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![Linus Torvalds](/assets/img/avatar_default.png)
This reverts commit b43d17f319
.
Dave Jones reports that it causes lockups on his laptop, and his debug
output showed a lot of processes hung waiting for page_writeback (or
more commonly - processes hung waiting for a lock that was held during
that writeback wait).
The page_writeback hint made Ted suggest that Dave look at this commit,
and Dave verified that reverting it makes his problems go away.
Ted says:
"That commit fixes a race which is seen when you write into fallocated
(and hence uninitialized) disk blocks under *very* heavy memory
pressure. Furthermore, although theoretically it could trigger under
normal direct I/O writes, it only seems to trigger if you are issuing
a huge number of AIO writes, such that a just-written page can get
evicted from memory, and then read back into memory, before the
workqueue has a chance to update the extent tree.
This race has been around for a little over a year, and no one noticed
until two months ago; it only happens under fairly exotic conditions,
and in fact even after trying very hard to create a simple repro under
lab conditions, we could only reproduce the problem and confirm the
fix on production servers running MySQL on very fast PCIe-attached
flash devices.
Given that Dave was able to hit this problem pretty quickly, if we
confirm that this commit is at fault, the only reasonable thing to do
is to revert it IMO."
Reported-and-tested-by: Dave Jones <davej@redhat.com>
Acked-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
433 lines
11 KiB
C
433 lines
11 KiB
C
/*
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* linux/fs/ext4/page-io.c
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*
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* This contains the new page_io functions for ext4
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*
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* Written by Theodore Ts'o, 2010.
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*/
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#include <linux/fs.h>
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#include <linux/time.h>
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#include <linux/jbd2.h>
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#include <linux/highuid.h>
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#include <linux/pagemap.h>
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#include <linux/quotaops.h>
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#include <linux/string.h>
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#include <linux/buffer_head.h>
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#include <linux/writeback.h>
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#include <linux/pagevec.h>
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#include <linux/mpage.h>
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#include <linux/namei.h>
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#include <linux/uio.h>
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#include <linux/bio.h>
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#include <linux/workqueue.h>
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#include <linux/kernel.h>
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#include <linux/slab.h>
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#include "ext4_jbd2.h"
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#include "xattr.h"
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#include "acl.h"
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#include "ext4_extents.h"
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static struct kmem_cache *io_page_cachep, *io_end_cachep;
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int __init ext4_init_pageio(void)
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{
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io_page_cachep = KMEM_CACHE(ext4_io_page, SLAB_RECLAIM_ACCOUNT);
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if (io_page_cachep == NULL)
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return -ENOMEM;
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io_end_cachep = KMEM_CACHE(ext4_io_end, SLAB_RECLAIM_ACCOUNT);
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if (io_end_cachep == NULL) {
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kmem_cache_destroy(io_page_cachep);
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return -ENOMEM;
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}
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return 0;
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}
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void ext4_exit_pageio(void)
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{
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kmem_cache_destroy(io_end_cachep);
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kmem_cache_destroy(io_page_cachep);
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}
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void ext4_ioend_wait(struct inode *inode)
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{
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wait_queue_head_t *wq = ext4_ioend_wq(inode);
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wait_event(*wq, (atomic_read(&EXT4_I(inode)->i_ioend_count) == 0));
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}
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static void put_io_page(struct ext4_io_page *io_page)
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{
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if (atomic_dec_and_test(&io_page->p_count)) {
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end_page_writeback(io_page->p_page);
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put_page(io_page->p_page);
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kmem_cache_free(io_page_cachep, io_page);
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}
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}
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void ext4_free_io_end(ext4_io_end_t *io)
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{
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int i;
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BUG_ON(!io);
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if (io->page)
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put_page(io->page);
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for (i = 0; i < io->num_io_pages; i++)
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put_io_page(io->pages[i]);
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io->num_io_pages = 0;
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if (atomic_dec_and_test(&EXT4_I(io->inode)->i_ioend_count))
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wake_up_all(ext4_ioend_wq(io->inode));
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kmem_cache_free(io_end_cachep, io);
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}
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/*
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* check a range of space and convert unwritten extents to written.
