https://github.com/torvalds/linux
Revision e6780f7243eddb133cc20ec37fa69317c218b709 authored by Hugh Dickins on 31 December 2011, 19:44:01 UTC, committed by Linus Torvalds on 31 December 2011, 19:48:28 UTC
It was found (by Sasha) that if you use a futex located in the gate area we get stuck in an uninterruptible infinite loop, much like the ZERO_PAGE issue. While looking at this problem, PeterZ realized you'll get into similar trouble when hitting any install_special_pages() mapping. And are there still drivers setting up their own special mmaps without page->mapping, and without special VM or pte flags to make get_user_pages fail? In most cases, if page->mapping is NULL, we do not need to retry at all: Linus points out that even /proc/sys/vm/drop_caches poses no problem, because it ends up using remove_mapping(), which takes care not to interfere when the page reference count is raised. But there is still one case which does need a retry: if memory pressure called shmem_writepage in between get_user_pages_fast dropping page table lock and our acquiring page lock, then the page gets switched from filecache to swapcache (and ->mapping set to NULL) whatever the refcount. Fault it back in to get the page->mapping needed for key->shared.inode. Reported-by: Sasha Levin <levinsasha928@gmail.com> Signed-off-by: Hugh Dickins <hughd@google.com> Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Tip revision: e6780f7243eddb133cc20ec37fa69317c218b709 authored by Hugh Dickins on 31 December 2011, 19:44:01 UTC
futex: Fix uninterruptible loop due to gate_area
futex: Fix uninterruptible loop due to gate_area
Tip revision: e6780f7
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COPYING | -rw-r--r-- | 18.3 KB |
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