Messages in this thread | | | Date | Wed, 15 Sep 2004 14:29:20 +0200 | From | Andrea Arcangeli <> | Subject | truncate shows non zero data beyond the end of the inode with MAP_SHARED |
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Hello,
I've been told we're not posix compliant the way we handle MAP_SHARED on the last page of the inode. Basically after we map the page into userspace people can make the data beyond the i_size non-zero and we should clear it in the transition from page_mapcount 1 -> 0. The bug is that if you truncate-extend, the new data will not be guaranteed to be zero.
msync + power outage and writing to the page with sys_write at the same time it's being mapped (and in turn queueing it for pdflush writeout) are the two worst offeners. To fix those we'd need to mark the pte readonly, flush the tlb with a worst-case IPI broadcast, writepage, then mark the pte read-write and flush the tlb again with another IPI broadcast.
That is going to have a significant cost methinks. So maybe we shouldn't fix it after all... - 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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