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This patch is intended to fix bug 825323 - FS turns read-only during a double
fault of a mirror leg and mirrored log's leg at the same time. It only
affects a 2-way mirror with a mirrored log. 3+-way mirrors and mirrors
without a mirrored log are not affected.
The problem resulted from the fact that the top level mirror was not
using 'noflush' when suspending before its "down-convert". When a
mirror image fails, the bios are queue until a suspend is recieved. If
it is a 'noflush' suspend, the bios can be safely requeued in the DM
core. If 'noflush' is not used, the bios must be pushed through the
target and if a device is failed for a mirror, that means issuing an
error. When an error is received by a file system, it results in it
turning read-only (depending on the FS).
Part of the problem was is due to the nature of the stacking involved in
using a mirror as a mirror's log. When an image in each fail, the top
level mirror stalls because it is waiting for a log flush. The other
stalls waiting for corrective action. When the repair command is issued,
the entire stacked arrangement is collapsed to a linear LV. The log
flush then fails (somewhat uncleanly) and the top-level mirror is suspended
without 'noflush' because it is a linear device.
This patch allows the log to be repaired first, which in turn allows the
top-level mirror's log flush to complete cleanly. The top-level mirror
is then secondarily reduced to a linear device - at which time this mirror
is suspended properly with 'noflush'.