Re: [f2fs-dev] [PATCH v2] f2fs: fix to keep isolation of atomic write
From: Chao Yu
Date: Tue Jan 12 2021 - 20:31:22 EST
On 2021/1/13 6:32, Jaegeuk Kim wrote:
On 01/12, Chao Yu wrote:
On 2021/1/12 0:32, Jaegeuk Kim wrote:
On 01/06, Jaegeuk Kim wrote:
On 01/06, Jaegeuk Kim wrote:
Hi Chao,
With a quick test, this patch causes down_write failure resulting in blocking
process. I didn't dig in the bug so, please check the code again. :P
nvm. I can see it works now.
Hmm, this gives a huge perf regression when running sqlite. :(
We may need to check the lock coverage. Thoughts?
I added i_mmap_sem lock only, so it can cause atomic_{start,commit,finish}
race with mmap and truncation operations in additionally.
I'd like to know what's your sqlite testcase?
Nothing special. Just generating multiple sqlite transactions to the same db.
I doubt that start/commit flow race with ->release/->flush interface can cause
lower concurrency?
f2fs_ioc_start_atomic_write or ->release or ->flush
f2fs_ioc_commit_atomic_write
- f2fs_drop_inmem_pages
down_write(&F2FS_I(inode)->i_mmap_sem);
down_write(&F2FS_I(inode)->i_mmap_sem);
How about trying this testcase again after removing i_mmap_sem lock in
f2fs_drop_inmem_pages()?
Thanks,
Thanks,
On 12/30, Chao Yu wrote:
ThreadA ThreadB
- f2fs_ioc_start_atomic_write
- write
- f2fs_ioc_commit_atomic_write
- f2fs_commit_inmem_pages
- f2fs_drop_inmem_pages
- f2fs_drop_inmem_pages
- __revoke_inmem_pages
- f2fs_vm_page_mkwrite
- set_page_dirty
- tag ATOMIC_WRITTEN_PAGE and add page
to inmem_pages list
- clear_inode_flag(FI_ATOMIC_FILE)
- f2fs_vm_page_mkwrite
- set_page_dirty
- f2fs_update_dirty_page
- f2fs_trace_pid
- tag inmem page private to pid
- truncate
- f2fs_invalidate_page
- set page->mapping to NULL
then it will cause panic once we
access page->mapping
The root cause is we missed to keep isolation of atomic write in the case
of commit_atomic_write vs mkwrite, let commit_atomic_write helds i_mmap_sem
lock to avoid this issue.
Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
---
v2:
- use i_mmap_sem to avoid mkwrite racing with below flows:
* f2fs_ioc_start_atomic_write
* f2fs_drop_inmem_pages
* f2fs_commit_inmem_pages
fs/f2fs/file.c | 3 +++
fs/f2fs/segment.c | 7 +++++++
2 files changed, 10 insertions(+)
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 4e6d4b9120a8..a48ec650d691 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -2050,6 +2050,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
goto out;
down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
+ down_write(&F2FS_I(inode)->i_mmap_sem);
/*
* Should wait end_io to count F2FS_WB_CP_DATA correctly by
@@ -2060,6 +2061,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
inode->i_ino, get_dirty_pages(inode));
ret = filemap_write_and_wait_range(inode->i_mapping, 0, LLONG_MAX);
if (ret) {
+ up_write(&F2FS_I(inode)->i_mmap_sem);
up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
goto out;
}
@@ -2073,6 +2075,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
/* add inode in inmem_list first and set atomic_file */
set_inode_flag(inode, FI_ATOMIC_FILE);
clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
+ up_write(&F2FS_I(inode)->i_mmap_sem);
up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
f2fs_update_time(F2FS_I_SB(inode), REQ_TIME);
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index d8570b0359f5..dab870d9faf6 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -327,6 +327,8 @@ 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);
+ down_write(&F2FS_I(inode)->i_mmap_sem);
+
while (!list_empty(&fi->inmem_pages)) {
mutex_lock(&fi->inmem_lock);
__revoke_inmem_pages(inode, &fi->inmem_pages,
@@ -344,6 +346,8 @@ void f2fs_drop_inmem_pages(struct inode *inode)
sbi->atomic_files--;
}
spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
+
+ up_write(&F2FS_I(inode)->i_mmap_sem);
}
void f2fs_drop_inmem_page(struct inode *inode, struct page *page)
@@ -467,6 +471,7 @@ int f2fs_commit_inmem_pages(struct inode *inode)
f2fs_balance_fs(sbi, true);
down_write(&fi->i_gc_rwsem[WRITE]);
+ down_write(&F2FS_I(inode)->i_mmap_sem);
f2fs_lock_op(sbi);
set_inode_flag(inode, FI_ATOMIC_COMMIT);
@@ -478,6 +483,8 @@ int f2fs_commit_inmem_pages(struct inode *inode)
clear_inode_flag(inode, FI_ATOMIC_COMMIT);
f2fs_unlock_op(sbi);
+
+ up_write(&F2FS_I(inode)->i_mmap_sem);
up_write(&fi->i_gc_rwsem[WRITE]);
return err;
--
2.29.2
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