back_page);
pagevec_add(&pagevec, monitor->netfs_page);
fscache_mark_pages_cached(monitor->op, &pagevec);
error = 0;
- }
-
- if (error)
+ } else if (!PageError(monitor->back_page)) {
+ /* the page has probably been truncated */
+ error = cachefiles_read_reissue(object, monitor);
+ if (error == -EINPROGRESS)
+ goto next;
+ goto recheck;
+ } else {
cachefiles_io_error_obj(
object,
"Readpage failed on backing file %lx",
(unsigned long) monitor->back_page->flags);
+ error = -EIO;
+ }
page_cache_release(monitor->back_page);
@@ -114,6 +200,7 @@ static void cachefiles_read_copier(struct fscache_operation *_op)
fscache_put_retrieval(op);
kfree(monitor);
+ next:
/* let the thread pool have some air occasionally */
max--;
if (max < 0 || need_resched()) {
--
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