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authorHugh Dickins <hughd@google.com>2012-11-16 23:15:04 +0100
committerLinus Torvalds <torvalds@linux-foundation.org>2012-11-16 23:33:04 +0100
commit0f3c42f522dc1ad7e27affc0a4aa8c790bce0a66 (patch)
treebfd85ce2e0fede607ad196258d8071c67897d9eb /mm/page_alloc.c
parenttmpfs: fix shmem_getpage_gfp() VM_BUG_ON (diff)
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tmpfs: change final i_blocks BUG to WARNING
Under a particular load on one machine, I have hit shmem_evict_inode()'s BUG_ON(inode->i_blocks), enough times to narrow it down to a particular race between swapout and eviction. It comes from the "if (freed > 0)" asymmetry in shmem_recalc_inode(), and the lack of coherent locking between mapping's nrpages and shmem's swapped count. There's a window in shmem_writepage(), between lowering nrpages in shmem_delete_from_page_cache() and then raising swapped count, when the freed count appears to be +1 when it should be 0, and then the asymmetry stops it from being corrected with -1 before hitting the BUG. One answer is coherent locking: using tree_lock throughout, without info->lock; reasonable, but the raw_spin_lock in percpu_counter_add() on used_blocks makes that messier than expected. Another answer may be a further effort to eliminate the weird shmem_recalc_inode() altogether, but previous attempts at that failed. So far undecided, but for now change the BUG_ON to WARN_ON: in usual circumstances it remains a useful consistency check. Signed-off-by: Hugh Dickins <hughd@google.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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