When z_erofs_read_folio() reads a page with an offset far beyond EOF, two
issues may occur:
- z_erofs_pcluster_readmore() may take a long time to loop when the offset
  is big enough, which is unnecessary.
    - For example, it will loop 4691368 times and take about 27 seconds
      with following case.
        - offset = 19217289215
        - inode_size = 1442672
- z_erofs_do_read_page() may loop infinitely due to the inappropriate
  truncation in the below statement. Since the offset is 64 bits and
min_t() truncates the result to 32 bits. The solution is to replace
unsigned int with another 64-bit type, such as erofs_off_t.
    cur = end - min_t(unsigned int, offset + end - map->m_la, end);
    - For example:
        - offset = 0x400160000
        - end = 0x370
        - map->m_la = 0x160370
        - offset + end - map->m_la = 0x400000000
        - offset + end - map->m_la = 0x00000000 (truncated as unsigned int)
    - Expected result:
        - cur = 0
    - Actual result:
        - cur = 0x370

Signed-off-by: Chunhai Guo <guochunhai@vivo.com>
---
 fs/erofs/zdata.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 5f1890e309c6..6abbd4510076 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -972,7 +972,8 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
 	struct erofs_map_blocks *const map = &fe->map;
 	const loff_t offset = page_offset(page);
 	bool tight = true, exclusive;
-	unsigned int cur, end, spiltted;
+	erofs_off_t cur, end;
+	unsigned int spiltted;
 	int err = 0;
 
 	/* register locked file pages as online pages in pack */
@@ -1035,7 +1036,7 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
 	 */
 	tight &= (fe->mode > Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE);
 
-	cur = end - min_t(unsigned int, offset + end - map->m_la, end);
+	cur = end - min_t(erofs_off_t, offset + end - map->m_la, end);
 	if (!(map->m_flags & EROFS_MAP_MAPPED)) {
 		zero_user_segment(page, cur, end);
 		goto next_part;
@@ -1841,7 +1842,7 @@ static void z_erofs_pcluster_readmore(struct z_erofs_decompress_frontend *f,
 	}
 
 	cur = map->m_la + map->m_llen - 1;
-	while (cur >= end) {
+	while ((cur >= end) && (cur < i_size_read(inode))) {
 		pgoff_t index = cur >> PAGE_SHIFT;
 		struct page *page;
 
@@ -1876,6 +1877,12 @@ static int z_erofs_read_folio(struct file *file, struct folio *folio)
 	trace_erofs_readpage(page, false);
 	f.headoffset = (erofs_off_t)page->index << PAGE_SHIFT;
 
+	/* when trying to read beyond EOF, return zero page directly */
+	if (f.headoffset >= i_size_read(inode)) {
+		zero_user_segment(page, 0, PAGE_SIZE);
+		return 0;
+	}
+
 	z_erofs_pcluster_readmore(&f, NULL, true);
 	err = z_erofs_do_read_page(&f, page);
 	z_erofs_pcluster_readmore(&f, NULL, false);
-- 
2.25.1

Hi Chunhai,

On 2023/7/8 14:24, Chunhai Guo wrote:
> When z_erofs_read_folio() reads a page with an offset far beyond EOF, two
> issues may occur:
> - z_erofs_pcluster_readmore() may take a long time to loop when the offset
>    is big enough, which is unnecessary.
>      - For example, it will loop 4691368 times and take about 27 seconds
>        with following case.
>          - offset = 19217289215
>          - inode_size = 1442672
> - z_erofs_do_read_page() may loop infinitely due to the inappropriate
>    truncation in the below statement. Since the offset is 64 bits and
> min_t() truncates the result to 32 bits. The solution is to replace
> unsigned int with another 64-bit type, such as erofs_off_t.
>      cur = end - min_t(unsigned int, offset + end - map->m_la, end);
>      - For example:
>          - offset = 0x400160000
>          - end = 0x370
>          - map->m_la = 0x160370
>          - offset + end - map->m_la = 0x400000000
>          - offset + end - map->m_la = 0x00000000 (truncated as unsigned int)

Thanks for the catch!

Could you split these two into two patches?

how about using:
cur = end - min_t(erofs_off_t, offend + end - map->m_la, end)
for this?

since cur and end are all [0, PAGE_SIZE - 1] for now, and
folio_size() later.

