[PATCH 1/3] ext4: nonda_switch prevent deadlock
STALE5146d
From: Dmitry Monakhov <hidden>
Date: 2012-08-28 16:22:01
Subsystem:
ext4 file system, filesystems (vfs and infrastructure), the rest · Maintainers:
"Theodore Ts'o", Alexander Viro, Christian Brauner, Linus Torvalds
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