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Commit06297d8cef("btrfs: switch extent_buffer blocking_writers from atomic to int") changed the type of blocking_writers but forgot to adjust relevant code in btrfs_tree_unlock by converting the smp_mb__after_atomic to smp_mb. This opened up the possibility of a deadlock due to re-ordering of setting blocking_writers and checking/waking up the waiter. This particular lockup is explained in a comment above waitqueue_active() function. Fix it by converting the memory barrier to a full smp_mb, accounting for the fact that blocking_writers is a simple integer. Fixes:06297d8cef("btrfs: switch extent_buffer blocking_writers from atomic to int") Tested-by: Johannes Thumshirn <jthumshirn@suse.com> Signed-off-by: Nikolay Borisov <nborisov@suse.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
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.