>      - Expected result:
>          - cur = 0
>      - Actual result:
>          - cur = 0x370
> 
> Signed-off-by: Chunhai Guo <guochunhai@vivo.com>
> ---
>   fs/erofs/zdata.c | 13 ++++++++++---
>   1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> index 5f1890e309c6..6abbd4510076 100644
> --- a/fs/erofs/zdata.c
> +++ b/fs/erofs/zdata.c
> @@ -972,7 +972,8 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
>   	struct erofs_map_blocks *const map = &fe->map;
>   	const loff_t offset = page_offset(page);
>   	bool tight = true, exclusive;
> -	unsigned int cur, end, spiltted;
> +	erofs_off_t cur, end;
> +	unsigned int spiltted;
>   	int err = 0;
>   
>   	/* register locked file pages as online pages in pack */
> @@ -1035,7 +1036,7 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
>   	 */
>   	tight &= (fe->mode > Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE);
>   
> -	cur = end - min_t(unsigned int, offset + end - map->m_la, end);
> +	cur = end - min_t(erofs_off_t, offset + end - map->m_la, end);
>   	if (!(map->m_flags & EROFS_MAP_MAPPED)) {
>   		zero_user_segment(page, cur, end);
>   		goto next_part;
> @@ -1841,7 +1842,7 @@ static void z_erofs_pcluster_readmore(struct z_erofs_decompress_frontend *f,
>   	}
>   
>   	cur = map->m_la + map->m_llen - 1;
> -	while (cur >= end) {
> +	while ((cur >= end) && (cur < i_size_read(inode))) {
>   		pgoff_t index = cur >> PAGE_SHIFT;
>   		struct page *page;
>   
> @@ -1876,6 +1877,12 @@ static int z_erofs_read_folio(struct file *file, struct folio *folio)
>   	trace_erofs_readpage(page, false);
>   	f.headoffset = (erofs_off_t)page->index << PAGE_SHIFT;
>   
> +	/* when trying to read beyond EOF, return zero page directly */
> +	if (f.headoffset >= i_size_read(inode)) {
> +		zero_user_segment(page, 0, PAGE_SIZE);
> +		return 0;
> +	}
Do we really need to optimize this rare case?
I guess the follow readmore fix is enough, thoughts?


Thanks,
Gao Xiang

Hi Xiang,

On 2023/7/8 17:00, Gao Xiang wrote:
> Hi Chunhai,
> 
> On 2023/7/8 14:24, Chunhai Guo wrote:
>> When z_erofs_read_folio() reads a page with an offset far beyond EOF, two
>> issues may occur:
>> - z_erofs_pcluster_readmore() may take a long time to loop when the offset
>>     is big enough, which is unnecessary.
>>       - For example, it will loop 4691368 times and take about 27 seconds
>>         with following case.
>>           - offset = 19217289215
>>           - inode_size = 1442672
>> - z_erofs_do_read_page() may loop infinitely due to the inappropriate
>>     truncation in the below statement. Since the offset is 64 bits and
>> min_t() truncates the result to 32 bits. The solution is to replace
>> unsigned int with another 64-bit type, such as erofs_off_t.
>>       cur = end - min_t(unsigned int, offset + end - map->m_la, end);
>>       - For example:
>>           - offset = 0x400160000
>>           - end = 0x370
>>           - map->m_la = 0x160370
>>           - offset + end - map->m_la = 0x400000000
>>           - offset + end - map->m_la = 0x00000000 (truncated as unsigned int)
> 
> Thanks for the catch!
> 
> Could you split these two into two patches?
> 
> how about using:
> cur = end - min_t(erofs_off_t, offend + end - map->m_la, end)
> for this?
> 
> since cur and end are all [0, PAGE_SIZE - 1] for now, and
> folio_size() later.

OK. I will split the patch.

Sorry that I can not understand what is 'offend' refer to and what do 
you mean. Could you please describe it more clearly?

