ee37d7314a
[Symptom]
Resync thread hang when new added disk faulty during replacing.
[Root Cause]
In raid10_sync_request(), we expect to issue a bio with callback
end_sync_read(), and a bio with callback end_sync_write().
In normal situation, we will add resyncing sectors into
mddev->recovery_active when raid10_sync_request() returned, and sub
resynced sectors from mddev->recovery_active when end_sync_write()
calls end_sync_request().
If new added disk, which are replacing the old disk, is set faulty,
there is a race condition:
1. In the first rcu protected section, resync thread did not detect
that mreplace is set faulty and pass the condition.
2. In the second rcu protected section, mreplace is set faulty.
3. But, resync thread will prepare the read object first, and then
check the write condition.
4. It will find that mreplace is set faulty and do not have to
prepare write object.
This cause we add resync sectors but never sub it.
[How to Reproduce]
This issue can be easily reproduced by the following steps:
mdadm -C /dev/md0 --assume-clean -l 10 -n 4 /dev/sd[abcd]
mdadm /dev/md0 -a /dev/sde
mdadm /dev/md0 --replace /dev/sdd
sleep 1
mdadm /dev/md0 -f /dev/sde
[How to Fix]
This issue can be fixed by using local variables to record the result
of test conditions. Once the conditions are satisfied, we can make sure
that we need to issue a bio for read and a bio for write.
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README
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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.