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SubjectRe: [PATCH v5 1/2] f2fs: introduce proc/fs/f2fs/<dev>/fsck_stack node
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On 2021/8/14 2:33, 李扬韬 wrote:
> From: Chao Yu <chao@kernel.org>
> Date: 2021-08-13 22:44:49
> To: Yangtao Li <frank.li@vivo.com>,jaegeuk@kernel.org
> Cc: linux-f2fs-devel@lists.sourceforge.net,linux-kernel@vger.kernel.org
> 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@vivo.com>
>>> ---
>>> 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

I didn't look into details of stack_depot_save(), two stack handles from below
call paths will be the same?

- move_data_block
- f2fs_wait_on_page_writeback
- f2fs_bug_on

- ra_data_block
- f2fs_wait_on_page_writeback
- f2fs_bug_on

If they have different stack handles, combination number of
set_sbi_flag(NEED_FSCK)/f2fs_bug_on and their callers will be far more than two
hundred.

Thanks,

>
> 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
>

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