Messages in this thread |  | | Date | Thu, 15 Aug 2002 21:39:29 +0900 (JST) | Subject | 2.4.18(19) swapcache oops | From | j-nomura@ce ... |
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Hello,
I'm using 2.4.18 kernel and suspect there are swapcache race. I looked into 2.4.19 patch but could not find the fix to it.
The race condition is described below. Do you have any idea?
In the situation such as: - two processes (process A and B) sharing memory space - one of the pages in the space has been swapped out and not remained in swapcache - process A runs on cpu0, process B runs on cpu1
when process A reads the address corresponding to the page, page fault occurs and the cpu0 reads swapped-out page into memory, calls add_to_page_cache_unique() to add it to swapcache and then calls lru_cache_add() to add it to lru list.
If process B reads the same address at that time, cpu1 calls do_swap_page() and lookup_swap_cache() may succeed before cpu0 calls lru_cache_add() and cpu1 will set the page active by following mark_page_accessed().
lru_cache_add() checks if the page is active and if it is active, it calls BUG().
process A process B cpu0 cpu1 ----------------------------------------------------------- do_swap_page() spinunlock(mm->page_table_lock) spinlock(mm->page_table_lock) lookup_swap_cache() read_swap_cache_async() alloc_page() add_to_swap_cache_unique() __add_to_page_cache() do_swap_page() lookup_swap_cache() mark_page_accessed() lru_cache_add()
Best regards. -- NOMURA, Jun'ichi <j-nomura@ce.jp.nec.com, nomura@hpc.bs1.fc.nec.co.jp> HPC Operating System Group, 1st Computers Software Division, Computers Software Operations Unit, NEC Solutions. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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