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Subjectcorrection: fs/buffer.c underlocking async pages



Hi,

I ran into some problems with buffer.c trying to unlock a page of async io
buffer heads more
than once.
IMHO end_buffer_io_async() shouldn't rely on the value of b_end_io to
decide if the whole
page can be unlocked. It would make it easier for other layers (well
remappers like md or
lvm) to create an end_io chain without the need of allocating new buffer
heads just for that.
Is the comparision on b_end_io really necessary? I would assume that all
bh on the same
page belong to async io.
Otherwise, could something like below be done instead?

Linux for eServer development
Stefan.Bader@de.ibm.com
Phone: +49 (7031) 16-2472
----------------------------------------------------------------------------------
When all other means of communication fail, try words.

--------------------------------------------
diff -ruN old/fs/buffer.c new/fs/buffer.c
--- old/fs/buffer.c Thu Jun 21 09:47:20 2001
+++ new/fs/buffer.c Thu Jun 21 10:44:01 2001
@@ -798,11 +798,12 @@
* that unlock the page..
*/
spin_lock_irqsave(&page_uptodate_lock, flags);
+ clear_bit(BH_Async, &bh->b_state);
unlock_buffer(bh);
atomic_dec(&bh->b_count);
tmp = bh->b_this_page;
while (tmp != bh) {
- if (tmp->b_end_io == end_buffer_io_async &&
buffer_locked(tmp))
+ if (test_bit(BH_Async, &tmp->b_state) &&
buffer_locked(tmp))
goto still_busy;
tmp = tmp->b_this_page;
}
@@ -834,6 +835,7 @@

void set_buffer_async_io(struct buffer_head *bh) {
bh->b_end_io = end_buffer_io_async ;
+ set_bit(BH_Async, &bh->b_state);
}

/*
@@ -1535,6 +1537,7 @@
do {
lock_buffer(bh);
bh->b_end_io = end_buffer_io_async;
+ set_bit(BH_Async, &bh->b_state);
atomic_inc(&bh->b_count);
set_bit(BH_Uptodate, &bh->b_state);
clear_bit(BH_Dirty, &bh->b_state);
@@ -1736,6 +1739,7 @@
struct buffer_head * bh = arr[i];
lock_buffer(bh);
bh->b_end_io = end_buffer_io_async;
+ set_bit(BH_Async, &bh->b_state);
atomic_inc(&bh->b_count);
}

@@ -2182,6 +2186,7 @@
bh->b_blocknr = *(b++);
set_bit(BH_Mapped, &bh->b_state);
bh->b_end_io = end_buffer_io_async;
+ set_bit(BH_Async, &bh->b_state);
atomic_inc(&bh->b_count);
bh = bh->b_this_page;
} while (bh != head);
diff -ruN old/include/linux/fs.h new/include/linux/fs.h
--- old/include/linux/fs.h Thu Jun 21 09:47:51 2001
+++ new/include/linux/fs.h Thu Jun 21 09:48:20 2001
@@ -207,6 +207,7 @@
#define BH_Mapped 4 /* 1 if the buffer has a disk mapping */
#define BH_New 5 /* 1 if the buffer is new and not yet
written out */
#define BH_Protected 6 /* 1 if the buffer is protected */
+#define BH_Async 7 /* 1 if the buffer is used for asyncronous io */

/*
* Try to keep the most commonly used fields in single cache lines (16
-------------------


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