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f2fs: Fix a hungtask problem in atomic write

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In the cache writing process, if it is an atomic file, increase the page
count of F2FS_WB_CP_DATA, otherwise increase the page count of
F2FS_WB_DATA.

When you step into the hook branch due to insufficient memory in
f2fs_write_begin, f2fs_drop_inmem_pages_all will be called to traverse
all atomic inodes and clear the FI_ATOMIC_FILE mark of all atomic files.

In f2fs_drop_inmem_pages，first acquire the inmem_lock , revoke all the
inmem_pages, and then clear the FI_ATOMIC_FILE mark. Before this mark is
cleared, other threads may hold inmem_lock to add inmem_pages to the inode
that has just been emptied inmem_pages, and increase the page count of
F2FS_WB_CP_DATA.

When the IO returns, it is found that the FI_ATOMIC_FILE flag is cleared
by f2fs_drop_inmem_pages_all, and f2fs_is_atomic_file returns false,which
causes the page count of F2FS_WB_DATA to be decremented. The page count of
F2FS_WB_CP_DATA cannot be cleared. Finally, hungtask is triggered in
f2fs_wait_on_all_pages because get_pages will never return zero.

process A:				process B:
f2fs_drop_inmem_pages_all
->f2fs_drop_inmem_pages of inode#1
    ->mutex_lock(&fi->inmem_lock)
    ->__revoke_inmem_pages of inode#1	f2fs_ioc_commit_atomic_write
    ->mutex_unlock(&fi->inmem_lock)	->f2fs_commit_inmem_pages of inode#1
					->mutex_lock(&fi->inmem_lock)
					->__f2fs_commit_inmem_pages
					    ->f2fs_do_write_data_page
					        ->f2fs_outplace_write_data
					            ->do_write_page
					                ->f2fs_submit_page_write
					                    ->inc_page_count(sbi, F2FS_WB_CP_DATA )
					->mutex_unlock(&fi->inmem_lock)
    ->spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
    ->clear_inode_flag(inode, FI_ATOMIC_FILE)
    ->spin_unlock(&sbi->inode_lock[ATOMIC_FILE])
					f2fs_write_end_io
					->dec_page_count(sbi, F2FS_WB_DATA );

We can fix the problem by putting the action of clearing the FI_ATOMIC_FILE
mark into the inmem_lock lock. This operation can ensure that no one will
submit the inmem pages before the FI_ATOMIC_FILE mark is cleared, so that
there will be no atomic writes waiting for writeback.

Fixes: 57864ae5ce3a ("f2fs: limit # of inmemory pages")
Signed-off-by: Yi Zhuang <zhuangyi1@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
This commit is contained in:
Yi Zhuang 2021-03-31 17:34:14 +08:00 committed by Jaegeuk Kim
parent 23738e7447
commit be1ee45d51
1 changed files with 17 additions and 13 deletions
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30
fs/f2fs/segment.c
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@ -324,23 +324,27 @@ void f2fs_drop_inmem_pages(struct inode *inode)
struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
struct f2fs_inode_info *fi = F2FS_I(inode);
while (!list_empty(&fi->inmem_pages)) {
do {
mutex_lock(&fi->inmem_lock);
if (list_empty(&fi->inmem_pages)) {
fi->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
if (!list_empty(&fi->inmem_ilist))
list_del_init(&fi->inmem_ilist);
if (f2fs_is_atomic_file(inode)) {
clear_inode_flag(inode, FI_ATOMIC_FILE);
sbi->atomic_files--;
}
spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
mutex_unlock(&fi->inmem_lock);
break;
}
__revoke_inmem_pages(inode, &fi->inmem_pages,
true, false, true);
mutex_unlock(&fi->inmem_lock);
}
fi->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
if (!list_empty(&fi->inmem_ilist))
list_del_init(&fi->inmem_ilist);
if (f2fs_is_atomic_file(inode)) {
clear_inode_flag(inode, FI_ATOMIC_FILE);
sbi->atomic_files--;
}
spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
} while (1);
}
void f2fs_drop_inmem_page(struct inode *inode, struct page *page)