Messages in this thread | | | Date | Mon, 10 Jul 2023 13:02:58 +0800 | Subject | Re: [PATCH] erofs: fix two loop issues when read page beyond EOF | From | Gao Xiang <> |
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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
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