Messages in this thread | | | Date | Mon, 19 Sep 2005 21:14:10 +0100 (BST) | From | Hugh Dickins <> | Subject | Re: Multi-Threaded fork() correctness on Linux 2.4 & 2.6 |
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On Mon, 19 Sep 2005, Linus Torvalds wrote: > > We hold the page_table_lock when doing the fork(), so T2 can't actually be > copying the page until we've done the TLB flush, no? And once the TLB > flush is done, all the writes by T3 should be in the page, so we copy the > right thing at that point, and there is no consistency problems?
I was totally overlooking the page_table_lock during the fork.
But no matter, it's not good enough: src_mm->page_table_lock is acquired and dropped at the inner level, in copy_pte_range (looking at latest 2.6): it cannot be held across allocating page tables for dst_mm.
So each time T1 drops it, there's a window for the T2 vs. T3 problem. Yet we don't much want to flush TLB each time we leave copy_pte_range.
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