drbd: fix potential deadlock on detach
If we have contention in drbd_al_begin_iod (heavy randon IO),
an administrative request to detach the disk may deadlock
for similar reasons as the recently fixed deadlock if detaching
because of IO-error.
The approach taken here is to either go through the intermediate
cleanup state D_FAILED, or first lock out application io,
don't just go directly to D_DISKLESS.
We need an additional state bit (WAS_IO_ERROR) to distinguish
the -> D_FAILED because of IO-error from other failures.
Sanitize D_ATTACHING -> D_FAILED to D_ATTACHING -> D_DISKLESS.
If only attaching, ldev may be missing still, but would be referenced
from within the after_state_ch for -> D_FAILED, potentially
dereferencing a NULL pointer.
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index e0e0bf6..03c15e3 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -852,7 +852,8 @@
BITMAP_IO, /* suspend application io;
once no more io in flight, start bitmap io */
BITMAP_IO_QUEUED, /* Started bitmap IO */
- GO_DISKLESS, /* Disk failed, local_cnt reached zero, we are going diskless */
+ GO_DISKLESS, /* Disk is being detached, on io-error or admin request. */
+ WAS_IO_ERROR, /* Local disk failed returned IO error */
RESYNC_AFTER_NEG, /* Resync after online grow after the attach&negotiate finished. */
NET_CONGESTED, /* The data socket is congested */
@@ -1281,6 +1282,7 @@
extern int drbd_bmio_clear_n_write(struct drbd_conf *mdev);
extern int drbd_bitmap_io(struct drbd_conf *mdev, int (*io_fn)(struct drbd_conf *), char *why);
extern void drbd_go_diskless(struct drbd_conf *mdev);
+extern void drbd_ldev_destroy(struct drbd_conf *mdev);
/* Meta data layout
@@ -1798,17 +1800,17 @@
case EP_PASS_ON:
if (!forcedetach) {
if (__ratelimit(&drbd_ratelimit_state))
- dev_err(DEV, "Local IO failed in %s."
- "Passing error on...\n", where);
+ dev_err(DEV, "Local IO failed in %s.\n", where);
break;
}
/* NOTE fall through to detach case if forcedetach set */
case EP_DETACH:
case EP_CALL_HELPER:
+ set_bit(WAS_IO_ERROR, &mdev->flags);
if (mdev->state.disk > D_FAILED) {
_drbd_set_state(_NS(mdev, disk, D_FAILED), CS_HARD, NULL);
- dev_err(DEV, "Local IO failed in %s."
- "Detaching...\n", where);
+ dev_err(DEV,
+ "Local IO failed in %s. Detaching...\n", where);
}
break;
}
@@ -2127,7 +2129,11 @@
__release(local);
D_ASSERT(i >= 0);
if (i == 0) {
+ if (mdev->state.disk == D_DISKLESS)
+ /* even internal references gone, safe to destroy */
+ drbd_ldev_destroy(mdev);
if (mdev->state.disk == D_FAILED)
+ /* all application IO references gone. */
drbd_go_diskless(mdev);
wake_up(&mdev->misc_wait);
}
@@ -2138,6 +2144,10 @@
{
int io_allowed;
+ /* never get a reference while D_DISKLESS */
+ if (mdev->state.disk == D_DISKLESS)
+ return 0;
+
atomic_inc(&mdev->local_cnt);
io_allowed = (mdev->state.disk >= mins);
if (!io_allowed)
