[f2fs-dev] [PATCH] f2fs: fix lock dependency in between dio_rwsem & i_mmap_sem

[Chao Yu]

From: Chao Yu <yuch...@huawei.com>

test/generic/208 reports a potential deadlock as below:

Chain exists of:
  &mm->mmap_sem --> &fi->i_mmap_sem --> &fi->dio_rwsem[WRITE]

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&fi->dio_rwsem[WRITE]);
                               lock(&fi->i_mmap_sem);
                               lock(&fi->dio_rwsem[WRITE]);
  lock(&mm->mmap_sem);

This patch changes the lock dependency as below in fallocate() to
fix this issue:
- dio_rwsem
 - i_mmap_sem

Fixes: bb06664a534b ("f2fs: avoid race in between GC and block exchange")
Signed-off-by: Chao Yu <yuch...@huawei.com>
---
 fs/f2fs/file.c | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index a292a1a3a692..d08e003e6d6b 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1185,14 +1185,14 @@ static int f2fs_collapse_range(struct inode *inode, 
loff_t offset, loff_t len)
        pg_start = offset >> PAGE_SHIFT;
        pg_end = (offset + len) >> PAGE_SHIFT;
 
+       /* avoid gc operation during block exchange */
+       down_write(&F2FS_I(inode)->dio_rwsem[WRITE]);
+
        down_write(&F2FS_I(inode)->i_mmap_sem);
        /* write out all dirty pages from offset */
        ret = filemap_write_and_wait_range(inode->i_mapping, offset, LLONG_MAX);
        if (ret)
-               goto out;
-
-       /* avoid gc operation during block exchange */
-       down_write(&F2FS_I(inode)->dio_rwsem[WRITE]);
+               goto out_unlock;
 
        truncate_pagecache(inode, offset);
 
@@ -1211,9 +1211,8 @@ static int f2fs_collapse_range(struct inode *inode, 
loff_t offset, loff_t len)
        if (!ret)
                f2fs_i_size_write(inode, new_size);
 out_unlock:
-       up_write(&F2FS_I(inode)->dio_rwsem[WRITE]);
-out:
        up_write(&F2FS_I(inode)->i_mmap_sem);
+       up_write(&F2FS_I(inode)->dio_rwsem[WRITE]);
        return ret;
 }
 
@@ -1384,6 +1383,9 @@ static int f2fs_insert_range(struct inode *inode, loff_t 
offset, loff_t len)
 
        f2fs_balance_fs(sbi, true);
 
+       /* avoid gc operation during block exchange */
+       down_write(&F2FS_I(inode)->dio_rwsem[WRITE]);
+
        down_write(&F2FS_I(inode)->i_mmap_sem);
        ret = truncate_blocks(inode, i_size_read(inode), true);
        if (ret)
@@ -1394,9 +1396,6 @@ static int f2fs_insert_range(struct inode *inode, loff_t 
offset, loff_t len)
        if (ret)
                goto out;
 
-       /* avoid gc operation during block exchange */
-       down_write(&F2FS_I(inode)->dio_rwsem[WRITE]);
-
        truncate_pagecache(inode, offset);
 
        pg_start = offset >> PAGE_SHIFT;
@@ -1424,10 +1423,9 @@ static int f2fs_insert_range(struct inode *inode, loff_t 
offset, loff_t len)
 
        if (!ret)
                f2fs_i_size_write(inode, new_size);
-
-       up_write(&F2FS_I(inode)->dio_rwsem[WRITE]);
 out:
        up_write(&F2FS_I(inode)->i_mmap_sem);
+       up_write(&F2FS_I(inode)->dio_rwsem[WRITE]);
        return ret;
 }
 
-- 
2.14.1.145.gb3622a4ee


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