Re:Re: [PATCH v5 1/2] f2fs: introduce proc/fs/f2fs/<dev>/fsck_stack node

[李扬韬]

From: Chao Yu <chao@xxxxxxxxxx>
Date: 2021-08-13 22:44:49
To:  Yangtao Li <frank.li@xxxxxxxx>,jaegeuk@xxxxxxxxxx
Cc:  linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx,linux-kernel@xxxxxxxxxxxxxxx
Subject: Re: [PATCH v5 1/2] f2fs: introduce proc/fs/f2fs/<dev>/fsck_stack node>On 2021/8/13 20:32, Yangtao Li wrote:
>> SBI_NEED_FSCK is an indicator that fsck.f2fs needs to be triggered,
>> this flag is set in too many places. For some scenes that are not very
>> reproducible, adding stack information will help locate the problem.
>> 
>> Let's expose all fsck stack history in procfs.
>> 
>> Signed-off-by: Yangtao Li <frank.li@xxxxxxxx>
>> ---
>> v5:
>> -fix implicit declaration of function 'stack_trace_save'
>>   fs/f2fs/f2fs.h  | 34 +++++++++++++++++++++++++++++++++-
>>   fs/f2fs/sysfs.c | 26 ++++++++++++++++++++++++++
>>   2 files changed, 59 insertions(+), 1 deletion(-)
>> 
>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>> index 67faa43cc141..cbd06dea3c6a 100644
>> --- a/fs/f2fs/f2fs.h
>> +++ b/fs/f2fs/f2fs.h
>> @@ -24,6 +24,8 @@
>>   #include <linux/quotaops.h>
>>   #include <linux/part_stat.h>
>>   #include <crypto/hash.h>
>> +#include <linux/stackdepot.h>
>> +#include <linux/stacktrace.h>
>>   
>>   #include <linux/fscrypt.h>
>>   #include <linux/fsverity.h>
>> @@ -119,6 +121,8 @@ typedef u32 nid_t;
>>   
>>   #define COMPRESS_EXT_NUM		16
>>   
>> +#define FSCK_STACK_DEPTH 64
>> +
>>   struct f2fs_mount_info {
>>   	unsigned int opt;
>>   	int write_io_size_bits;		/* Write IO size bits */
>> @@ -1786,6 +1790,8 @@ struct f2fs_sb_info {
>>   	unsigned int compress_watermark;	/* cache page watermark */
>>   	atomic_t compress_page_hit;		/* cache hit count */
>>   #endif
>> +	depot_stack_handle_t *fsck_stack;
>> +	unsigned int fsck_count;
>>   };
>>   
>>   struct f2fs_private_dio {
>> @@ -1997,9 +2003,35 @@ static inline bool is_sbi_flag_set(struct f2fs_sb_info *sbi, unsigned int type)
>>   	return test_bit(type, &sbi->s_flag);
>>   }
>>   
>> -static inline void set_sbi_flag(struct f2fs_sb_info *sbi, unsigned int type)
>> +static void set_sbi_flag(struct f2fs_sb_info *sbi, unsigned int type)
>>   {
>>   	set_bit(type, &sbi->s_flag);
>> +
>> +	if (unlikely(type ==  SBI_NEED_FSCK)) {
>
>Hmm... I don't know what to say...

Sorry, maybe there is a problem with my vim configuration.
The strange thing is that checkpatch.pl didn't check it out.

>
>> +		unsigned long entries[FSCK_STACK_DEPTH];
>> +		depot_stack_handle_t stack, *new;
>> +		unsigned int nr_entries;
>> +		int i;
>> +
>> +		nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
>> +		nr_entries = filter_irq_stacks(entries, nr_entries);
>> +		stack = stack_depot_save(entries, nr_entries, GFP_KERNEL);
>> +		if (!stack)
>> +			return;
>> +
>> +		/* Try to find an existing entry for this backtrace */
>> +		for (i = 0; i < sbi->fsck_count; i++)
>> +			if (sbi->fsck_stack[i] == stack)
>
>stack need to be released here?

We can't remove stack from depot, as we store them contiguously one after
another in a contiguous memory allocation.

Or we can limit the recorded stack number.

$ grep -nr "SBI_NEED_FSCK" fs/f2fs/ --include=*.c --include=*.h | wc -l
53
$ grep -nr "f2fs_bug_on" fs/f2fs/ --include=*.c --include=*.h | wc -l
135

Since we only have two hundred possible settings here, considering that
the same stack will not be recorded, and the probability of occurrence will
not be high, so it is acceptable not to release?

If this is the case, the subsequent allocation does not need to be released.

Thx,
Yangtao