Re: [PATCH 5/9] lib/ref_tracker: improve allocation flags

Eric Dumazet
2022-02-17T15:13:32Z

On Thu, Feb 17, 2022 at 6:05 AM Andrzej Hajda <andrzej.hajda@intel.com> wrote:
>
> Library can be called in non-sleeping context, so it should not use
> __GFP_NOFAIL. Instead it should calmly handle allocation fails, for
> this __GFP_NOWARN has been added as well.

Your commit changelog is misleading .

The GFP_NOFAIL issue has been fixed already in
commit c12837d1bb31032bead9060dec99ef310d5b9fb7 ("ref_tracker: use
__GFP_NOFAIL more carefully")

>
> Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
> ---
> lib/ref_tracker.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/lib/ref_tracker.c b/lib/ref_tracker.c
> index 7b00bca300043..c8441ffbb058a 100644
> --- a/lib/ref_tracker.c
> +++ b/lib/ref_tracker.c
> @@ -59,7 +59,7 @@ __ref_tracker_dir_pr_ostream(struct ref_tracker_dir *dir,
> if (list_empty(&dir->list))
> return;
>
> - sbuf = kmalloc(STACK_BUF_SIZE, GFP_NOWAIT);
> + sbuf = kmalloc(STACK_BUF_SIZE, GFP_NOWAIT | __GFP_NOWARN);

This belongs to patch 3 in your series.

>
> list_for_each_entry(tracker, &dir->list, head)
> ++total;
> @@ -154,11 +154,11 @@ int ref_tracker_alloc(struct ref_tracker_dir *dir,
> unsigned long entries[REF_TRACKER_STACK_ENTRIES];
> struct ref_tracker *tracker;
> unsigned int nr_entries;
> - gfp_t gfp_mask = gfp;

Simply change this line to : gfp_t gfp_mask = gfp | __GFP_NOFAIL;

> + gfp_t gfp_mask;
> unsigned long flags;
>

Then leave all this code as is ? I find current code more readable.

> - if (gfp & __GFP_DIRECT_RECLAIM)
> - gfp_mask |= __GFP_NOFAIL;
> + gfp |= __GFP_NOWARN;
> + gfp_mask = (gfp & __GFP_DIRECT_RECLAIM) ? (gfp | __GFP_NOFAIL) : gfp;
> *trackerp = tracker = kzalloc(sizeof(*tracker), gfp_mask);
> if (unlikely(!tracker)) {
> pr_err_once("memory allocation failure, unreliable refcount tracker.\n");
> @@ -191,7 +191,8 @@ int ref_tracker_free(struct ref_tracker_dir *dir,
> }
> nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 1);
> nr_entries = filter_irq_stacks(entries, nr_entries);

lib/ref_tracker.c got patches in net-next, your patch series is going
to add conflicts.

git log --oneline 5740d0689096..4d449bdc5b26 --no-merges -- lib/ref_tracker.c
c2d1e3df4af59261777b39c2e47476acd4d1cbeb ref_tracker: remove
filter_irq_stacks() call
8fd5522f44dcd7f05454ddc4f16d0f821b676cd9 ref_tracker: add a count of
untracked references
e3ececfe668facd87d920b608349a32607060e66 ref_tracker: implement
use-after-free detection

> - stack_handle = stack_depot_save(entries, nr_entries, GFP_ATOMIC);
> + stack_handle = stack_depot_save(entries, nr_entries,
> + GFP_NOWAIT | __GFP_NOWARN);

This is fine.

>
> spin_lock_irqsave(&dir->lock, flags);
> if (tracker->dead) {
> --
> 2.25.1
>