[PATCH 0/3] jbd2: some fixes and cleanup about "jbd2: fix several checkpoint inconsistent issues"

[PATCH 0/3] jbd2: some fixes and cleanup about "jbd2: fix several checkpoint inconsistent issues"

[Zhang Yi]

From: Zhang Yi <yi.zhang@huawei.com>

These patch set includes 2 fixes and 1 cleanup about "jbd2: fix several
checkpoint inconsistent issues" patch set[1] recently applied in dev
branch. The first patch fix a performance regression introduced while
merging journal_shrink_one_cp_list(). The second one add a missing
check before dropping checkpoint buffer that could lead to filesystem
inconsistent. The last patch which is from Yang Li, remove the unused
__cp_buffer_busy() helper. Please see the corresponding patch for
details.

[1] https://lore.kernel.org/linux-ext4/168918657577.3681557.17979362698032386800.b4-ty@mit.edu/T/#t

Thanks,
Yi.

Yang Li (1):
  jbd2: remove unused function '__cp_buffer_busy'

Zhang Yi (1):
  jbd2: fix checkpoint cleanup performance regression

Zhihao Cheng (1):
  jbd2: Check 'jh->b_transaction' before remove it from checkpoint

 fs/jbd2/checkpoint.c | 34 ++++++++++++++++------------------
 1 file changed, 16 insertions(+), 18 deletions(-)

-- 
2.39.2

[PATCH 1/3] jbd2: fix checkpoint cleanup performance regression

[Zhang Yi]

From: Zhang Yi <yi.zhang@huawei.com>

journal_clean_one_cp_list() has been merged into
journal_shrink_one_cp_list(), but do chekpoint buffer cleanup from the
committing process is just a best effort, it should stop scan once it
meet a busy buffer, or else it will cause a lot of invalid buffer scan
and checks. We catch a performance regression when doing fs_mark tests
below.

Test cmd:
 ./fs_mark  -d  scratch  -s  1024  -n  10000  -t  1  -D  100  -N  100

Before merging checkpoint buffer cleanup:
 FSUse%        Count         Size    Files/sec     App Overhead
     95        10000         1024       8304.9            49033

After merging checkpoint buffer cleanup:
 FSUse%        Count         Size    Files/sec     App Overhead
     95        10000         1024       7649.0            50012
 FSUse%        Count         Size    Files/sec     App Overhead
     95        10000         1024       2107.1            50871

After merging checkpoint buffer cleanup, the total loop count in
journal_shrink_one_cp_list() could be up to 6,261,600+ (50,000+ ~
100,000+ in general), most of them are invalid. This patch fix it
through passing 'shrink_type' into journal_shrink_one_cp_list() and add
a new 'SHRINK_BUSY_STOP' to indicate it should stop once meet a busy
buffer. After fix, the loop count descending back to 10,000+.

After this fix:
 FSUse%        Count         Size    Files/sec     App Overhead
     95        10000         1024       8558.4            49109

Fixes: b98dba273a0e ("jbd2: remove journal_clean_one_cp_list()")
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
 fs/jbd2/checkpoint.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index 9ec91017a7f3..936c6d758a65 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -349,6 +349,8 @@ int jbd2_cleanup_journal_tail(journal_t *journal)
 
 /* Checkpoint list management */
 
+enum shrink_type {SHRINK_DESTROY, SHRINK_BUSY_STOP, SHRINK_BUSY_SKIP};
+
 /*
  * journal_shrink_one_cp_list
  *
@@ -360,7 +362,8 @@ int jbd2_cleanup_journal_tail(journal_t *journal)
  * Called with j_list_lock held.
  */
 static unsigned long journal_shrink_one_cp_list(struct journal_head *jh,
-						bool destroy, bool *released)
+						enum shrink_type type,
+						bool *released)
 {
 	struct journal_head *last_jh;
 	struct journal_head *next_jh = jh;
@@ -376,12 +379,15 @@ static unsigned long journal_shrink_one_cp_list(struct journal_head *jh,
 		jh = next_jh;
 		next_jh = jh->b_cpnext;
 
