Re: [PATCH] lib/stackdepot: Double DEPOT_POOLS_CAP if KASAN is enabled

[Andrew Morton]

On Wed,  7 Aug 2024 12:52:28 -0400 Waiman Long <longman@xxxxxxxxxx> wrote:

> When a wide variety of workloads are run on a debug kernel with KASAN
> enabled, the following warning may sometimes be printed.
> 
>  [ 6818.650674] Stack depot reached limit capacity
>  [ 6818.650730] WARNING: CPU: 1 PID: 272741 at lib/stackdepot.c:252 depot_alloc_stack+0x39e/0x3d0
>    :
>  [ 6818.650907] Call Trace:
>  [ 6818.650909]  [<00047dd453d84b92>] depot_alloc_stack+0x3a2/0x3d0
>  [ 6818.650916]  [<00047dd453d85254>] stack_depot_save_flags+0x4f4/0x5c0
>  [ 6818.650920]  [<00047dd4535872c6>] kasan_save_stack+0x56/0x70
>  [ 6818.650924]  [<00047dd453587328>] kasan_save_track+0x28/0x40
>  [ 6818.650927]  [<00047dd45358a27a>] kasan_save_free_info+0x4a/0x70
>  [ 6818.650930]  [<00047dd45358766a>] __kasan_slab_free+0x12a/0x1d0
>  [ 6818.650933]  [<00047dd45350deb4>] kmem_cache_free+0x1b4/0x580
>  [ 6818.650938]  [<00047dd452c520da>] __put_task_struct+0x24a/0x320
>  [ 6818.650945]  [<00047dd452c6aee4>] delayed_put_task_struct+0x294/0x350
>  [ 6818.650949]  [<00047dd452e9066a>] rcu_do_batch+0x6ea/0x2090
>  [ 6818.650953]  [<00047dd452ea60f4>] rcu_core+0x474/0xa90
>  [ 6818.650956]  [<00047dd452c780c0>] handle_softirqs+0x3c0/0xf90
>  [ 6818.650960]  [<00047dd452c76fbe>] __irq_exit_rcu+0x35e/0x460
>  [ 6818.650963]  [<00047dd452c79992>] irq_exit_rcu+0x22/0xb0
>  [ 6818.650966]  [<00047dd454bd8128>] do_ext_irq+0xd8/0x120
>  [ 6818.650972]  [<00047dd454c0ddd0>] ext_int_handler+0xb8/0xe8
>  [ 6818.650979]  [<00047dd453589cf6>] kasan_check_range+0x236/0x2f0
>  [ 6818.650982]  [<00047dd453378cf0>] filemap_get_pages+0x190/0xaa0
>  [ 6818.650986]  [<00047dd453379940>] filemap_read+0x340/0xa70
>  [ 6818.650989]  [<00047dd3d325d226>] xfs_file_buffered_read+0x2c6/0x400 [xfs]
>  [ 6818.651431]  [<00047dd3d325dfe2>] xfs_file_read_iter+0x2c2/0x550 [xfs]
>  [ 6818.651663]  [<00047dd45364710c>] vfs_read+0x64c/0x8c0
>  [ 6818.651669]  [<00047dd453648ed8>] ksys_read+0x118/0x200
>  [ 6818.651672]  [<00047dd452b6cf5a>] do_syscall+0x27a/0x380
>  [ 6818.651676]  [<00047dd454bd7e74>] __do_syscall+0xf4/0x1a0
>  [ 6818.651680]  [<00047dd454c0db58>] system_call+0x70/0x98
> 
> As KASAN is a big user of stackdepot, the current DEPOT_POOLS_CAP of
> 8192 may not be enough. Double DEPOT_POOLS_CAP if KASAN is enabled to
> avoid hitting this problem.
> 
> Also use the MIN() macro for defining DEPOT_MAX_POOLS to clarify the
> intention.

We don't want earlier kernels doing this so I think

Fixes: 02754e0a484a ("lib/stackdepot.c: bump stackdepot capacity from 16MB to 128MB")
Cc: stable

Interestingly, 02754e0a484a bumped this from 1024 to 8192.

02754e0a484a may be wrong - perhaps the interaction with KASAN didn't
ewxist at that time.  Please take a look?