Re: [f2fs-dev] [PATCH 2/2] f2fs: avoid infinite GC loop due to stale atomic files

From: Jaegeuk Kim
Date: Mon Sep 09 2019 - 10:34:24 EST

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In reply to: Chao Yu: "Re: [f2fs-dev] [PATCH 2/2] f2fs: avoid infinite GC loop due to stale atomic files"
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On 09/09, Chao Yu wrote:
> On 2019/9/9 16:38, Jaegeuk Kim wrote:
> > On 09/09, Chao Yu wrote:
> >> On 2019/9/9 16:21, Jaegeuk Kim wrote:
> >>> On 09/09, Chao Yu wrote:
> >>>> On 2019/9/9 16:01, Jaegeuk Kim wrote:
> >>>>> On 09/09, Chao Yu wrote:
> >>>>>> On 2019/9/9 15:30, Jaegeuk Kim wrote:
> >>>>>>> On 09/09, Chao Yu wrote:
> >>>>>>>> On 2019/9/9 9:25, Jaegeuk Kim wrote:
> >>>>>>>>> If committing atomic pages is failed when doing f2fs_do_sync_file(), we can
> >>>>>>>>> get commited pages but atomic_file being still set like:
> >>>>>>>>>
> >>>>>>>>> - inmem: 0, atomic IO: 4 (Max. 10), volatile IO: 0 (Max. 0)
> >>>>>>>>>
> >>>>>>>>> If GC selects this block, we can get an infinite loop like this:
> >>>>>>>>>
> >>>>>>>>> f2fs_submit_page_bio: dev = (253,7), ino = 2, page_index = 0x2359a8, oldaddr = 0x2359a8, newaddr = 0x2359a8, rw = READ(), type = COLD_DATA
> >>>>>>>>> f2fs_submit_read_bio: dev = (253,7)/(253,7), rw = READ(), DATA, sector = 18533696, size = 4096
> >>>>>>>>> f2fs_get_victim: dev = (253,7), type = No TYPE, policy = (Foreground GC, LFS-mode, Greedy), victim = 4355, cost = 1, ofs_unit = 1, pre_victim_secno = 4355, prefree = 0, free = 234
> >>>>>>>>> f2fs_iget: dev = (253,7), ino = 6247, pino = 5845, i_mode = 0x81b0, i_size = 319488, i_nlink = 1, i_blocks = 624, i_advise = 0x2c
> >>>>>>>>> f2fs_submit_page_bio: dev = (253,7), ino = 2, page_index = 0x2359a8, oldaddr = 0x2359a8, newaddr = 0x2359a8, rw = READ(), type = COLD_DATA
> >>>>>>>>> f2fs_submit_read_bio: dev = (253,7)/(253,7), rw = READ(), DATA, sector = 18533696, size = 4096
> >>>>>>>>> f2fs_get_victim: dev = (253,7), type = No TYPE, policy = (Foreground GC, LFS-mode, Greedy), victim = 4355, cost = 1, ofs_unit = 1, pre_victim_secno = 4355, prefree = 0, free = 234
> >>>>>>>>> f2fs_iget: dev = (253,7), ino = 6247, pino = 5845, i_mode = 0x81b0, i_size = 319488, i_nlink = 1, i_blocks = 624, i_advise = 0x2c
> >>>>>>>>>
> >>>>>>>>> In that moment, we can observe:
> >>>>>>>>>
> >>>>>>>>> [Before]
> >>>>>>>>> Try to move 5084219 blocks (BG: 384508)
> >>>>>>>>> - data blocks : 4962373 (274483)
> >>>>>>>>> - node blocks : 121846 (110025)
> >>>>>>>>> Skipped : atomic write 4534686 (10)
> >>>>>>>>>
> >>>>>>>>> [After]
> >>>>>>>>> Try to move 5088973 blocks (BG: 384508)
> >>>>>>>>> - data blocks : 4967127 (274483)
> >>>>>>>>> - node blocks : 121846 (110025)
> >>>>>>>>> Skipped : atomic write 4539440 (10)
> >>>>>>>>>
> >>>>>>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> >>>>>>>>> ---
> >>>>>>>>> fs/f2fs/file.c | 10 +++++-----
> >>>>>>>>> 1 file changed, 5 insertions(+), 5 deletions(-)
> >>>>>>>>>
> >>>>>>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> >>>>>>>>> index 7ae2f3bd8c2f..68b6da734e5f 100644
> >>>>>>>>> --- a/fs/f2fs/file.c
> >>>>>>>>> +++ b/fs/f2fs/file.c
> >>>>>>>>> @@ -1997,11 +1997,11 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
> >>>>>>>>> goto err_out;
> >>>>>>>>>
> >>>>>>>>> ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 0, true);
> >>>>>>>>> - if (!ret) {
> >>>>>>>>> - clear_inode_flag(inode, FI_ATOMIC_FILE);
> >>>>>>>>> - F2FS_I(inode)->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
> >>>>>>>>> - stat_dec_atomic_write(inode);
> >>>>>>>>> - }
> >>>>>>>>> +
> >>>>>>>>> + /* doesn't need to check error */
> >>>>>>>>> + clear_inode_flag(inode, FI_ATOMIC_FILE);
> >>>>>>>>> + F2FS_I(inode)->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
> >>>>>>>>> + stat_dec_atomic_write(inode);
> >>>>>>>>
> >>>>>>>> If there are still valid atomic write pages linked in .inmem_pages, it may cause
> >>>>>>>> memory leak when we just clear FI_ATOMIC_FILE flag.
> >>>>>>>
> >>>>>>> f2fs_commit_inmem_pages() should have flushed them.
> >>>>>>
> >>>>>> Oh, we failed to flush its nodes.
> >>>>>>
> >>>>>> However we won't clear such info if we failed to flush inmen pages, it looks
> >>>>>> inconsistent.
> >>>>>>
> >>>>>> Any interface needed to drop inmem pages or clear ATOMIC_FILE flag in that two
> >>>>>> error path? I'm not very clear how sqlite handle such error.
> >>>>>
> >>>>> f2fs_drop_inmem_pages() did that, but not in this case.
> >>>>
> >>>> What I mean is, for any error returned from atomic_commit() interface, should
> >>>> userspace application handle it with consistent way, like trigger
> >>>> f2fs_drop_inmem_pages(), so we don't need to handle it inside atomic_commit().
> >>>
> >>> f2fs_ioc_abort_volatile_write() will be triggered.
> >>
> >> If userspace can do this, we can get rid of this patch, or am I missing sth?
> >
> > We don't know when that will come. And, other threads are waiting for GC here.
>
> Yes, however, even atomic_write won't be called sometimes... that's why we add
> handling logic in f2fs_gc().