-		if (destroy) {
+		if (type == SHRINK_DESTROY) {
 			ret = __jbd2_journal_remove_checkpoint(jh);
 		} else {
 			ret = jbd2_journal_try_remove_checkpoint(jh);
-			if (ret < 0)
-				continue;
+			if (ret < 0) {
+				if (type == SHRINK_BUSY_SKIP)
+					continue;
+				break;
+			}
 		}
 
 		nr_freed++;
@@ -445,7 +451,7 @@ unsigned long jbd2_journal_shrink_checkpoint_list(journal_t *journal,
 		tid = transaction->t_tid;
 
 		freed = journal_shrink_one_cp_list(transaction->t_checkpoint_list,
-						   false, &released);
+						   SHRINK_BUSY_SKIP, &released);
 		nr_freed += freed;
 		(*nr_to_scan) -= min(*nr_to_scan, freed);
 		if (*nr_to_scan == 0)
@@ -485,19 +491,21 @@ unsigned long jbd2_journal_shrink_checkpoint_list(journal_t *journal,
 void __jbd2_journal_clean_checkpoint_list(journal_t *journal, bool destroy)
 {
 	transaction_t *transaction, *last_transaction, *next_transaction;
+	enum shrink_type type;
 	bool released;
 
 	transaction = journal->j_checkpoint_transactions;
 	if (!transaction)
 		return;
 
+	type = destroy ? SHRINK_DESTROY : SHRINK_BUSY_STOP;
 	last_transaction = transaction->t_cpprev;
 	next_transaction = transaction;
 	do {
 		transaction = next_transaction;
 		next_transaction = transaction->t_cpnext;
 		journal_shrink_one_cp_list(transaction->t_checkpoint_list,
-					   destroy, &released);
+					   type, &released);
 		/*
 		 * This function only frees up some memory if possible so we
 		 * dont have an obligation to finish processing. Bail out if
-- 
2.39.2

[PATCH 2/3] jbd2: Check 'jh->b_transaction' before remove it from checkpoint

[Zhang Yi]

From: Zhihao Cheng <chengzhihao1@huawei.com>

Following process will corrupt ext4 image:
Step 1:
jbd2_journal_commit_transaction
 __jbd2_journal_insert_checkpoint(jh, commit_transaction)
 // Put jh into trans1->t_checkpoint_list
 journal->j_checkpoint_transactions = commit_transaction
 // Put trans1 into journal->j_checkpoint_transactions

Step 2:
do_get_write_access
 test_clear_buffer_dirty(bh) // clear buffer dirty，set jbd dirty
 __jbd2_journal_file_buffer(jh, transaction) // jh belongs to trans2

Step 3:
drop_cache
 journal_shrink_one_cp_list
  jbd2_journal_try_remove_checkpoint
   if (!trylock_buffer(bh))  // lock bh, true
   if (buffer_dirty(bh))     // buffer is not dirty
   __jbd2_journal_remove_checkpoint(jh)
   // remove jh from trans1->t_checkpoint_list

Step 4:
jbd2_log_do_checkpoint
 trans1 = journal->j_checkpoint_transactions
 // jh is not in trans1->t_checkpoint_list
 jbd2_cleanup_journal_tail(journal)  // trans1 is done

Step 5: Power cut, trans2 is not committed, jh is lost in next mounting.

Fix it by checking 'jh->b_transaction' before remove it from checkpoint.

Fixes: 46f881b5b175 ("jbd2: fix a race when checking checkpoint buffer busy")
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
 fs/jbd2/checkpoint.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index 936c6d758a65..f033ac807013 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -639,6 +639,8 @@ int jbd2_journal_try_remove_checkpoint(struct journal_head *jh)
 {
 	struct buffer_head *bh = jh2bh(jh);
 
+	if (jh->b_transaction)
+		return -EBUSY;
 	if (!trylock_buffer(bh))
 		return -EBUSY;
 	if (buffer_dirty(bh)) {
-- 
2.39.2

[PATCH 3/3] jbd2: remove unused function '__cp_buffer_busy'

[Zhang Yi]

From: Yang Li <yang.lee@linux.alibaba.com>

The code calling function '__cp_buffer_busy' has been removed, so the
function should also be removed.
silence the warning:
fs/jbd2/checkpoint.c:48:20: warning: unused function '__cp_buffer_busy'

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=5518
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 fs/jbd2/checkpoint.c | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index f033ac807013..118699fff2f9 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -40,18 +40,6 @@ static inline void __buffer_unlink(struct journal_head *jh)
 	}
 }
 
-/*
- * Check a checkpoint buffer could be release or not.
- *
- * Requires j_list_lock
- */
-static inline bool __cp_buffer_busy(struct journal_head *jh)
-{
-	struct buffer_head *bh = jh2bh(jh);
-
-	return (jh->b_transaction || buffer_locked(bh) || buffer_dirty(bh));
-}
-
 /*
  * __jbd2_log_wait_for_space: wait until there is space in the journal.
  *
-- 
2.39.2

