Messages in this thread Patch in this message | | | Date | Wed, 15 Oct 2003 19:22:28 +0100 (BST) | From | Hugh Dickins <> | Subject | [PATCH] tmpfs 4/7 getpage/truncate race |
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Extend use of that SHMEM_PAGEIN flag to where shmem_getpage adds a page to the cache. It couldn't have caused a BUG_ON(inode->i_blocks), but if i_size is reduced (from another cpu) the instant after shmem_swp_alloc checks it, shmem_getpage could insert a page into the cache just after truncate_inode_pages has passed through cleaning it, leaving stale data (which may mysteriously reappear if the file is later extended).
Easily fixed for tmpfs, using the mechanism just added for swapoff; and probably more important there, since its read from swap can insert non-0 data. But is there not a similar issue, a tiny window, in filemap.c? if truncate_inode_pages comes in between checking i_size and adding new page to cache. Not worth getting excited, but something to beware of.
--- tmpfs3/mm/shmem.c 2003-10-15 15:38:52.342219504 +0100 +++ tmpfs4/mm/shmem.c 2003-10-15 15:39:03.328549328 +0100 @@ -52,7 +52,7 @@ #define VM_ACCT(size) (PAGE_CACHE_ALIGN(size) >> PAGE_SHIFT) -/* info->flags needs a VM_flag to handle swapoff/truncate races efficiently */ +/* info->flags needs a VM_flag to handle pagein/truncate races efficiently */ #define SHMEM_PAGEIN VM_READ /* Pretend that each entry is of this size in directory's i_size */ @@ -498,6 +498,8 @@ * Call truncate_inode_pages again: racing shmem_unuse_inode * may have swizzled a page in from swap since vmtruncate or * generic_delete_inode did it, before we lowered next_index. + * Also, though shmem_getpage checks i_size before adding to + * cache, no recheck after: so fix the narrow window there too. */ spin_unlock(&info->lock); truncate_inode_pages(inode->i_mapping, inode->i_size); @@ -863,6 +865,7 @@ swap_free(swap); } else if (!(error = move_from_swap_cache( swappage, idx, mapping))) { + info->flags |= SHMEM_PAGEIN; shmem_swp_set(info, entry, 0); shmem_swp_unmap(entry); spin_unlock(&info->lock); @@ -932,6 +935,7 @@ goto failed; goto repeat; } + info->flags |= SHMEM_PAGEIN; } info->alloced++; - 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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