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1b1b32f2c6
Intensive swapoff testing shows shmem_unuse spinning on an entry in shmem_swaplist pointing to itself: how does that come about? Days pass... First guess is this: shmem_delete_inode tests list_empty without taking the global mutex (so the swapping case doesn't slow down the common case); but there's an instant in shmem_unuse_inode's list_move_tail when the list entry may appear empty (a rare case, because it's actually moving the head not the the list member). So there's a danger of leaving the inode on the swaplist when it's freed, then reinitialized to point to itself when reused. Fix that by skipping the list_move_tail when it's a no-op, which happens to plug this. But this same spinning then surfaces on another machine. Ah, I'd never suspected it, but shmem_writepage's swaplist manipulation is unsafe: though we still hold page lock, which would hold off inode deletion if the page were in pagecache, it doesn't hold off once it's in swapcache (free_swap_and_cache doesn't wait on locked pages). Hmm: we could put the the inode on swaplist earlier, but then shmem_unuse_inode could never prune unswapped inodes. Fix this with an igrab before dropping info->lock, as in shmem_unuse_inode; though I am a little uneasy about the iput which has to follow - it works, and I see nothing wrong with it, but it is surprising that shmem inode deletion may now occur below shmem_writepage. Revisit this fix later? And while we're looking at these races: the way shmem_unuse tests swapped without holding info->lock looks unsafe, if we've more than one swap area: a racing shmem_writepage on another page of the same inode could be putting it in swapcache, just as we're deciding to remove the inode from swaplist - there's a danger of going on swap without being listed, so a later swapoff would hang, being unable to locate the entry. Move that test and removal down into shmem_unuse_inode, once info->lock is held. Signed-off-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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| .. | ||
| allocpercpu.c | ||
| backing-dev.c | ||
| bootmem.c | ||
| bounce.c | ||
| fadvise.c | ||
| filemap_xip.c | ||
| filemap.c | ||
| fremap.c | ||
| highmem.c | ||
| hugetlb.c | ||
| internal.h | ||
| Kconfig | ||
| madvise.c | ||
| Makefile | ||
| memory_hotplug.c | ||
| memory.c | ||
| mempolicy.c | ||
| mempool.c | ||
| migrate.c | ||
| mincore.c | ||
| mlock.c | ||
| mmap.c | ||
| mmzone.c | ||
| mprotect.c | ||
| mremap.c | ||
| msync.c | ||
| nommu.c | ||
| oom_kill.c | ||
| page_alloc.c | ||
| page_io.c | ||
| page_isolation.c | ||
| page-writeback.c | ||
| pdflush.c | ||
| prio_tree.c | ||
| quicklist.c | ||
| readahead.c | ||
| rmap.c | ||
| shmem_acl.c | ||
| shmem.c | ||
| slab.c | ||
| slob.c | ||
| slub.c | ||
| sparse-vmemmap.c | ||
| sparse.c | ||
| swap_state.c | ||
| swap.c | ||
| swapfile.c | ||
| thrash.c | ||
| tiny-shmem.c | ||
| truncate.c | ||
| util.c | ||
| vmalloc.c | ||
| vmscan.c | ||
| vmstat.c | ||