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*
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* Called with inode->i_mutex; we depend on this when we manipulate
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* io->flag, since we could otherwise race with ext4_flush_completed_IO()
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*/
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int ext4_end_io_nolock(ext4_io_end_t *io)
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{
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struct inode *inode = io->inode;
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loff_t offset = io->offset;
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ssize_t size = io->size;
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int ret = 0;
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ext4_debug("ext4_end_io_nolock: io 0x%p from inode %lu,list->next 0x%p,"
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"list->prev 0x%p\n",
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io, inode->i_ino, io->list.next, io->list.prev);
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ret = ext4_convert_unwritten_extents(inode, offset, size);
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if (ret < 0) {
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ext4_msg(inode->i_sb, KERN_EMERG,
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"failed to convert unwritten extents to written "
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"extents -- potential data loss! "
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"(inode %lu, offset %llu, size %zd, error %d)",
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inode->i_ino, offset, size, ret);
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}
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if (io->iocb)
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aio_complete(io->iocb, io->result, 0);
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if (io->flag & EXT4_IO_END_DIRECT)
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inode_dio_done(inode);
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/* Wake up anyone waiting on unwritten extent conversion */
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if (atomic_dec_and_test(&EXT4_I(inode)->i_aiodio_unwritten))
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wake_up_all(ext4_ioend_wq(io->inode));
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return ret;
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}
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/*
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* work on completed aio dio IO, to convert unwritten extents to extents
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*/
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static void ext4_end_io_work(struct work_struct *work)
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{
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ext4_io_end_t *io = container_of(work, ext4_io_end_t, work);
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struct inode *inode = io->inode;
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struct ext4_inode_info *ei = EXT4_I(inode);
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unsigned long flags;
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spin_lock_irqsave(&ei->i_completed_io_lock, flags);
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if (io->flag & EXT4_IO_END_IN_FSYNC)
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goto requeue;
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if (list_empty(&io->list)) {
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spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
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goto free;
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}
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if (!mutex_trylock(&inode->i_mutex)) {
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bool was_queued;
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requeue:
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was_queued = !!(io->flag & EXT4_IO_END_QUEUED);
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io->flag |= EXT4_IO_END_QUEUED;
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spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
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/*
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* Requeue the work instead of waiting so that the work
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* items queued after this can be processed.
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*/
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queue_work(EXT4_SB(inode->i_sb)->dio_unwritten_wq, &io->work);
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/*
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* To prevent the ext4-dio-unwritten thread from keeping
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* requeueing end_io requests and occupying cpu for too long,
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* yield the cpu if it sees an end_io request that has already
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* been requeued.
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*/
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if (was_queued)
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yield();
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return;
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}
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list_del_init(&io->list);
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spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
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(void) ext4_end_io_nolock(io);
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mutex_unlock(&inode->i_mutex);
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free:
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ext4_free_io_end(io);
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}
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ext4_io_end_t *ext4_init_io_end(struct inode *inode, gfp_t flags)
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{
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ext4_io_end_t *io = kmem_cache_zalloc(io_end_cachep, flags);
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if (io) {
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atomic_inc(&EXT4_I(inode)->i_ioend_count);
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io->inode = inode;
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INIT_WORK(&io->work, ext4_end_io_work);
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INIT_LIST_HEAD(&io->list);
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}
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return io;
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}
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/*
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* Print an buffer I/O error compatible with the fs/buffer.c. This
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* provides compatibility with dmesg scrapers that look for a specific
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* buffer I/O error message. We really need a unified error reporting
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* structure to userspace ala Digital Unix's uerf system, but it's
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* probably not going to happen in my lifetime, due to LKML politics...
