On Tue, Aug 29, 2023 at 07:11PM +0200, andrey.konovalov@xxxxxxxxx wrote:
> From: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
>
> Add a reference counter for how many times a stack records has been added
> to stack depot.
>
> Do no yet decrement the refcount, this is implemented in one of the
> following patches.
>
> This is preparatory patch for implementing the eviction of stack records
> from the stack depot.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> ---
> lib/stackdepot.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index 5ad454367379..a84c0debbb9e 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -22,6 +22,7 @@
> #include <linux/mutex.h>
> #include <linux/percpu.h>
> #include <linux/printk.h>
> +#include <linux/refcount.h>
> #include <linux/slab.h>
> #include <linux/spinlock.h>
> #include <linux/stacktrace.h>
> @@ -60,6 +61,7 @@ struct stack_record {
> u32 hash; /* Hash in hash table */
> u32 size; /* Number of stored frames */
> union handle_parts handle;
> + refcount_t count;
> unsigned long entries[DEPOT_STACK_MAX_FRAMES]; /* Frames */
> };
>
> @@ -348,6 +350,7 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
> stack->hash = hash;
> stack->size = size;
> /* stack->handle is already filled in by depot_init_pool. */
> + refcount_set(&stack->count, 1);
> memcpy(stack->entries, entries, flex_array_size(stack, entries, size));
>
> /*
> @@ -452,6 +455,7 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
> /* Fast path: look the stack trace up without full locking. */
> found = find_stack(*bucket, entries, nr_entries, hash);
> if (found) {
> + refcount_inc(&found->count);
If someone doesn't use stack_depot_evict(), and the refcount eventually
overflows, it'll do a WARN (per refcount_warn_saturate()).
I think the interface needs to be different:
stack_depot_get(): increments refcount (could be inline if just
wrapper around refcount_inc())
stack_depot_put(): what stack_depot_evict() currently does
Then it's clear that if someone uses either stack_depot_get() or _put()
that these need to be balanced. Not using either will result in the old
behaviour of never evicting an entry.
> read_unlock_irqrestore(&pool_rwlock, flags);
> goto exit;
> }
> --
> 2.25.1
>
