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Resizing currently drops consumer lock. This can cause entries to be
reordered, which isn't good in itself. More importantly, consumer can
detect a false ring empty condition and block forever.
Further, nesting of consumer within producer lock is problematic for
tun, since it produces entries in a BH, which causes a lock order
reversal:
CPU0 CPU1
---- ----
consume:
lock(&(&r->consumer_lock)->rlock);
resize:
local_irq_disable();
lock(&(&r->producer_lock)->rlock);
lock(&(&r->consumer_lock)->rlock);
<Interrupt>
produce:
lock(&(&r->producer_lock)->rlock);
To fix, nest producer lock within consumer lock during resize,
and keep consumer lock during the whole swap operation.
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: stable@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. 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.