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srcu: Prevent cleanup_srcu_struct() from freeing non-dynamic ->sda

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When an srcu_struct structure is created (but not in a kernel module)
by DEFINE_SRCU() and friends, the per-CPU srcu_data structure is
statically allocated.  In all other cases, that structure is obtained
from alloc_percpu(), in which case cleanup_srcu_struct() must invoke
free_percpu() on the resulting ->sda pointer in the srcu_struct pointer.

Which it does.

Except that it also invokes free_percpu() on the ->sda pointer
referencing the statically allocated per-CPU srcu_data structures.
Which free_percpu() is surprisingly OK with.

This commit nevertheless stops cleanup_srcu_struct() from freeing
statically allocated per-CPU srcu_data structures.

Co-developed-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney
2022-01-27 13:20:49 -08:00
parent 4a230f8046
commit 46470cf85d
2 changed files with 7 additions and 3 deletions
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1
include/linux/srcutree.h
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@@ -73,6 +73,7 @@ struct srcu_struct {
unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */
unsigned long srcu_last_gp_end; /* Last GP end timestamp (ns) */
struct srcu_data __percpu *sda; /* Per-CPU srcu_data array. */
bool sda_is_static; /* May ->sda be passed to free_percpu()? */
unsigned long srcu_barrier_seq; /* srcu_barrier seq #. */
struct mutex srcu_barrier_mutex; /* Serialize barrier ops. */
struct completion srcu_barrier_completion;