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>
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 658c4a7..cbd2ca99 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2439,6 +2439,7 @@
int no_nrwrite_index_update;
int pages_written = 0;
long pages_skipped;
+ int range_cyclic, cycled = 1, io_done = 0;
int needed_blocks, ret = 0, nr_to_writebump = 0;
struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);
@@ -2490,9 +2491,15 @@
if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
range_whole = 1;
- if (wbc->range_cyclic)
+ range_cyclic = wbc->range_cyclic;
+ if (wbc->range_cyclic) {
index = mapping->writeback_index;
- else
+ if (index)
+ cycled = 0;
+ wbc->range_start = index << PAGE_CACHE_SHIFT;
+ wbc->range_end = LLONG_MAX;
+ wbc->range_cyclic = 0;
+ } else
index = wbc->range_start >> PAGE_CACHE_SHIFT;
mpd.wbc = wbc;
@@ -2506,6 +2513,7 @@
wbc->no_nrwrite_index_update = 1;
pages_skipped = wbc->pages_skipped;
+retry:
while (!ret && wbc->nr_to_write > 0) {
/*
@@ -2548,6 +2556,7 @@
pages_written += mpd.pages_written;
wbc->pages_skipped = pages_skipped;
ret = 0;
+ io_done = 1;
} else if (wbc->nr_to_write)
/*
* There is no more writeout needed
@@ -2556,6 +2565,13 @@
*/
break;
}
+ if (!io_done && !cycled) {
+ cycled = 1;
+ index = 0;
+ wbc->range_start = index << PAGE_CACHE_SHIFT;
+ wbc->range_end = mapping->writeback_index - 1;
+ goto retry;
+ }
if (pages_skipped != wbc->pages_skipped)
printk(KERN_EMERG "This should not happen leaving %s "
"with nr_to_write = %ld ret = %d\n",
@@ -2563,6 +2579,7 @@
/* Update index */
index += pages_written;
+ wbc->range_cyclic = range_cyclic;
if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
/*
* set the writeback_index so that range_cyclic