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*/
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static void buffer_io_error(struct buffer_head *bh)
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{
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char b[BDEVNAME_SIZE];
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printk(KERN_ERR "Buffer I/O error on device %s, logical block %llu\n",
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bdevname(bh->b_bdev, b),
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(unsigned long long)bh->b_blocknr);
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}
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static void ext4_end_bio(struct bio *bio, int error)
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{
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ext4_io_end_t *io_end = bio->bi_private;
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struct workqueue_struct *wq;
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struct inode *inode;
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unsigned long flags;
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int i;
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sector_t bi_sector = bio->bi_sector;
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BUG_ON(!io_end);
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bio->bi_private = NULL;
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bio->bi_end_io = NULL;
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if (test_bit(BIO_UPTODATE, &bio->bi_flags))
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error = 0;
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bio_put(bio);
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for (i = 0; i < io_end->num_io_pages; i++) {
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struct page *page = io_end->pages[i]->p_page;
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struct buffer_head *bh, *head;
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loff_t offset;
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loff_t io_end_offset;
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if (error) {
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SetPageError(page);
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set_bit(AS_EIO, &page->mapping->flags);
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head = page_buffers(page);
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BUG_ON(!head);
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io_end_offset = io_end->offset + io_end->size;
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offset = (sector_t) page->index << PAGE_CACHE_SHIFT;
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bh = head;
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do {
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if ((offset >= io_end->offset) &&
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(offset+bh->b_size <= io_end_offset))
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buffer_io_error(bh);
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offset += bh->b_size;
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bh = bh->b_this_page;
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} while (bh != head);
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}
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put_io_page(io_end->pages[i]);
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}
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io_end->num_io_pages = 0;
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inode = io_end->inode;
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if (error) {
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io_end->flag |= EXT4_IO_END_ERROR;
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ext4_warning(inode->i_sb, "I/O error writing to inode %lu "
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"(offset %llu size %ld starting block %llu)",
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inode->i_ino,
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(unsigned long long) io_end->offset,
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(long) io_end->size,
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(unsigned long long)
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bi_sector >> (inode->i_blkbits - 9));
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}
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if (!(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
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ext4_free_io_end(io_end);
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return;
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}
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/* Add the io_end to per-inode completed io list*/
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spin_lock_irqsave(&EXT4_I(inode)->i_completed_io_lock, flags);
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list_add_tail(&io_end->list, &EXT4_I(inode)->i_completed_io_list);
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spin_unlock_irqrestore(&EXT4_I(inode)->i_completed_io_lock, flags);
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wq = EXT4_SB(inode->i_sb)->dio_unwritten_wq;
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/* queue the work to convert unwritten extents to written */
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queue_work(wq, &io_end->work);
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}
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void ext4_io_submit(struct ext4_io_submit *io)
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{
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struct bio *bio = io->io_bio;
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if (bio) {
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bio_get(io->io_bio);
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submit_bio(io->io_op, io->io_bio);
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BUG_ON(bio_flagged(io->io_bio, BIO_EOPNOTSUPP));
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bio_put(io->io_bio);
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}
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io->io_bio = NULL;
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io->io_op = 0;
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io->io_end = NULL;
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}
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static int io_submit_init(struct ext4_io_submit *io,
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struct inode *inode,
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struct writeback_control *wbc,
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struct buffer_head *bh)
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{
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ext4_io_end_t *io_end;
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struct page *page = bh->b_page;
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int nvecs = bio_get_nr_vecs(bh->b_bdev);
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struct bio *bio;
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io_end = ext4_init_io_end(inode, GFP_NOFS);
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if (!io_end)
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return -ENOMEM;
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bio = bio_alloc(GFP_NOIO, min(nvecs, BIO_MAX_PAGES));
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bio->bi_sector = bh->b_blocknr * (bh->b_size >> 9);
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bio->bi_bdev = bh->b_bdev;
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bio->bi_private = io->io_end = io_end;
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bio->bi_end_io = ext4_end_bio;
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io_end->offset = (page->index << PAGE_CACHE_SHIFT) + bh_offset(bh);
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io->io_bio = bio;
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io->io_op = (wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : WRITE);
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io->io_next_block = bh->b_blocknr;
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return 0;
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}
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static int io_submit_add_bh(struct ext4_io_submit *io,
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struct ext4_io_page *io_page,
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struct inode *inode,
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struct writeback_control *wbc,