Re: [PATCH 1/3] jbd2: fix checkpoint cleanup performance regression

[Jan Kara]

On Fri 14-07-23 10:55:26, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@huawei.com>
> 
> journal_clean_one_cp_list() has been merged into
> journal_shrink_one_cp_list(), but do chekpoint buffer cleanup from the
> committing process is just a best effort, it should stop scan once it
> meet a busy buffer, or else it will cause a lot of invalid buffer scan
> and checks. We catch a performance regression when doing fs_mark tests
> below.
> 
> Test cmd:
>  ./fs_mark  -d  scratch  -s  1024  -n  10000  -t  1  -D  100  -N  100
> 
> Before merging checkpoint buffer cleanup:
>  FSUse%        Count         Size    Files/sec     App Overhead
>      95        10000         1024       8304.9            49033
> 
> After merging checkpoint buffer cleanup:
>  FSUse%        Count         Size    Files/sec     App Overhead
>      95        10000         1024       7649.0            50012
>  FSUse%        Count         Size    Files/sec     App Overhead
>      95        10000         1024       2107.1            50871
> 
> After merging checkpoint buffer cleanup, the total loop count in
> journal_shrink_one_cp_list() could be up to 6,261,600+ (50,000+ ~
> 100,000+ in general), most of them are invalid. This patch fix it
> through passing 'shrink_type' into journal_shrink_one_cp_list() and add
> a new 'SHRINK_BUSY_STOP' to indicate it should stop once meet a busy
> buffer. After fix, the loop count descending back to 10,000+.
> 
> After this fix:
>  FSUse%        Count         Size    Files/sec     App Overhead
>      95        10000         1024       8558.4            49109
> 
> Fixes: b98dba273a0e ("jbd2: remove journal_clean_one_cp_list()")
> Signed-off-by: Zhang Yi <yi.zhang@huawei.com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  fs/jbd2/checkpoint.c | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
> index 9ec91017a7f3..936c6d758a65 100644
> --- a/fs/jbd2/checkpoint.c
> +++ b/fs/jbd2/checkpoint.c
> @@ -349,6 +349,8 @@ int jbd2_cleanup_journal_tail(journal_t *journal)
>  
>  /* Checkpoint list management */
>  
> +enum shrink_type {SHRINK_DESTROY, SHRINK_BUSY_STOP, SHRINK_BUSY_SKIP};
> +
>  /*
>   * journal_shrink_one_cp_list
>   *
> @@ -360,7 +362,8 @@ int jbd2_cleanup_journal_tail(journal_t *journal)
>   * Called with j_list_lock held.
>   */
>  static unsigned long journal_shrink_one_cp_list(struct journal_head *jh,
> -						bool destroy, bool *released)
> +						enum shrink_type type,
> +						bool *released)
>  {
>  	struct journal_head *last_jh;
>  	struct journal_head *next_jh = jh;
> @@ -376,12 +379,15 @@ static unsigned long journal_shrink_one_cp_list(struct journal_head *jh,
>  		jh = next_jh;
>  		next_jh = jh->b_cpnext;
>  
> -		if (destroy) {
> +		if (type == SHRINK_DESTROY) {
>  			ret = __jbd2_journal_remove_checkpoint(jh);
>  		} else {
>  			ret = jbd2_journal_try_remove_checkpoint(jh);
> -			if (ret < 0)
> -				continue;
> +			if (ret < 0) {
> +				if (type == SHRINK_BUSY_SKIP)
> +					continue;
> +				break;
> +			}
>  		}
>  
>  		nr_freed++;
> @@ -445,7 +451,7 @@ unsigned long jbd2_journal_shrink_checkpoint_list(journal_t *journal,
>  		tid = transaction->t_tid;
>  
>  		freed = journal_shrink_one_cp_list(transaction->t_checkpoint_list,
> -						   false, &released);
> +						   SHRINK_BUSY_SKIP, &released);
>  		nr_freed += freed;
>  		(*nr_to_scan) -= min(*nr_to_scan, freed);
>  		if (*nr_to_scan == 0)
> @@ -485,19 +491,21 @@ unsigned long jbd2_journal_shrink_checkpoint_list(journal_t *journal,
>  void __jbd2_journal_clean_checkpoint_list(journal_t *journal, bool destroy)
>  {
>  	transaction_t *transaction, *last_transaction, *next_transaction;
> +	enum shrink_type type;
>  	bool released;
>  
>  	transaction = journal->j_checkpoint_transactions;
>  	if (!transaction)
>  		return;
>  
> +	type = destroy ? SHRINK_DESTROY : SHRINK_BUSY_STOP;
>  	last_transaction = transaction->t_cpprev;
>  	next_transaction = transaction;
>  	do {
>  		transaction = next_transaction;
>  		next_transaction = transaction->t_cpnext;
>  		journal_shrink_one_cp_list(transaction->t_checkpoint_list,
> -					   destroy, &released);
> +					   type, &released);
>  		/*
>  		 * This function only frees up some memory if possible so we
>  		 * dont have an obligation to finish processing. Bail out if
> -- 
> 2.39.2
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH 2/3] jbd2: Check 'jh->b_transaction' before remove it from checkpoint

