Messages in this thread | | | Date | Mon, 10 Jul 2023 17:37:28 +0800 | Subject | Re: [PATCH] erofs: fix two loop issues when read page beyond EOF | From | Chunhai Guo <> |
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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
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