mbox series

[v4,0/2] fix memory initialization deadlock

Message ID 20230908131737.1714750-1-artemyko@nvidia.com (mailing list archive)
Headers
Series fix memory initialization deadlock |

Message

Artemy Kovalyov Sept. 8, 2023, 1:17 p.m. UTC 
  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,
there are sequences of calls leading to rte_memseg_list_walk() which 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.

Artemy Kovalyov (2):
  eal: fix memory initialization deadlock
  eal: annotate rte_memseg_list_walk()

 lib/eal/common/eal_common_dynmem.c     | 5 ++++-
 lib/eal/common/eal_memalloc.h          | 3 ++-
 lib/eal/common/eal_private.h           | 3 ++-
 lib/eal/include/generic/rte_rwlock.h   | 4 ++++
 lib/eal/include/rte_lock_annotations.h | 5 +++++
 lib/eal/include/rte_memory.h           | 4 +++-
 lib/eal/linux/eal_memalloc.c           | 7 +++++--
 7 files changed, 25 insertions(+), 6 deletions(-)