Currently ext4_da_write_begin may deadlock if called with opened journal
transaction. Real life example:
->move_extent_per_page()
->ext4_journal_start()-> hold journal transaction
->write_begin()
->ext4_da_write_begin()
->ext4_nonda_switch()
->writeback_inodes_sb_if_idle() --> will wait for journal_stop()
This bug may be easily fixed by code reordering,
But in some cases it should be possible to call write_begin()
while holding journal's transaction, in this case caller may avoid
recoursion by passing AOP_FLAG_NOFS flag.
---
fs/ext4/inode.c | 28 +++++++++++++++++-----------
1 files changed, 17 insertions(+), 11 deletions(-)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 6324f74..d12d30e 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -889,6 +889,11 @@ static int ext4_write_begin(struct file *file, struct address_space *mapping,
struct page *page;
pgoff_t index;
unsigned from, to;
+ int nofs = flags & AOP_FLAG_NOFS;
+
+ /* We cannot recurse into the filesystem if the transaction is already
+ * started */
+ BUG_ON(!nofs && journal_current_handle());
trace_ext4_write_begin(inode, pos, len, flags);
/*
@@ -906,9 +911,6 @@ retry:
ret = PTR_ERR(handle);
goto out;
}
-
- /* We cannot recurse into the filesystem as the transaction is already
- * started */
flags |= AOP_FLAG_NOFS;
page = grab_cache_page_write_begin(mapping, index, flags);
@@ -957,7 +959,8 @@ retry:
}
}
- if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
+ if (!nofs && ret == -ENOSPC &&
+ ext4_should_retry_alloc(inode->i_sb, &retries))
goto retry;
out:
return ret;
@@ -2447,7 +2450,7 @@ out_writepages:
}
#define FALL_BACK_TO_NONDELALLOC 1
-static int ext4_nonda_switch(struct super_block *sb)
+static int ext4_nonda_switch(struct super_block *sb, int writeback_allowed)
{
s64 free_blocks, dirty_blocks;
struct ext4_sb_info *sbi = EXT4_SB(sb);
@@ -2475,7 +2478,7 @@ static int ext4_nonda_switch(struct super_block *sb)
* Even if we don't switch but are nearing capacity,
* start pushing delalloc when 1/2 of free blocks are dirty.
*/
- if (free_blocks < 2 * dirty_blocks)
+ if (writeback_allowed && free_blocks < 2 * dirty_blocks)
writeback_inodes_sb_if_idle(sb, WB_REASON_FS_FREE_SPACE);
return 0;
@@ -2490,10 +2493,14 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
pgoff_t index;
struct inode *inode = mapping->host;
handle_t *handle;
+ int nofs = flags & AOP_FLAG_NOFS;
index = pos >> PAGE_CACHE_SHIFT;
+ /* We cannot recurse into the filesystem if the transaction is already
+ * started */
+ BUG_ON(!nofs && journal_current_handle());
- if (ext4_nonda_switch(inode->i_sb)) {
+ if (ext4_nonda_switch(inode->i_sb, !nofs)) {
*fsdata = (void *)FALL_BACK_TO_NONDELALLOC;
return ext4_write_begin(file, mapping, pos,
len, flags, pagep, fsdata);
@@ -2512,8 +2519,6 @@ retry:
ret = PTR_ERR(handle);
goto out;
}
- /* We cannot recurse into the filesystem as the transaction is already
- * started */
flags |= AOP_FLAG_NOFS;
page = grab_cache_page_write_begin(mapping, index, flags);
@@ -2538,7 +2543,8 @@ retry:
ext4_truncate_failed_write(inode);
}
- if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
+ if (!nofs && ret == -ENOSPC &&
+ ext4_should_retry_alloc(inode->i_sb, &retries))
goto retry;
out:
return ret;
@@ -4791,7 +4797,7 @@ int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
/* Delalloc case is easy... */
if (test_opt(inode->i_sb, DELALLOC) &&
!ext4_should_journal_data(inode) &&
- !ext4_nonda_switch(inode->i_sb)) {
+ !ext4_nonda_switch(inode->i_sb, 1)) {
do {
ret = __block_page_mkwrite(vma, vmf,
ext4_da_get_block_prep);
--
1.7.7.6
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