We need to clean this up like:

If committing atomic pages is failed when doing f2fs_do_sync_file(), we can
get commited pages but atomic_file being still set like:

- inmem: 0, atomic IO: 4 (Max. 10), volatile IO: 0 (Max. 0)

If GC selects this block, we can get an infinite loop like this:

f2fs_submit_page_bio: dev = (253,7), ino = 2, page_index = 0x2359a8, oldaddr = 0x2359a8, newaddr = 0x2359a8, rw = READ(), type = COLD_DATA
f2fs_submit_read_bio: dev = (253,7)/(253,7), rw = READ(), DATA, sector = 18533696, size = 4096
f2fs_get_victim: dev = (253,7), type = No TYPE, policy = (Foreground GC, LFS-mode, Greedy), victim = 4355, cost = 1, ofs_unit = 1, pre_victim_secno = 4355, prefree = 0, free = 234
f2fs_iget: dev = (253,7), ino = 6247, pino = 5845, i_mode = 0x81b0, i_size = 319488, i_nlink = 1, i_blocks = 624, i_advise = 0x2c
f2fs_submit_page_bio: dev = (253,7), ino = 2, page_index = 0x2359a8, oldaddr = 0x2359a8, newaddr = 0x2359a8, rw = READ(), type = COLD_DATA
f2fs_submit_read_bio: dev = (253,7)/(253,7), rw = READ(), DATA, sector = 18533696, size = 4096
f2fs_get_victim: dev = (253,7), type = No TYPE, policy = (Foreground GC, LFS-mode, Greedy), victim = 4355, cost = 1, ofs_unit = 1, pre_victim_secno = 4355, prefree = 0, free = 234
f2fs_iget: dev = (253,7), ino = 6247, pino = 5845, i_mode = 0x81b0, i_size = 319488, i_nlink = 1, i_blocks = 624, i_advise = 0x2c

In that moment, we can observe:

[Before]
Try to move 5084219 blocks (BG: 384508)
- data blocks : 4962373 (274483)
- node blocks : 121846 (110025)
Skipped : atomic write 4534686 (10)

[After]
Try to move 5088973 blocks (BG: 384508)
- data blocks : 4967127 (274483)
- node blocks : 121846 (110025)
Skipped : atomic write 4539440 (10)

So, refactor atomic_write flow like this:
1. start_atomic_write
- add inmem_list and set atomic_file

2. write()
- register it in inmem_pages

3. commit_atomic_write
- if no error, f2fs_drop_inmem_pages()
- f2fs_commit_inmme_pages() failed
: __revoked_inmem_pages() was done
- f2fs_do_sync_file failed
: abort_atomic_write later

4. abort_atomic_write
- f2fs_drop_inmem_pages

5. f2fs_drop_inmem_pages
- clear atomic_file
- remove inmem_list

Based on this change, when GC fails to move block in atomic_file,
f2fs_drop_inmem_pages_all() can call f2fs_drop_inmem_pages().

Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
---
fs/f2fs/file.c | 17 +++++++++++------
fs/f2fs/segment.c | 24 +++++-------------------
2 files changed, 16 insertions(+), 25 deletions(-)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 10927a0b8df3..1f499ac13d9a 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1830,6 +1830,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
{
struct inode *inode = file_inode(filp);
int ret;
+ struct f2fs_inode_info *fi = F2FS_I(inode);

if (!inode_owner_or_capable(inode))
return -EACCES;
@@ -1871,10 +1872,17 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
goto out;
}

- set_inode_flag(inode, FI_ATOMIC_FILE);
clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);

+ spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
+ if (list_empty(&fi->inmem_ilist))
+ list_add_tail(&fi->inmem_ilist, &sbi->inode_list[ATOMIC_FILE]);
+ spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
+
+ /* add inode in inmem_list first and set atomic_file */
+ set_inode_flag(inode, FI_ATOMIC_FILE);
+
f2fs_update_time(F2FS_I_SB(inode), REQ_TIME);
F2FS_I(inode)->inmem_task = current;
stat_inc_atomic_write(inode);
@@ -1912,11 +1920,8 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
goto err_out;

ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 0, true);
- if (!ret) {
- clear_inode_flag(inode, FI_ATOMIC_FILE);
- F2FS_I(inode)->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
- stat_dec_atomic_write(inode);
- }
+ if (!ret)
+ f2fs_drop_inmem_pages(inode);
} else {
ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 1, false);
}
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 18584d4c078a..a36bc8bf04c3 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -186,7 +186,6 @@ bool f2fs_need_SSR(struct f2fs_sb_info *sbi)
void f2fs_register_inmem_page(struct inode *inode, struct page *page)
{
struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
- struct f2fs_inode_info *fi = F2FS_I(inode);
struct inmem_pages *new;

f2fs_trace_pid(page);
@@ -200,15 +199,9 @@ void f2fs_register_inmem_page(struct inode *inode, struct page *page)
INIT_LIST_HEAD(&new->list);

/* increase reference count with clean state */
- mutex_lock(&fi->inmem_lock);
get_page(page);
list_add_tail(&new->list, &fi->inmem_pages);
- spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
- if (list_empty(&fi->inmem_ilist))
- list_add_tail(&fi->inmem_ilist, &sbi->inode_list[ATOMIC_FILE]);
- spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
inc_page_count(F2FS_I_SB(inode), F2FS_INMEM_PAGES);
- mutex_unlock(&fi->inmem_lock);

trace_f2fs_register_inmem_page(page, INMEM);
}
@@ -330,19 +323,17 @@ void f2fs_drop_inmem_pages(struct inode *inode)
mutex_lock(&fi->inmem_lock);
__revoke_inmem_pages(inode, &fi->inmem_pages,
true, false, true);
-
- if (list_empty(&fi->inmem_pages)) {
- spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
- if (!list_empty(&fi->inmem_ilist))
- list_del_init(&fi->inmem_ilist);
- spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
- }
mutex_unlock(&fi->inmem_lock);
}

clear_inode_flag(inode, FI_ATOMIC_FILE);
fi->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
stat_dec_atomic_write(inode);
+
+ spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
+ if (!list_empty(&fi->inmem_ilist))
+ list_del_init(&fi->inmem_ilist);
+ spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
}

void f2fs_drop_inmem_page(struct inode *inode, struct page *page)
@@ -471,11 +462,6 @@ int f2fs_commit_inmem_pages(struct inode *inode)

mutex_lock(&fi->inmem_lock);
err = __f2fs_commit_inmem_pages(inode);
-
- spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
- if (!list_empty(&fi->inmem_ilist))
- list_del_init(&fi->inmem_ilist);
- spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
mutex_unlock(&fi->inmem_lock);

clear_inode_flag(inode, FI_ATOMIC_COMMIT);
--
2.19.0.605.g01d371f741-goog

Next message: Masahiro Yamada: "Re: [PATCH 1/2] export.h: remove defined(__KERNEL__)"
Previous message: Julio Faracco: "[PATCH v2] staging: greybus: loopback_test: Adding missing brackets into if..else block"
In reply to: Chao Yu: "Re: [f2fs-dev] [PATCH 2/2] f2fs: avoid infinite GC loop due to stale atomic files"
Next in thread: Chao Yu: "Re: [f2fs-dev] [PATCH 2/2] f2fs: avoid infinite GC loop due to stale atomic files"
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