Re: [PATCH v3] eal: fix memory initialization deadlock

[David Marchand <david.marchand@redhat.com>]

On Wed, Sep 6, 2023 at 11:53 AM Artemy Kovalyov <artemyko@nvidia.com> wrote:
>
> The issue arose due to the change in the DPDK read-write lock
> implementation. That change added a new flag, RTE_RWLOCK_WAIT, designed
> to prevent new read locks while a write lock is in the queue. However,
> this change has led to a scenario where a recursive read lock, where a
> lock is acquired twice by the same execution thread, can initiate a
> sequence of events resulting in a deadlock:
>
> Process 1 takes the first read lock.
> Process 2 attempts to take a write lock, triggering RTE_RWLOCK_WAIT due
> to the presence of a read lock. This makes process 2 enter a wait loop
> until the read lock is released.
> Process 1 tries to take a second read lock. However, since a write lock
> is waiting (due to RTE_RWLOCK_WAIT), it also enters a wait loop until
> the write lock is acquired and then released.
>
> Both processes end up in a blocked state, unable to proceed, resulting
> in a deadlock scenario.
>
> Following these changes, the RW-lock no longer supports
> recursion, implying that a single thread shouldn't obtain a read lock if
> it already possesses one. The problem arises during initialization: the
> rte_eal_init() function acquires the memory_hotplug_lock, and later on,
> the sequence of calls rte_eal_memory_init() -> eal_memalloc_init() ->
> rte_memseg_list_walk() acquires it again without releasing it. This
> scenario introduces the risk of a potential deadlock when concurrent
> write locks are applied to the same memory_hotplug_lock. To address this
> we resolved the issue by replacing rte_memseg_list_walk() with
> rte_memseg_list_walk_thread_unsafe().
>
> Implementing a lock annotation for rte_memseg_list_walk() to
> proactively identify bugs similar to this one during compile time.

The annotations are not necessary to the fix (that we will likely
backport in LTS versions).
Please split this change in two patches, to separate those annotations
from the fix.


>
> Bugzilla ID: 1277
> Fixes: 832cecc03d77 ("rwlock: prevent readers from starving writers")
> Cc: stable@dpdk.org
>
> Signed-off-by: Artemy Kovalyov <artemyko@nvidia.com>


-- 
David Marchand