[Jan Kara]

On Fri 14-07-23 10:55:27, Zhang Yi wrote:
> From: Zhihao Cheng <chengzhihao1@huawei.com>
> 
> Following process will corrupt ext4 image:
> Step 1:
> jbd2_journal_commit_transaction
>  __jbd2_journal_insert_checkpoint(jh, commit_transaction)
>  // Put jh into trans1->t_checkpoint_list
>  journal->j_checkpoint_transactions = commit_transaction
>  // Put trans1 into journal->j_checkpoint_transactions
> 
> Step 2:
> do_get_write_access
>  test_clear_buffer_dirty(bh) // clear buffer dirty，set jbd dirty
>  __jbd2_journal_file_buffer(jh, transaction) // jh belongs to trans2
> 
> Step 3:
> drop_cache
>  journal_shrink_one_cp_list
>   jbd2_journal_try_remove_checkpoint
>    if (!trylock_buffer(bh))  // lock bh, true
>    if (buffer_dirty(bh))     // buffer is not dirty
>    __jbd2_journal_remove_checkpoint(jh)
>    // remove jh from trans1->t_checkpoint_list
> 
> Step 4:
> jbd2_log_do_checkpoint
>  trans1 = journal->j_checkpoint_transactions
>  // jh is not in trans1->t_checkpoint_list
>  jbd2_cleanup_journal_tail(journal)  // trans1 is done
> 
> Step 5: Power cut, trans2 is not committed, jh is lost in next mounting.
> 
> Fix it by checking 'jh->b_transaction' before remove it from checkpoint.
> 
> Fixes: 46f881b5b175 ("jbd2: fix a race when checking checkpoint buffer busy")
> Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
> Signed-off-by: Zhang Yi <yi.zhang@huawei.com>

Indeed! I've missed this difference between __cp_buffer_busy() and
jbd2_journal_try_remove_checkpoint() during my review of 46f881b5b175. The
fix looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  fs/jbd2/checkpoint.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
> index 936c6d758a65..f033ac807013 100644
> --- a/fs/jbd2/checkpoint.c
> +++ b/fs/jbd2/checkpoint.c
> @@ -639,6 +639,8 @@ int jbd2_journal_try_remove_checkpoint(struct journal_head *jh)
>  {
>  	struct buffer_head *bh = jh2bh(jh);
>  
> +	if (jh->b_transaction)
> +		return -EBUSY;
>  	if (!trylock_buffer(bh))
>  		return -EBUSY;
>  	if (buffer_dirty(bh)) {
> -- 
> 2.39.2
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH 0/3] jbd2: some fixes and cleanup about "jbd2: fix several checkpoint inconsistent issues"

[Theodore Ts'o]

On Fri, 14 Jul 2023 10:55:25 +0800, Zhang Yi wrote:
> These patch set includes 2 fixes and 1 cleanup about "jbd2: fix several
> checkpoint inconsistent issues" patch set[1] recently applied in dev
> branch. The first patch fix a performance regression introduced while
> merging journal_shrink_one_cp_list(). The second one add a missing
> check before dropping checkpoint buffer that could lead to filesystem
> inconsistent. The last patch which is from Yang Li, remove the unused
> __cp_buffer_busy() helper. Please see the corresponding patch for
> details.
> 
> [...]

Applied, thanks!

[1/3] jbd2: fix checkpoint cleanup performance regression
      commit: 373ac521799d9e97061515aca6ec6621789036bb
[2/3] jbd2: Check 'jh->b_transaction' before remove it from checkpoint
      commit: 590a809ff743e7bd890ba5fb36bc38e20a36de53
[3/3] jbd2: remove unused function '__cp_buffer_busy'
      commit: 5f02a30eac5cc1c081cbdb42d19fd0ded00b0618

Best regards,
-- 
Theodore Ts'o <tytso@mit.edu>