drivers.
The bug occurrs when a userland process has the driver instance
open and the underlying device goes away. We get the devfs
callback that the device node has been destroyed, but not all of
the closes necessary to fully decrement the reference count on the
CAM peripheral.
The reason is that once devfs calls back and says the device has
been destroyed, it is moved off to deadfs, and devfs guarantees
that there will be no more open or close calls. So the solution
is to keep track of how many outstanding open calls there are on
the device, and just release that many references when we get the
callback from devfs.
scsi_pass.c,
scsi_enc.c,
scsi_enc_internal.h: Add an open count to the softc in these
drivers. Increment it on open and
decrement it on close.
When we get a devfs callback to say that
the device node has gone away, decrement
the peripheral reference count by the
number of still outstanding opens.
Make sure we don't access the peripheral
with cam_periph_unlock() after what might
be the final call to
cam_periph_release_locked(). The
peripheral might have been freed, and we
will be dereferencing freed memory.
scsi_ch.c,
scsi_sg.c: For the ch(4) and sg(4) drivers, add the
same changes described above, and in
addition, fix another bug that was
previously fixed in the pass(4) and enc(4)
drivers.
These drivers were calling destroy_dev()
from their cleanup routine, but that could
cause a deadlock because the cleanup
routine could be indirectly called from
the driver's close routine. This would
cause a deadlock, because the device node
is being held open by the active close
call, and can't be destroyed.
Sponsored by: Spectra Logic Corporation
MFC after: 1 week
of this hardware still running (close to twenty years now).
2. Quiesece and use ENC_VLOG instead of ENC_LOG for most
complaints. That is, they're visible with bootverbose, but
otherwise quiesced and not repeatedly spamming messages
with constant reminders that hardware in this space is
rarely fully compliant.
MFC after: 1 month
'encapsulating interface' used with IPsec and has nothing to do with
storage 'enclosure' services.
MFC after: 3 days
Noticed while: debugging why enc(4) is no longer automatically created
the pass(4) and enc(4) drivers and devfs.
The pass(4) driver uses the destroy_dev_sched() routine to
schedule its device node for destruction in a separate thread
context. It does this because the passcleanup() routine can get
called indirectly from the passclose() routine, and that would
cause a deadlock if the close routine tried to destroy its own
device node.
In any case, once a particular passthrough driver number, e.g.
pass3, is destroyed, CAM considers that unit number (3 in this
case) available for reuse.
The problem is that devfs may not be done cleaning up the previous
instance of pass3, and will panic if isn't done cleaning up the
previous instance.
The solution is to get a callback from devfs when the device node
is removed, and make sure we hold a reference to the peripheral
until that happens.
Testing exposed some other cases where we have reference counting
issues, and those were also fixed in the pass(4) driver.
cam_periph.c: In camperiphfree(), reorder some of the operations.
The peripheral destructor needs to be called before
the peripheral is removed from the peripheral is
removed from the list. This is because once we
remove the peripheral from the list, and drop the
topology lock, the peripheral number may be reused.
But if the destructor hasn't been called yet, there
may still be resources hanging around (like devfs
nodes) that haven't been fully cleaned up.
cam_xpt.c: Add an argument to xpt_remove_periph() to indicate
whether the topology lock is already held.
scsi_enc.c: Acquire an extra reference to the peripheral during
registration, and release it once we get a callback
from devfs indicating that the device node is gone.
Call destroy_dev_sched_cb() in enc_oninvalidate()
instead of calling destroy_dev() in the cleanup
routine.
scsi_pass.c: Add reference counting to handle peripheral and
devfs object lifetime issues.
Add a reference to the peripheral and the devfs
node in the peripheral registration.
Don't attempt to add a physical path alias if the
peripheral has been marked invalid.
Release the devfs reference once the initial
physical path alias taskqueue run has completed.
Schedule devfs node destruction in the
passoninvalidate(), and release our peripheral
reference in a new routine, passdevgonecb() once
the devfs node is gone. This allows the peripheral
to fully go away, and the peripheral destructor,
passcleanup(), will get called.
MFC after: 3 days
Sponsored by: Spectra Logic
are handled in most CAM peripheral drivers that are not handled by
GEOM's disk class.
The usual character driver open and close semantics are that the
driver gets N open calls, but only one close, when the last caller
closes the device.
CAM peripheral drivers expect that behavior to be honored to the
letter, and the CAM peripheral driver code (specifically
cam_periph_release_locked_busses()) panics if it is done incorrectly.
Since devfs has to drop its locks while it calls a driver's close
routine, and it does not have a way to delay or prevent open calls
while it is calling the close routine, there is a race.
The sequence of events, simplified a bit, is:
- devfs acquires a lock
- devfs checks the reference count, and if it is 1, continues to close.
- devfs releases the lock
- 2nd process open call on the device happens here
- devfs calls the driver's close routine
- devfs acquires a lock
- devfs decrements the reference count
- devfs releases the lock
- 2nd process close call on the device happens here
At the second close, we get a panic in
cam_periph_release_locked_busses(), complaining that peripheral
has been released when the reference count is already 0. This is
because we have gotten two closes in a row, which should not
happen.
The fix is to add the D_TRACKCLOSE flag to the driver's cdevsw, so
that we get a close() call for each open(). That does happen
reliably, so we can make sure that our reference counts are
correct.
Note that the sa(4) and pt(4) drivers only allow one context
through the open routine. So these drivers aren't exposed to the
same race condition.
scsi_ch.c,
scsi_enc.c,
scsi_enc_internal.h,
scsi_pass.c,
scsi_sg.c:
For these drivers, change the open() routine to
increment the reference count for every open, and
just decrement the reference count in the close.
Call cam_periph_release_locked() in some scenarios
to avoid additional lock and unlock calls.
scsi_pt.c: Call cam_periph_release_locked() in some scenarios
to avoid additional lock and unlock calls.
MFC after: 3 days
process exit. Instead use CAM's standard reference counting to prevent
periph going away until process won't complete. I think that sleep in
single CAM SWI thread is not a good idea and may lead to deadlocks if
daemon process waits for some command completion. Combined with recent
patch avoiding use of CAM SWI for ATA it just causes panics because of
sleeps prohibited in interrupt thread context.
Revamp the CAM enclosure services driver.
This updated driver uses an in-kernel daemon to track state changes and
publishes physical path location information\for disk elements into the
CAM device database.
Sponsored by: Spectra Logic Corporation
Sponsored by: iXsystems, Inc.
Submitted by: gibbs, will, mav
