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Fix a race between daopen and damediapoll

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When we do a daopen, we call dareprobe and wait for the results. The repoll runs
the da state machine up through the DA_STATE_RC* and then exits.

For removable media, we poll the device every 3 seconds with a TUR to see if it
has disappeared. This introduces a race. If the removable device has lots of
partitions, and if it's a little slow (like say a USB2 connected USB stick),
then we can have a fair amount of time that this reporbe is going on for. If,
during that time, damediapoll fires, it calls daschedule which changes the
scheduling priority from NONE to NORMAL. When that happens, the careful single
stepping in the da state machine is disrupted and we wind up sceduling multiple
read capacity calls. The first one succeeds and releases the reference. The
second one succeeds and releases the reference (and panics if the right code is
compiled into the da driver).

To avoid the race, only do the TUR calls while in state normal, otherwise just
reschedule damediapoll. This prevents the race from happening.
This commit is contained in:
Warner Losh 2019-11-13 01:58:43 +00:00
parent a1b2b6e184
commit 02fa548cde
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=354668
1 changed files with 1 additions and 0 deletions
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sys/cam/scsi/scsi_da.c
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@ -5949,6 +5949,7 @@ damediapoll(void *arg)
if (!cam_iosched_has_work_flags(softc->cam_iosched, DA_WORK_TUR) &&
(softc->flags & DA_FLAG_TUR_PENDING) == 0 &&
softc->state == DA_STATE_NORMAL &&
LIST_EMPTY(&softc->pending_ccbs)) {
if (da_periph_acquire(periph, DA_REF_TUR) == 0) {
cam_iosched_set_work_flags(softc->cam_iosched, DA_WORK_TUR);