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srcu: Remove cleanup_srcu_struct_quiesced()

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The cleanup_srcu_struct_quiesced() function was added because NVME
used WQ_MEM_RECLAIM workqueues and SRCU did not, which meant that
NVME workqueues waiting on SRCU workqueues could result in deadlocks
during low-memory conditions.  However, SRCU now also has WQ_MEM_RECLAIM
workqueues, so there is no longer a potential for deadlock.  Furthermore,
it turns out to be extremely hard to use cleanup_srcu_struct_quiesced()
correctly due to the fact that SRCU callback invocation accesses the
srcu_struct structure's per-CPU data area just after callbacks are
invoked.  Therefore, the usual practice of using srcu_barrier() to wait
for callbacks to be invoked before invoking cleanup_srcu_struct_quiesced()
fails because SRCU's callback-invocation workqueue handler might be
delayed, which can result in cleanup_srcu_struct_quiesced() being invoked
(and thus freeing the per-CPU data) before the SRCU's callback-invocation
workqueue handler is finished using that per-CPU data.  Nor is this a
theoretical problem: KASAN emitted use-after-free warnings because of
this problem on actual runs.

In short, NVME can now safely invoke cleanup_srcu_struct(), which
avoids the use-after-free scenario.  And cleanup_srcu_struct_quiesced()
is quite difficult to use safely.  This commit therefore removes
cleanup_srcu_struct_quiesced(), switching its sole user back to
cleanup_srcu_struct().  This effectively reverts the following pair
of commits:

f7194ac32c ("srcu: Add cleanup_srcu_struct_quiesced()")
4317228ad9 ("nvme: Avoid flush dependency in delete controller flow")

Reported-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Bart Van Assche <bvanassche@acm.org>
This commit is contained in:
Paul E. McKenney 2019-02-13 13:54:37 -08:00
parent 5cdfd174ea
commit f5ad399149
5 changed files with 18 additions and 66 deletions
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30
kernel/rcu/srcutree.c
View file

@ -360,8 +360,14 @@ static unsigned long srcu_get_delay(struct srcu_struct *ssp)
return SRCU_INTERVAL;
}
/* Helper for cleanup_srcu_struct() and cleanup_srcu_struct_quiesced(). */
void _cleanup_srcu_struct(struct srcu_struct *ssp, bool quiesced)
/**
* cleanup_srcu_struct - deconstruct a sleep-RCU structure
* @ssp: structure to clean up.
*
* Must invoke this after you are finished using a given srcu_struct that
* was initialized via init_srcu_struct(), else you leak memory.
*/
void cleanup_srcu_struct(struct srcu_struct *ssp)
{
int cpu;
@ -369,24 +375,12 @@ void _cleanup_srcu_struct(struct srcu_struct *ssp, bool quiesced)
return; /* Just leak it! */
if (WARN_ON(srcu_readers_active(ssp)))
return; /* Just leak it! */
if (quiesced) {
if (WARN_ON(delayed_work_pending(&ssp->work)))
return; /* Just leak it! */
} else {
flush_delayed_work(&ssp->work);
}
flush_delayed_work(&ssp->work);
for_each_possible_cpu(cpu) {
struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu);
if (quiesced) {
if (WARN_ON(timer_pending(&sdp->delay_work)))
return; /* Just leak it! */
if (WARN_ON(work_pending(&sdp->work)))
return; /* Just leak it! */
} else {
del_timer_sync(&sdp->delay_work);
flush_work(&sdp->work);
}
del_timer_sync(&sdp->delay_work);
flush_work(&sdp->work);
if (WARN_ON(rcu_segcblist_n_cbs(&sdp->srcu_cblist)))
return; /* Forgot srcu_barrier(), so just leak it! */
}
@ -399,7 +393,7 @@ void _cleanup_srcu_struct(struct srcu_struct *ssp, bool quiesced)
free_percpu(ssp->sda);
ssp->sda = NULL;
}
EXPORT_SYMBOL_GPL(_cleanup_srcu_struct);
EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
/*
* Counts the new reader in the appropriate per-CPU element of the