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@ -982,7 +982,32 @@ xfs_vm_writepage( |
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offset = i_size_read(inode); |
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end_index = offset >> PAGE_CACHE_SHIFT; |
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last_index = (offset - 1) >> PAGE_CACHE_SHIFT; |
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if (page->index >= end_index) { |
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/*
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* The page index is less than the end_index, adjust the end_offset |
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* to the highest offset that this page should represent. |
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* ----------------------------------------------------- |
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* | file mapping | <EOF> | |
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* ----------------------------------------------------- |
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* | Page ... | Page N-2 | Page N-1 | Page N | | |
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* ^--------------------------------^----------|-------- |
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* | desired writeback range | see else | |
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* ---------------------------------^------------------| |
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*/ |
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if (page->index < end_index) |
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end_offset = (xfs_off_t)(page->index + 1) << PAGE_CACHE_SHIFT; |
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else { |
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/*
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* Check whether the page to write out is beyond or straddles |
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* i_size or not. |
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* ------------------------------------------------------- |
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* | file mapping | <EOF> | |
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* ------------------------------------------------------- |
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* | Page ... | Page N-2 | Page N-1 | Page N | Beyond | |
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* ^--------------------------------^-----------|--------- |
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* | | Straddles | |
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* ---------------------------------^-----------|--------| |
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*/ |
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unsigned offset_into_page = offset & (PAGE_CACHE_SIZE - 1); |
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/*
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@ -990,24 +1015,36 @@ xfs_vm_writepage( |
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* truncate operation that is in progress. We must redirty the |
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* page so that reclaim stops reclaiming it. Otherwise |
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* xfs_vm_releasepage() is called on it and gets confused. |
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* |
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* Note that the end_index is unsigned long, it would overflow |
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* if the given offset is greater than 16TB on 32-bit system |
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* and if we do check the page is fully outside i_size or not |
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* via "if (page->index >= end_index + 1)" as "end_index + 1" |
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* will be evaluated to 0. Hence this page will be redirtied |
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* and be written out repeatedly which would result in an |
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* infinite loop, the user program that perform this operation |
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* will hang. Instead, we can verify this situation by checking |
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* if the page to write is totally beyond the i_size or if it's |
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* offset is just equal to the EOF. |
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*/ |
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if (page->index >= end_index + 1 || offset_into_page == 0) |
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if (page->index > end_index || |
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(page->index == end_index && offset_into_page == 0)) |
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goto redirty; |
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/*
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* The page straddles i_size. It must be zeroed out on each |
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* and every writepage invocation because it may be mmapped. |
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* "A file is mapped in multiples of the page size. For a file |
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* that is not a multiple of the page size, the remaining |
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* that is not a multiple of the page size, the remaining |
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* memory is zeroed when mapped, and writes to that region are |
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* not written out to the file." |
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*/ |
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zero_user_segment(page, offset_into_page, PAGE_CACHE_SIZE); |
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/* Adjust the end_offset to the end of file */ |
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end_offset = offset; |
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} |
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end_offset = min_t(unsigned long long, |
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(xfs_off_t)(page->index + 1) << PAGE_CACHE_SHIFT, |
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offset); |
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len = 1 << inode->i_blkbits; |
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bh = head = page_buffers(page); |
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Dave Chinner
11 years ago