linux-kernel - Re: [PATCH v2] powerpc/qspinlock: Fix deadlock in MCS queue

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Message-Id: <172562323422.464302.13801524851924660182.b4-ty@ellerman.id.au>
Date: Fri, 06 Sep 2024 21:47:14 +1000
From: Michael Ellerman <patch-notifications@...erman.id.au>
To: Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>, "Nysal Jan K.A." <nysal@...ux.ibm.com>
Cc: stable@...r.kernel.org, Geetika Moolchandani <geetika@...ux.ibm.com>, Vaishnavi Bhat <vaish123@...ibm.com>, Jijo Varghese <vargjijo@...ibm.com>, Christophe Leroy <christophe.leroy@...roup.eu>, Naveen N Rao <naveen@...nel.org>, linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] powerpc/qspinlock: Fix deadlock in MCS queue

On Thu, 29 Aug 2024 07:58:27 +0530, Nysal Jan K.A. wrote:
> If an interrupt occurs in queued_spin_lock_slowpath() after we increment
> qnodesp->count and before node->lock is initialized, another CPU might
> see stale lock values in get_tail_qnode(). If the stale lock value happens
> to match the lock on that CPU, then we write to the "next" pointer of
> the wrong qnode. This causes a deadlock as the former CPU, once it becomes
> the head of the MCS queue, will spin indefinitely until it's "next" pointer
> is set by its successor in the queue.
> 
> [...]

Applied to powerpc/fixes.

[1/1] powerpc/qspinlock: Fix deadlock in MCS queue
      https://git.kernel.org/powerpc/c/734ad0af3609464f8f93e00b6c0de1e112f44559

cheers