>>       - Expected result:
>>           - cur = 0
>>       - Actual result:
>>           - cur = 0x370
>>
>> Signed-off-by: Chunhai Guo <guochunhai@vivo.com>
>> ---
>>    fs/erofs/zdata.c | 13 ++++++++++---
>>    1 file changed, 10 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
>> index 5f1890e309c6..6abbd4510076 100644
>> --- a/fs/erofs/zdata.c
>> +++ b/fs/erofs/zdata.c
>> @@ -972,7 +972,8 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
>>    	struct erofs_map_blocks *const map = &fe->map;
>>    	const loff_t offset = page_offset(page);
>>    	bool tight = true, exclusive;
>> -	unsigned int cur, end, spiltted;
>> +	erofs_off_t cur, end;
>> +	unsigned int spiltted;
>>    	int err = 0;
>>    
>>    	/* register locked file pages as online pages in pack */
>> @@ -1035,7 +1036,7 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
>>    	 */
>>    	tight &= (fe->mode > Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE);
>>    
>> -	cur = end - min_t(unsigned int, offset + end - map->m_la, end);
>> +	cur = end - min_t(erofs_off_t, offset + end - map->m_la, end);
>>    	if (!(map->m_flags & EROFS_MAP_MAPPED)) {
>>    		zero_user_segment(page, cur, end);
>>    		goto next_part;
>> @@ -1841,7 +1842,7 @@ static void z_erofs_pcluster_readmore(struct z_erofs_decompress_frontend *f,
>>    	}
>>    
>>    	cur = map->m_la + map->m_llen - 1;
>> -	while (cur >= end) {
>> +	while ((cur >= end) && (cur < i_size_read(inode))) {
>>    		pgoff_t index = cur >> PAGE_SHIFT;
>>    		struct page *page;
>>    
>> @@ -1876,6 +1877,12 @@ static int z_erofs_read_folio(struct file *file, struct folio *folio)
>>    	trace_erofs_readpage(page, false);
>>    	f.headoffset = (erofs_off_t)page->index << PAGE_SHIFT;
>>    
>> +	/* when trying to read beyond EOF, return zero page directly */
>> +	if (f.headoffset >= i_size_read(inode)) {
>> +		zero_user_segment(page, 0, PAGE_SIZE);
>> +		return 0;
>> +	}
> Do we really need to optimize this rare case?
> I guess the follow readmore fix is enough, thoughts? >
> Thanks,
> Gao Xiang

Since the code is constantly being updated and someone may encounter 
this bug again, I think we had better fix it if possible.

Thanks.
Guo Chunhai

On 2023/7/10 11:32, Chunhai Guo wrote:
> Hi Xiang,
> 
> On 2023/7/8 17:00, Gao Xiang wrote:
>> Hi Chunhai,
>>
>> On 2023/7/8 14:24, Chunhai Guo wrote:
>>> When z_erofs_read_folio() reads a page with an offset far beyond EOF, two
>>> issues may occur:
>>> - z_erofs_pcluster_readmore() may take a long time to loop when the offset
>>>     is big enough, which is unnecessary.
>>>       - For example, it will loop 4691368 times and take about 27 seconds
>>>         with following case.
>>>           - offset = 19217289215
>>>           - inode_size = 1442672
>>> - z_erofs_do_read_page() may loop infinitely due to the inappropriate
>>>     truncation in the below statement. Since the offset is 64 bits and
>>> min_t() truncates the result to 32 bits. The solution is to replace
>>> unsigned int with another 64-bit type, such as erofs_off_t.
>>>       cur = end - min_t(unsigned int, offset + end - map->m_la, end);
>>>       - For example:
>>>           - offset = 0x400160000
>>>           - end = 0x370
>>>           - map->m_la = 0x160370
>>>           - offset + end - map->m_la = 0x400000000
>>>           - offset + end - map->m_la = 0x00000000 (truncated as unsigned int)
>>
>> Thanks for the catch!
>>
>> Could you split these two into two patches?
>>
>> how about using:
>> cur = end - min_t(erofs_off_t, offend + end - map->m_la, end)
>> for this?
>>
>> since cur and end are all [0, PAGE_SIZE - 1] for now, and
>> folio_size() later.
> 
> OK. I will split the patch.
> 
> Sorry that I can not understand what is 'offend' refer to and what do you mean. Could you please describe it more clearly?

Sorry, there is a typo here, I meant 'offset'.

`cur` and `end` both are not exceed 4096 if your page_size
is 4096.

Does
cur = end - min_t(erofs_off_t, offset + end - map->m_la, end)

fix your issue?

