From: Hugh Dickins <hugh@veritas.com>
2.6.3-mm UP without PREEMPT easily hangs looping around pdflush's
sync_sb_inodes, failing the down_read_trylock in do_writepages, but giving
the concurrent sync no chance to complete: just try while : ; do echo
$SECONDS; sync; cp /etc/termcap .; done
---
mm/page-writeback.c | 28 ++++++++++++----------------
1 files changed, 12 insertions(+), 16 deletions(-)
diff -puN mm/page-writeback.c~O_DIRECT-vs-buffered-fix-pdflush-hang-fix mm/page-writeback.c
--- 25/mm/page-writeback.c~O_DIRECT-vs-buffered-fix-pdflush-hang-fix 2004-02-24 12:19:55.000000000 -0800
+++ 25-akpm/mm/page-writeback.c 2004-02-24 12:19:55.000000000 -0800
@@ -483,30 +483,26 @@ void __init page_writeback_init(void)
int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
{
int ret;
- if (wbc->sync_mode == WB_SYNC_NONE) {
- if (!down_read_trylock(&mapping->wb_rwsema))
- /*
- * SYNC writeback in progress
- */
- return 0;
- } else {
- /*
- * Only allow 1 SYNC writeback at a time, to be able
- * to wait for all i/o without worrying about racing
- * WB_SYNC_NONE writers.
- */
+
+ /*
+ * Only allow 1 SYNC writeback at a time, to be able to wait for all
+ * I/O without worrying about racing WB_SYNC_NONE writers.
+ */
+ if (wbc->sync_mode == WB_SYNC_NONE)
+ down_read(&mapping->wb_rwsema);
+ else
down_write(&mapping->wb_rwsema);
- }
if (mapping->a_ops->writepages)
ret = mapping->a_ops->writepages(mapping, wbc);
else
ret = generic_writepages(mapping, wbc);
- if (wbc->sync_mode == WB_SYNC_NONE) {
+
+ if (wbc->sync_mode == WB_SYNC_NONE)
up_read(&mapping->wb_rwsema);
- } else {
+ else
up_write(&mapping->wb_rwsema);
- }
+
return ret;
}
_