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Date: Thu, 19 Aug 2021 16:04:15 +0800
From: Chao Yu <chao@...nel.org>
To: 李扬韬 <frank.li@...o.com>
Cc: jaegeuk@...nel.org, linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6] f2fs: introduce /sys/fs/f2fs/<disk>/fsck_stack node
On 2021/8/16 15:23, 李扬韬 wrote:
>>> HI Chao,
>>>>> 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 record all fsck stack history, I added F2FS_FSCK_STACK_TRACE
>>>>> configuration options and sysfs nodes. After opening the configuration
>>>>> options and enabling the node, it will start recording. The recorded
>>>>> stack information will not be clear, and we can get information form
>>>>> kernel log.
>>>>>
>>>>> Signed-off-by: Yangtao Li <frank.li@...o.com>
>>>>> ---
>>>>> Documentation/ABI/testing/sysfs-fs-f2fs | 7 ++++
>>>>> fs/f2fs/Kconfig | 10 ++++++
>>>>> fs/f2fs/f2fs.h | 45 +++++++++++++++++++++++++
>>>>> fs/f2fs/sysfs.c | 27 +++++++++++++++
>>>>> 4 files changed, 89 insertions(+)
>>>>>
>>>>> diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
>>>>> index ef4b9218ae1e..047c398093cf 100644
>>>>> --- a/Documentation/ABI/testing/sysfs-fs-f2fs
>>>>> +++ b/Documentation/ABI/testing/sysfs-fs-f2fs
>>>>> @@ -493,3 +493,10 @@ Contact: "Chao Yu" <yuchao0@...wei.com>
>>>>> Description: When ATGC is on, it controls age threshold to bypass GCing young
>>>>> candidates whose age is not beyond the threshold, by default it was
>>>>> initialized as 604800 seconds (equals to 7 days).
>>>>> +
>>>>> +What: /sys/fs/f2fs/<disk>/fsck_stack
>>>>> +Date: August 2021
>>>>> +Contact: "Yangtao Li" <frank.li@...o.com>
>>>>> +Description: Controls to enable/disable fsck stack trace, you can get stack
>>>>> + information from kernel log. Note that the recorded stack information
>>>>> + will not be cleared.
>>>>
>>>> Again, please don't add this into sysfs.
>>
>>Oh, I missed to check the details...
>>
>>>
>>> I added this node, part of the idea is to trigger the export of stack information.
>>> There is no information transmitted through sysfs here, but the record of the stack is switched on and off.
>>> If don't export this information through procfs and sysfs, is there a more appropriate way?
>>
>>Well, I doubt why we should export stack info via proc/sysfs node or
>>sysfs switch.
>>
>>Those info will always be needed to troubleshoot issues no matter in
>>user or eng version of Android, can we just print them directly into
>>kernel message... what I concern is we may lost the bug scene due to
>>no one can help to trigger dmesg printing via sysfs.
>>
>>Jaegeuk, thoughts?
>>
>>>
>>>>
>>>>> diff --git a/fs/f2fs/Kconfig b/fs/f2fs/Kconfig
>>>>> index 7669de7b49ce..f451e567e4a8 100644
>>>>> --- a/fs/f2fs/Kconfig
>>>>> +++ b/fs/f2fs/Kconfig
>>>>> @@ -135,3 +135,13 @@ config F2FS_FS_LZORLE
>>>>> default y
>>>>> help
>>>>> Support LZO-RLE compress algorithm, if unsure, say Y.
>>>>> +
>>>>> +config F2FS_FSCK_STACK_TRACE
>>>>
>>>> I don't think we need another config to wrap this functionality, may be we
>>>> can use F2FS_CHECK_FS instead.
>>>
>>> OK.
>>>
>>>>
>>>>> + bool "F2FS fsck stack information record"
>>>>> + depends on F2FS_FS
>>>>> + depends on STACKDEPOT
>>>>> + default y
>>>>> + help
>>>>> + Support printing out fsck stack history. With this, you have to
>>>>> + turn on "fsck_stack" sysfs node. Then you can get information
>>>>> + from kernel log.
>>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>>> index ee8eb33e2c25..b2d1d1a5a3fc 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>
>>>>> @@ -117,6 +119,8 @@ typedef u32 nid_t;
>>>>>
>>>>> #define COMPRESS_EXT_NUM 16
>>>>>
>>>>> +#define FSCK_STACK_DEPTH 64
>>>>
>>>> 16?
>>>
>>> OK.
>>>
>>>>
>>>>> +
>>>>> struct f2fs_mount_info {
>>>>> unsigned int opt;
>>>>> int write_io_size_bits; /* Write IO size bits */
>>>>> @@ -1748,6 +1752,11 @@ struct f2fs_sb_info {
>>>>> unsigned int compress_watermark; /* cache page watermark */
>>>>> atomic_t compress_page_hit; /* cache hit count */
>>>>> #endif
>>>>> +#ifdef CONFIG_F2FS_FSCK_STACK_TRACE
>>>>> + depot_stack_handle_t *fsck_stack_history;
>>>>> + unsigned int fsck_count;
>>>>> + bool fsck_stack;
>>>>
>>>> IMO, all bug_on()s are corner cases, and catching those stacks won't cost
>>>> much, so we can just use CONFIG_XXX to enable/disable this feature.
>>>
>>> F2FS_CHECK_FS ？
>>>
>>>>
>>>>> +#endif
>>>>> };
>>>>>
>>>>> struct f2fs_private_dio {
>>>>> @@ -1954,6 +1963,38 @@ static inline struct address_space *NODE_MAPPING(struct f2fs_sb_info *sbi)
>>>>> return sbi->node_inode->i_mapping;
>>>>> }
>>>>>
>>>>> +#ifdef CONFIG_F2FS_FSCK_STACK_TRACE
>>>>> +static void fsck_stack_trace(struct f2fs_sb_info *sbi)
>>>>> +{
>>>>> + unsigned long entries[FSCK_STACK_DEPTH];
>>>>> + depot_stack_handle_t stack, *new;
>>>>> + unsigned int nr_entries;
>>>>> + int i;
>>>>> +
>>>>> + if (!sbi->fsck_stack)
>>>>> + return;
>>>>> +
>>>>> + 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_history[i] == stack)
>>>>> + return;
>>>>> +
>>>>> + new = krealloc(sbi->fsck_stack_history, (sbi->fsck_count + 1) *
>>>>> + sizeof(*sbi->fsck_stack_history), GFP_KERNEL);
>>>>> + if (!new)
>>>>> + return;
>>>>> +
>>>>> + sbi->fsck_stack_history = new;
>>>>> + sbi->fsck_stack_history[sbi->fsck_count++] = stack;
>>>>
>>>> It will case memory leak after f2fs module exits.
>>>
>>> So let's enable this feature when f2fs is not a module and enable F2FS_CHECK_FS.
>>
>>I mean it needs to free .fsck_stack_history during umount().
> >
>
> So this is a double-edged sword, and the person who uses it must be aware of this issue.
> The release seems unrealistic under the current circumstances. This is also the reason
You mean the handles allocated from stack_depot_save() should not be released, right?
> why I add a switch, instead of enabling it by default after opening the configuration.
Well, I still didn't get why we can not release the memory allocated by krealloc().
Thanks,
>
> Yangtao
>
>
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