> 
>>>       - Expected result:
>>>           - cur = 0
>>>       - Actual result:
>>>           - cur = 0x370
>>>
>>> Signed-off-by: Chunhai Guo <guochunhai@vivo.com>
>>> ---
>>>    fs/erofs/zdata.c | 13 ++++++++++---
>>>    1 file changed, 10 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
>>> index 5f1890e309c6..6abbd4510076 100644
>>> --- a/fs/erofs/zdata.c
>>> +++ b/fs/erofs/zdata.c
>>> @@ -972,7 +972,8 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
>>>        struct erofs_map_blocks *const map = &fe->map;
>>>        const loff_t offset = page_offset(page);
>>>        bool tight = true, exclusive;
>>> -    unsigned int cur, end, spiltted;
>>> +    erofs_off_t cur, end;
>>> +    unsigned int spiltted;
>>>        int err = 0;
>>>        /* register locked file pages as online pages in pack */
>>> @@ -1035,7 +1036,7 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
>>>         */
>>>        tight &= (fe->mode > Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE);
>>> -    cur = end - min_t(unsigned int, offset + end - map->m_la, end);
>>> +    cur = end - min_t(erofs_off_t, offset + end - map->m_la, end);
>>>        if (!(map->m_flags & EROFS_MAP_MAPPED)) {
>>>            zero_user_segment(page, cur, end);
>>>            goto next_part;
>>> @@ -1841,7 +1842,7 @@ static void z_erofs_pcluster_readmore(struct z_erofs_decompress_frontend *f,
>>>        }
>>>        cur = map->m_la + map->m_llen - 1;
>>> -    while (cur >= end) {
>>> +    while ((cur >= end) && (cur < i_size_read(inode))) {
>>>            pgoff_t index = cur >> PAGE_SHIFT;
>>>            struct page *page;
>>> @@ -1876,6 +1877,12 @@ static int z_erofs_read_folio(struct file *file, struct folio *folio)
>>>        trace_erofs_readpage(page, false);
>>>        f.headoffset = (erofs_off_t)page->index << PAGE_SHIFT;
>>> +    /* when trying to read beyond EOF, return zero page directly */
>>> +    if (f.headoffset >= i_size_read(inode)) {
>>> +        zero_user_segment(page, 0, PAGE_SIZE);
>>> +        return 0;
>>> +    }
>> Do we really need to optimize this rare case?
>> I guess the follow readmore fix is enough, thoughts? >
>> Thanks,
>> Gao Xiang
> 
> Since the code is constantly being updated and someone may encounter this bug again, I think we had better fix it if possible.

z_erofs_do_read_page() already covers this case so I'm
not sure why we need to add another logic here.

Thanks,
Gao Xiang

> 
> Thanks.
> Guo Chunhai

On 2023/7/10 11:37, Gao Xiang wrote:
> 
> 
> On 2023/7/10 11:32, Chunhai Guo wrote:
>> Hi Xiang,
>>
>> On 2023/7/8 17:00, Gao Xiang wrote:
>>> Hi Chunhai,
>>>
>>> On 2023/7/8 14:24, Chunhai Guo wrote:
>>>> When z_erofs_read_folio() reads a page with an offset far beyond EOF, two
>>>> issues may occur:
>>>> - z_erofs_pcluster_readmore() may take a long time to loop when the offset
>>>>      is big enough, which is unnecessary.
>>>>        - For example, it will loop 4691368 times and take about 27 seconds
>>>>          with following case.
>>>>            - offset = 19217289215
>>>>            - inode_size = 1442672
>>>> - z_erofs_do_read_page() may loop infinitely due to the inappropriate
>>>>      truncation in the below statement. Since the offset is 64 bits and
>>>> min_t() truncates the result to 32 bits. The solution is to replace
>>>> unsigned int with another 64-bit type, such as erofs_off_t.
>>>>        cur = end - min_t(unsigned int, offset + end - map->m_la, end);
>>>>        - For example:
>>>>            - offset = 0x400160000
>>>>            - end = 0x370
>>>>            - map->m_la = 0x160370
>>>>            - offset + end - map->m_la = 0x400000000
>>>>            - offset + end - map->m_la = 0x00000000 (truncated as unsigned int)
>>>
>>> Thanks for the catch!
>>>
>>> Could you split these two into two patches?
>>>
>>> how about using:
>>> cur = end - min_t(erofs_off_t, offend + end - map->m_la, end)
>>> for this?
>>>
>>> since cur and end are all [0, PAGE_SIZE - 1] for now, and
>>> folio_size() later.
>>
>> OK. I will split the patch.
>>
>> Sorry that I can not understand what is 'offend' refer to and what do you mean. Could you please describe it more clearly?
> 
> Sorry, there is a typo here, I meant 'offset'.
> 
> `cur` and `end` both are not exceed 4096 if your page_size
> is 4096.
> 
> Does
> cur = end - min_t(erofs_off_t, offset + end - map->m_la, end)
> 
> fix your issue?

