path: root/ipc
diff options
authorSebastian Andrzej Siewior <bigeasy@linutronix.de>2019-04-20 00:09:51 -0400
committerTheodore Ts'o <tytso@mit.edu>2019-04-20 00:09:56 -0400
commitb7d5dc21072cda7124d13eae2aefb7343ef94197 (patch)
tree09d1d9c39c919133652ffcc8509efbf7c3c2cb7d /ipc
parent92e507d216139b356a375afbda2824e85235e748 (diff)
random: add a spinlock_t to struct batched_entropy
The per-CPU variable batched_entropy_uXX is protected by get_cpu_var(). This is just a preempt_disable() which ensures that the variable is only from the local CPU. It does not protect against users on the same CPU from another context. It is possible that a preemptible context reads slot 0 and then an interrupt occurs and the same value is read again. The above scenario is confirmed by lockdep if we add a spinlock: | ================================ | WARNING: inconsistent lock state | 5.1.0-rc3+ #42 Not tainted | -------------------------------- | inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. | ksoftirqd/9/56 [HC0[0]:SC1[1]:HE0:SE0] takes: | (____ptrval____) (batched_entropy_u32.lock){+.?.}, at: get_random_u32+0x3e/0xe0 | {SOFTIRQ-ON-W} state was registered at: | _raw_spin_lock+0x2a/0x40 | get_random_u32+0x3e/0xe0 | new_slab+0x15c/0x7b0 | ___slab_alloc+0x492/0x620 | __slab_alloc.isra.73+0x53/0xa0 | kmem_cache_alloc_node+0xaf/0x2a0 | copy_process.part.41+0x1e1/0x2370 | _do_fork+0xdb/0x6d0 | kernel_thread+0x20/0x30 | kthreadd+0x1ba/0x220 | ret_from_fork+0x3a/0x50 … | other info that might help us debug this: | Possible unsafe locking scenario: | | CPU0 | ---- | lock(batched_entropy_u32.lock); | <Interrupt> | lock(batched_entropy_u32.lock); | | *** DEADLOCK *** | | stack backtrace: | Call Trace: … | kmem_cache_alloc_trace+0x20e/0x270 | ipmi_alloc_recv_msg+0x16/0x40 … | __do_softirq+0xec/0x48d | run_ksoftirqd+0x37/0x60 | smpboot_thread_fn+0x191/0x290 | kthread+0xfe/0x130 | ret_from_fork+0x3a/0x50 Add a spinlock_t to the batched_entropy data structure and acquire the lock while accessing it. Acquire the lock with disabled interrupts because this function may be used from interrupt context. Remove the batched_entropy_reset_lock lock. Now that we have a lock for the data scructure, we can access it from a remote CPU. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Diffstat (limited to 'ipc')
0 files changed, 0 insertions, 0 deletions

Privacy Policy