[PATCH] mtd: put flash block erasing into wait queue, if has any thread in queue

[Li Wang]

When erases many flash blocks, it maybe stop flash writing operation:
=====
erase thread:
for(;;) {
  do_erase_oneblock() {
    mutex_lock(&chip->mutex);
    chip->state = FL_ERASING;
    mutex_unlock(&chip->mutex);
    msleep();   <--- erase wait
    mutex_lock(&chip->mutex);
    chip->state = FL_READY;
    mutex_unlock(&chip->mutex);   <--- finish one block erasing
  }
}

write thread:
 retry:
  mutex_lock(&cfi->chips[chipnum].mutex);
  if (cfi->chips[chipnum].state != FL_READY) {
    set_current_state(TASK_UNINTERRUPTIBLE);
    add_wait_queue(&cfi->chips[chipnum].wq, &wait);
    mutex_unlock(&cfi->chips[chipnum].mutex);
    schedule();                   <--- write wait
    remove_wait_queue(&cfi->chips[chipnum].wq, &wait);
    goto retry;
=====
Only when finishes one block erasing, writing operation just has chance to run.
But, if writing operation is put into wait queue(write wait), the mutex_unlock
(finish one block erasing) can not wake up writing operation. So, if many blocks
need erase, writing operation has no chance to run.
it will cause the following backtrace:
=====
INFO: task sh:727 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
sh D 0fe76ad0 0 727 711 0x00000000
Call Trace:
[df0cdc40] [00000002] 0x2 (unreliable)
[df0cdd00] [c0008974] __switch_to+0x64/0xd8
[df0cdd10] [c043f2e4] schedule+0x218/0x408
[df0cdd60] [c04401f4] __mutex_lock_slowpath+0xd0/0x174
[df0cdda0] [c044087c] mutex_lock+0x5c/0x60
[df0cddc0] [c00ff18c] do_truncate+0x60/0xa8
[df0cde10] [c010d1d0] do_last+0x5a0/0x6d0
[df0cde40] [c010f778] do_filp_open+0x1d4/0x5e8
[df0cdf20] [c00fe0d0] do_sys_open+0x64/0x19c
[df0cdf40] [c0010d04] ret_from_syscall+0x0/0x4
--- Exception: c01 at 0xfe76ad0
    LR = 0xffd3ae8
...
sh D 0fe77068 0 607 590 0x00000000 
Call Trace: 
[dbca98e0] [c009ad4c] rcu_process_callbacks+0x38/0x4c (unreliable) 
[dbca99a0] [c0008974] __switch_to+0x64/0xd8 
[dbca99b0] [c043f2e4] schedule+0x218/0x408 
[dbca9a00] [c034bfa4] cfi_amdstd_write_words+0x364/0x480 
[dbca9a80] [c034c9b4] cfi_amdstd_write_buffers+0x8f4/0xca8 
[dbca9b10] [c03437ac] part_write+0xb0/0xe4 
[dbca9b20] [c02051f8] jffs2_flash_direct_writev+0xdc/0x140 
[dbca9b70] [c02079ac] jffs2_flash_writev+0x38c/0x4fc 
[dbca9bc0] [c01fc6ac] jffs2_write_dnode+0x140/0x5bc 
[dbca9c40] [c01fd0dc] jffs2_write_inode_range+0x288/0x514 
[dbca9cd0] [c01f5ed4] jffs2_write_end+0x190/0x37c 
[dbca9d10] [c00bf2f0] generic_file_buffered_write+0x100/0x26c 
[dbca9da0] [c00c1828] __generic_file_aio_write+0x2c0/0x4fc 
[dbca9e10] [c00c1ad4] generic_file_aio_write+0x70/0xf0 
[dbca9e40] [c0100398] do_sync_write+0xac/0x120 
[dbca9ee0] [c0101088] vfs_write+0xb4/0x184 
[dbca9f00] [c01012cc] sys_write+0x50/0x10c 
[dbca9f40] [c0010d04] ret_from_syscall+0x0/0x4 
--- Exception: c01 at 0xfe77068 
    LR = 0xffd3c8c
...
flash_erase R running 0 869 32566 0x00000000 
Call Trace: 
[dbc6dae0] [c0017ac0] kunmap_atomic+0x14/0x3c (unreliable) 
[dbc6dba0] [c0008974] __switch_to+0x64/0xd8 
[dbc6dbb0] [c043f2e4] schedule+0x218/0x408 
[dbc6dc00] [c043fbe4] schedule_timeout+0x170/0x2cc 
[dbc6dc50] [c00531f0] msleep+0x1c/0x34 
[dbc6dc60] [c034d538] do_erase_oneblock+0x7d0/0x944 
[dbc6dcd0] [c0349dfc] cfi_varsize_frob+0x1a8/0x2cc 
[dbc6dd20] [c034e4d4] cfi_amdstd_erase_varsize+0x30/0x60 
[dbc6dd30] [c0343abc] part_erase+0x80/0x104 
[dbc6dd40] [c0345c80] mtd_ioctl+0x3e0/0xc3c 
[dbc6de80] [c0111050] vfs_ioctl+0xcc/0xe4 
[dbc6dea0] [c011122c] do_vfs_ioctl+0x80/0x770 
[dbc6df10] [c01119b0] sys_ioctl+0x94/0x108 
[dbc6df40] [c0010d04] ret_from_syscall+0x0/0x4 
--- Exception: c01 at 0xff586a0 
    LR = 0xff58608 
=====
So, if there is any thread in wait queue, puts erasing operation into queue.
It makes writing operation have chance to run.

Signed-off-by: Li Wang <li.wang at windriver.com>
---
 drivers/mtd/chips/cfi_cmdset_0002.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c b/drivers/mtd/chips/cfi_cmdset_0002.c
index 5a4bfe3..53f5774 100644
--- a/drivers/mtd/chips/cfi_cmdset_0002.c
+++ b/drivers/mtd/chips/cfi_cmdset_0002.c
@@ -2400,6 +2400,19 @@ static int __xipram do_erase_oneblock(struct map_info *map, struct flchip *chip,
 	chip->state = FL_READY;
 	DISABLE_VPP(map);
 	put_chip(map, chip, adr);
+	if (waitqueue_active(&chip->wq)) {
+		set_current_state(TASK_UNINTERRUPTIBLE);
+		add_wait_queue(&chip->wq, &wait);
+		mutex_unlock(&chip->mutex);
+		/*
+		 * If the other thread in queue misses to wake up erasing in
+		 * 3ms, erasing will wake up itself. The way makes erasing not
+		 * to hang up by the error of the other thread in queue.
+		 */
+		schedule_timeout(msecs_to_jiffies(3));
+		remove_wait_queue(&chip->wq, &wait);
+		return ret;
+	}
 	mutex_unlock(&chip->mutex);
 	return ret;
 }
-- 
1.7.9.5