Yes. I think this will fix this issue. Do you mean the below change is 
unncessary?
 >>>> -    unsigned int cur, end, spiltted;
 >>>> +    erofs_off_t cur, end;
 >>>> +    unsigned int spiltted;

> 
>>
>>>>        - Expected result:
>>>>            - cur = 0
>>>>        - Actual result:
>>>>            - cur = 0x370
>>>>
>>>> Signed-off-by: Chunhai Guo <guochunhai@vivo.com>
>>>> ---
>>>>     fs/erofs/zdata.c | 13 ++++++++++---
>>>>     1 file changed, 10 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
>>>> index 5f1890e309c6..6abbd4510076 100644
>>>> --- a/fs/erofs/zdata.c
>>>> +++ b/fs/erofs/zdata.c
>>>> @@ -972,7 +972,8 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
>>>>         struct erofs_map_blocks *const map = &fe->map;
>>>>         const loff_t offset = page_offset(page);
>>>>         bool tight = true, exclusive;
>>>> -    unsigned int cur, end, spiltted;
>>>> +    erofs_off_t cur, end;
>>>> +    unsigned int spiltted;
>>>>         int err = 0;
>>>>         /* register locked file pages as online pages in pack */
>>>> @@ -1035,7 +1036,7 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
>>>>          */
>>>>         tight &= (fe->mode > Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE);
>>>> -    cur = end - min_t(unsigned int, offset + end - map->m_la, end);
>>>> +    cur = end - min_t(erofs_off_t, offset + end - map->m_la, end);
>>>>         if (!(map->m_flags & EROFS_MAP_MAPPED)) {
>>>>             zero_user_segment(page, cur, end);
>>>>             goto next_part;
>>>> @@ -1841,7 +1842,7 @@ static void z_erofs_pcluster_readmore(struct z_erofs_decompress_frontend *f,
>>>>         }
>>>>         cur = map->m_la + map->m_llen - 1;
>>>> -    while (cur >= end) {
>>>> +    while ((cur >= end) && (cur < i_size_read(inode))) {
>>>>             pgoff_t index = cur >> PAGE_SHIFT;
>>>>             struct page *page;
>>>> @@ -1876,6 +1877,12 @@ static int z_erofs_read_folio(struct file *file, struct folio *folio)
>>>>         trace_erofs_readpage(page, false);
>>>>         f.headoffset = (erofs_off_t)page->index << PAGE_SHIFT;
>>>> +    /* when trying to read beyond EOF, return zero page directly */
>>>> +    if (f.headoffset >= i_size_read(inode)) {
>>>> +        zero_user_segment(page, 0, PAGE_SIZE);
>>>> +        return 0;
>>>> +    }
>>> Do we really need to optimize this rare case?
>>> I guess the follow readmore fix is enough, thoughts? >
>>> Thanks,
>>> Gao Xiang
>>
>> Since the code is constantly being updated and someone may encounter this bug again, I think we had better fix it if possible.
> 
> z_erofs_do_read_page() already covers this case so I'm
> not sure why we need to add another logic here.

You are right. I have removed this logic and sent the patch.

> 
> Thanks,
> Gao Xiang
> 
>>
>> Thanks.
>> Guo Chunhai

On 2023/7/10 12:35, Chunhai Guo wrote:
> 
> 
> On 2023/7/10 11:37, Gao Xiang wrote:
>>
>>
>> On 2023/7/10 11:32, Chunhai Guo wrote:
>>> Hi Xiang,
>>>
>>> On 2023/7/8 17:00, Gao Xiang wrote:
>>>> Hi Chunhai,
>>>>
>>>> On 2023/7/8 14:24, Chunhai Guo wrote:
>>>>> When z_erofs_read_folio() reads a page with an offset far beyond EOF, two
>>>>> issues may occur:
>>>>> - z_erofs_pcluster_readmore() may take a long time to loop when the offset
>>>>>      is big enough, which is unnecessary.
>>>>>        - For example, it will loop 4691368 times and take about 27 seconds
>>>>>          with following case.
>>>>>            - offset = 19217289215
>>>>>            - inode_size = 1442672
>>>>> - z_erofs_do_read_page() may loop infinitely due to the inappropriate
>>>>>      truncation in the below statement. Since the offset is 64 bits and
>>>>> min_t() truncates the result to 32 bits. The solution is to replace
>>>>> unsigned int with another 64-bit type, such as erofs_off_t.
>>>>>        cur = end - min_t(unsigned int, offset + end - map->m_la, end);
>>>>>        - For example:
>>>>>            - offset = 0x400160000
>>>>>            - end = 0x370
>>>>>            - map->m_la = 0x160370
>>>>>            - offset + end - map->m_la = 0x400000000
>>>>>            - offset + end - map->m_la = 0x00000000 (truncated as unsigned int)
>>>>
>>>> Thanks for the catch!
>>>>
>>>> Could you split these two into two patches?
>>>>
>>>> how about using:
>>>> cur = end - min_t(erofs_off_t, offend + end - map->m_la, end)
>>>> for this?
>>>>
>>>> since cur and end are all [0, PAGE_SIZE - 1] for now, and
>>>> folio_size() later.
>>>
>>> OK. I will split the patch.
>>>
>>> Sorry that I can not understand what is 'offend' refer to and what do you mean. Could you please describe it more clearly?
>>
>> Sorry, there is a typo here, I meant 'offset'.
>>
>> `cur` and `end` both are not exceed 4096 if your page_size
>> is 4096.
>>
>> Does
>> cur = end - min_t(erofs_off_t, offset + end - map->m_la, end)
>>
>> fix your issue?
> 
> Yes. I think this will fix this issue. Do you mean the below change is unncessary?
>  >>>> -    unsigned int cur, end, spiltted;
>  >>>> +    erofs_off_t cur, end;
>  >>>> +    unsigned int spiltted;

