[PATCH] floppy: force media-change checks when clearing events

[Cen Zhang]

floppy_open() tries to make blocking read/write opens perform a fresh
media-change check by clearing drive_state[drive].last_checked before
calling disk_check_media_change().  That timestamp is also updated by
disk_change() when another FDC operation observes that the disk-change
line is clear.

The worker path that calls disk_change() is not serialized by the
floppy_mutex/open_lock pair held by floppy_open().  A worker can therefore
store a recent jiffies value after floppy_open() stores zero and before the
synchronous disk_check_media_change() call reaches floppy_check_events().
The checkfreq throttle can then treat the media-change state as fresh and
skip the hardware poll that the open path explicitly tried to force.

Use the block layer's clearing mask instead of a racy timestamp sentinel.
When DISK_EVENT_MEDIA_CHANGE is being synchronously cleared, bypass the
checkfreq throttle and poll the drive.  Periodic event checks still use
last_checked to avoid unnecessary polling, and floppy_open() no longer
needs to write last_checked itself.

Signed-off-by: Cen Zhang <zzzccc427@xxxxxxxxx>
---
 drivers/block/floppy.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index 92e446a643712..7217db0b907b3 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -4051,7 +4051,6 @@ static int floppy_open(struct gendisk *disk, blk_mode_t mode)
 		fdc_state[FDC(drive)].rawcmd = 2;
 	if (!(mode & BLK_OPEN_NDELAY)) {
 		if (mode & (BLK_OPEN_READ | BLK_OPEN_WRITE)) {
-			drive_state[drive].last_checked = 0;
 			clear_bit(FD_OPEN_SHOULD_FAIL_BIT,
 				  &drive_state[drive].flags);
 			if (disk_check_media_change(disk))
@@ -4092,7 +4091,9 @@ static unsigned int floppy_check_events(struct gendisk *disk,
 	    test_bit(FD_VERIFY_BIT, &drive_state[drive].flags))
 		return DISK_EVENT_MEDIA_CHANGE;
 
-	if (time_after(jiffies, drive_state[drive].last_checked + drive_params[drive].checkfreq)) {
+	if ((clearing & DISK_EVENT_MEDIA_CHANGE) ||
+	    time_after(jiffies, drive_state[drive].last_checked +
+			       drive_params[drive].checkfreq)) {
 		if (lock_fdc(drive))
 			return 0;
 		poll_drive(false, 0);
-- 
2.43.0