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struct buffer_head *bh)
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{
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ext4_io_end_t *io_end;
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int ret;
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if (buffer_new(bh)) {
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clear_buffer_new(bh);
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unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
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}
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if (!buffer_mapped(bh) || buffer_delay(bh)) {
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if (!buffer_mapped(bh))
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clear_buffer_dirty(bh);
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if (io->io_bio)
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ext4_io_submit(io);
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return 0;
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}
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if (io->io_bio && bh->b_blocknr != io->io_next_block) {
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submit_and_retry:
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ext4_io_submit(io);
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}
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if (io->io_bio == NULL) {
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ret = io_submit_init(io, inode, wbc, bh);
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if (ret)
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return ret;
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}
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io_end = io->io_end;
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if ((io_end->num_io_pages >= MAX_IO_PAGES) &&
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(io_end->pages[io_end->num_io_pages-1] != io_page))
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goto submit_and_retry;
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if (buffer_uninit(bh))
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ext4_set_io_unwritten_flag(inode, io_end);
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io->io_end->size += bh->b_size;
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io->io_next_block++;
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ret = bio_add_page(io->io_bio, bh->b_page, bh->b_size, bh_offset(bh));
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if (ret != bh->b_size)
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goto submit_and_retry;
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if ((io_end->num_io_pages == 0) ||
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(io_end->pages[io_end->num_io_pages-1] != io_page)) {
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io_end->pages[io_end->num_io_pages++] = io_page;
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atomic_inc(&io_page->p_count);
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}
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return 0;
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}
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int ext4_bio_write_page(struct ext4_io_submit *io,
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struct page *page,
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int len,
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struct writeback_control *wbc)
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{
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struct inode *inode = page->mapping->host;
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unsigned block_start, block_end, blocksize;
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struct ext4_io_page *io_page;
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struct buffer_head *bh, *head;
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int ret = 0;
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blocksize = 1 << inode->i_blkbits;
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BUG_ON(!PageLocked(page));
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BUG_ON(PageWriteback(page));
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io_page = kmem_cache_alloc(io_page_cachep, GFP_NOFS);
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if (!io_page) {
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set_page_dirty(page);
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unlock_page(page);
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return -ENOMEM;
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}
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io_page->p_page = page;
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atomic_set(&io_page->p_count, 1);
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get_page(page);
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set_page_writeback(page);
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ClearPageError(page);
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for (bh = head = page_buffers(page), block_start = 0;
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bh != head || !block_start;
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block_start = block_end, bh = bh->b_this_page) {
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block_end = block_start + blocksize;
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if (block_start >= len) {
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/*
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* Comments copied from block_write_full_page_endio:
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*
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* The page straddles i_size. It must be zeroed out on
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* each and every writepage invocation because it may
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* be mmapped. "A file is mapped in multiples of the
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* page size. For a file that is not a multiple of
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* the page size, the remaining memory is zeroed when
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* mapped, and writes to that region are not written
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* out to the file."
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*/
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zero_user_segment(page, block_start, block_end);
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clear_buffer_dirty(bh);
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set_buffer_uptodate(bh);
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continue;
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}
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clear_buffer_dirty(bh);
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ret = io_submit_add_bh(io, io_page, inode, wbc, bh);
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if (ret) {
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/*
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* We only get here on ENOMEM. Not much else
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* we can do but mark the page as dirty, and
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* better luck next time.
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*/
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set_page_dirty(page);
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break;
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}
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}
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unlock_page(page);
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/*
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* If the page was truncated before we could do the writeback,
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* or we had a memory allocation error while trying to write
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* the first buffer head, we won't have submitted any pages for
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* I/O. In that case we need to make sure we've cleared the
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* PageWriteback bit from the page to prevent the system from
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* wedging later on.
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*/
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put_io_page(io_page);
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return ret;
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}
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