Yes, please help send a fix for this!

Thanks,
Gao Xiang

On 2023/7/10 13:02, Gao Xiang wrote:
> 
> 
> On 2023/7/10 12:35, Chunhai Guo wrote:
>>
>>
>> On 2023/7/10 11:37, Gao Xiang wrote:
>>>
>>>
>>> On 2023/7/10 11:32, Chunhai Guo wrote:
>>>> Hi Xiang,
>>>>
>>>> On 2023/7/8 17:00, Gao Xiang wrote:
>>>>> Hi Chunhai,
>>>>>
>>>>> On 2023/7/8 14:24, Chunhai Guo wrote:
>>>>>> When z_erofs_read_folio() reads a page with an offset far beyond EOF, two
>>>>>> issues may occur:
>>>>>> - z_erofs_pcluster_readmore() may take a long time to loop when the offset
>>>>>>       is big enough, which is unnecessary.
>>>>>>         - For example, it will loop 4691368 times and take about 27 seconds
>>>>>>           with following case.
>>>>>>             - offset = 19217289215
>>>>>>             - inode_size = 1442672
>>>>>> - z_erofs_do_read_page() may loop infinitely due to the inappropriate
>>>>>>       truncation in the below statement. Since the offset is 64 bits and
>>>>>> min_t() truncates the result to 32 bits. The solution is to replace
>>>>>> unsigned int with another 64-bit type, such as erofs_off_t.
>>>>>>         cur = end - min_t(unsigned int, offset + end - map->m_la, end);
>>>>>>         - For example:
>>>>>>             - offset = 0x400160000
>>>>>>             - end = 0x370
>>>>>>             - map->m_la = 0x160370
>>>>>>             - offset + end - map->m_la = 0x400000000
>>>>>>             - offset + end - map->m_la = 0x00000000 (truncated as unsigned int)
>>>>>
>>>>> Thanks for the catch!
>>>>>
>>>>> Could you split these two into two patches?
>>>>>
>>>>> how about using:
>>>>> cur = end - min_t(erofs_off_t, offend + end - map->m_la, end)
>>>>> for this?
>>>>>
>>>>> since cur and end are all [0, PAGE_SIZE - 1] for now, and
>>>>> folio_size() later.
>>>>
>>>> OK. I will split the patch.
>>>>
>>>> Sorry that I can not understand what is 'offend' refer to and what do you mean. Could you please describe it more clearly?
>>>
>>> Sorry, there is a typo here, I meant 'offset'.
>>>
>>> `cur` and `end` both are not exceed 4096 if your page_size
>>> is 4096.
>>>
>>> Does
>>> cur = end - min_t(erofs_off_t, offset + end - map->m_la, end)
>>>
>>> fix your issue?
>>
>> Yes. I think this will fix this issue. Do you mean the below change is unncessary?
>>   >>>> -    unsigned int cur, end, spiltted;
>>   >>>> +    erofs_off_t cur, end;
>>   >>>> +    unsigned int spiltted;
> 
> Yes, please help send a fix for this!
> 
> Thanks,
> Gao Xiang
> 

Got it. I have sent the patch. Please have a check.

Thanks,
Guo Chunhai