ext4: Implement range_cyclic in ext4_da_writepages instead of write_cache_pages
With delayed allocation we lock the page in write_cache_pages() and try to build an in memory extent of contiguous blocks. This is needed so that we can get large contiguous blocks request. If range_cyclic mode is enabled, write_cache_pages() will loop back to the 0 index if no I/O has been done yet, and try to start writing from the beginning of the range. That causes an attempt to take the page lock of lower index page while holding the page lock of higher index page, which can cause a dead lock with another writeback thread. The solution is to implement the range_cyclic behavior in ext4_da_writepages() instead. http://bugzilla.kernel.org/show_bug.cgi?id=12579 Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
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@ -2439,6 +2439,7 @@ static int ext4_da_writepages(struct address_space *mapping,
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int no_nrwrite_index_update;
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int no_nrwrite_index_update;
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int pages_written = 0;
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int pages_written = 0;
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long pages_skipped;
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long pages_skipped;
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int range_cyclic, cycled = 1, io_done = 0;
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int needed_blocks, ret = 0, nr_to_writebump = 0;
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int needed_blocks, ret = 0, nr_to_writebump = 0;
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struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);
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struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);
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@ -2490,9 +2491,15 @@ static int ext4_da_writepages(struct address_space *mapping,
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if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
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if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
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range_whole = 1;
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range_whole = 1;
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if (wbc->range_cyclic)
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range_cyclic = wbc->range_cyclic;
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if (wbc->range_cyclic) {
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index = mapping->writeback_index;
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index = mapping->writeback_index;
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else
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if (index)
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cycled = 0;
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wbc->range_start = index << PAGE_CACHE_SHIFT;
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wbc->range_end = LLONG_MAX;
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wbc->range_cyclic = 0;
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} else
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index = wbc->range_start >> PAGE_CACHE_SHIFT;
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index = wbc->range_start >> PAGE_CACHE_SHIFT;
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mpd.wbc = wbc;
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mpd.wbc = wbc;
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@ -2506,6 +2513,7 @@ static int ext4_da_writepages(struct address_space *mapping,
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wbc->no_nrwrite_index_update = 1;
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wbc->no_nrwrite_index_update = 1;
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pages_skipped = wbc->pages_skipped;
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pages_skipped = wbc->pages_skipped;
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retry:
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while (!ret && wbc->nr_to_write > 0) {
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while (!ret && wbc->nr_to_write > 0) {
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/*
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/*
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@ -2548,6 +2556,7 @@ static int ext4_da_writepages(struct address_space *mapping,
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pages_written += mpd.pages_written;
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pages_written += mpd.pages_written;
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wbc->pages_skipped = pages_skipped;
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wbc->pages_skipped = pages_skipped;
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ret = 0;
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ret = 0;
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io_done = 1;
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} else if (wbc->nr_to_write)
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} else if (wbc->nr_to_write)
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/*
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/*
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* There is no more writeout needed
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* There is no more writeout needed
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@ -2556,6 +2565,13 @@ static int ext4_da_writepages(struct address_space *mapping,
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*/
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*/
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break;
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break;
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}
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}
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if (!io_done && !cycled) {
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cycled = 1;
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index = 0;
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wbc->range_start = index << PAGE_CACHE_SHIFT;
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wbc->range_end = mapping->writeback_index - 1;
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goto retry;
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}
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if (pages_skipped != wbc->pages_skipped)
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if (pages_skipped != wbc->pages_skipped)
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printk(KERN_EMERG "This should not happen leaving %s "
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printk(KERN_EMERG "This should not happen leaving %s "
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"with nr_to_write = %ld ret = %d\n",
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"with nr_to_write = %ld ret = %d\n",
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@ -2563,6 +2579,7 @@ static int ext4_da_writepages(struct address_space *mapping,
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/* Update index */
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/* Update index */
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index += pages_written;
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index += pages_written;
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wbc->range_cyclic = range_cyclic;
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if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
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if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
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/*
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/*
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* set the writeback_index so that range_cyclic
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* set the writeback_index so that range_cyclic
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