4f7b6eef79
[ Upstream commit 3e16e83a62edac7617bfd8dbb4e55d04ff6adbe1 ]
Correct race condition where ioaccel is re-enabled before the raid_map is
updated. For RAID_1, RAID_1ADM, and RAID 5/6 there is a BUG_ON called which
is bad.
- Change event thread to disable ioaccel only. Send all requests down the
RAID path instead.
- Have rescan thread handle offload_enable.
- Since there is only one rescan allowed at a time, turning
offload_enabled on/off should not be racy. Each handler queues up a
rescan if one is already in progress.
- For timing diagram, offload_enabled is initially off due to a change
(transformation: splitmirror/remirror), ...
otbe = offload_to_be_enabled
oe = offload_enabled
Time Event Rescan Completion Request
Worker Worker Thread Thread
---- ------ ------ ---------- -------
T0 | | + UA |
T1 | + rescan started | 0x3f |
T2 + Event | | 0x0e |
T3 + Ack msg | | |
T4 | + if (!dev[i]->oe && | |
T5 | | dev[i]->otbe) | |
T6 | | get_raid_map | |
T7 + otbe = 1 | | |
T8 | | | |
T9 | + oe = otbe | |
T10 | | | + ioaccel request
T11 * BUG_ON
T0 - I/O completion with UA 0x3f 0x0e sets rescan flag.
T1 - rescan worker thread starts a rescan.
T2 - event comes in
T3 - event thread starts and issues "Acknowledge" message
...
T6 - rescan thread has bypassed code to reload new raid map.
...
T7 - event thread runs and sets offload_to_be_enabled
...
T9 - rescan thread turns on offload_enabled.
T10- request comes in and goes down ioaccel path.
T11- BUG_ON.
- After the patch is applied, ioaccel_enabled can only be re-enabled in
the re-scan thread.
Link: https://lore.kernel.org/r/158472877894.14200.7077843399036368335.stgit@brunhilda
Reviewed-by: Scott Teel <scott.teel@microsemi.com>
Reviewed-by: Matt Perricone <matt.perricone@microsemi.com>
Reviewed-by: Scott Benesh <scott.benesh@microsemi.com>
Signed-off-by: Don Brace <don.brace@microsemi.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.