Re: slub: Lockout validation scans during freeing of object

From: Eric Dumazet
Date: Tue Nov 22 2011 - 12:21:32 EST

Le mardi 22 novembre 2011 Ã 10:53 -0600, Christoph Lameter a Ãcrit :
> A bit heavy handed locking but this should do the trick.
>
> Subject: slub: Lockout validation scans during freeing of object
>
> Slab validation can run right now while the slab free paths prepare
> the redzone fields etc around the objects in preparation of the
> actual freeing of the object. This can lead to false positives.
>
> Take the node lock unconditionally during free so that the validation
> can examine objects without them being disturbed by freeing operations.
>
> Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>
>
> ---
> mm/slub.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> Index: linux-2.6/mm/slub.c
> ===================================================================
> --- linux-2.6.orig/mm/slub.c 2011-11-22 10:42:19.000000000 -0600
> +++ linux-2.6/mm/slub.c 2011-11-22 10:44:34.000000000 -0600
> @@ -2391,8 +2391,15 @@ static void __slab_free(struct kmem_cach
>
> stat(s, FREE_SLOWPATH);
>
> - if (kmem_cache_debug(s) && !free_debug_processing(s, page, x, addr))
> - return;
> + if (kmem_cache_debug(s)) {
> +
> + /* Lock out any concurrent validate_slab calls */
> + n = get_node(s, page_to_nid(page));
> + spin_lock_irqsave(&n->list_lock, flags);
> +
> + if (!free_debug_processing(s, page, x, addr))
> + goto out;
> + }
>
> do {
> prior = page->freelist;
> @@ -2471,6 +2478,7 @@ static void __slab_free(struct kmem_cach
> stat(s, FREE_ADD_PARTIAL);
> }
> }
> +out:
> spin_unlock_irqrestore(&n->list_lock, flags);
> return;
>


This seems better, but I still have some warnings :

[ 162.117574] SLUB: selinux_inode_security 136 slabs counted but counter=137
[ 179.879907] SLUB: task_xstate 1 slabs counted but counter=2
[ 179.881745] SLUB: vm_area_struct 47 slabs counted but counter=48
[ 180.381964] SLUB: kmalloc-64 46 slabs counted but counter=47
[ 192.366437] SLUB: vm_area_struct 82 slabs counted but counter=83
[ 195.016732] SLUB: names_cache 3 slabs counted but counter=4
[ 196.073166] SLUB: dentry 623 slabs counted but counter=624
[ 196.093857] SLUB: names_cache 3 slabs counted but counter=4
[ 196.631420] SLUB: names_cache 5 slabs counted but counter=6
[ 198.760180] SLUB: kmalloc-16 30 slabs counted but counter=31
[ 198.773492] SLUB: names_cache 5 slabs counted but counter=6
[ 198.783637] SLUB: selinux_inode_security 403 slabs counted but counter=404
[ 201.717932] SLUB: filp 53 slabs counted but counter=54
[ 202.984756] SLUB: filp 40 slabs counted but counter=41
[ 203.819525] SLUB: task_xstate 3 slabs counted but counter=4
[ 205.699916] SLUB: cfq_io_context 1 slabs counted but counter=2
[ 206.526646] SLUB: skbuff_head_cache 4 slabs counted but counter=5
[ 208.431951] SLUB: names_cache 3 slabs counted but counter=4
[ 210.672056] SLUB: vm_area_struct 88 slabs counted but counter=89
[ 213.160055] SLUB: vm_area_struct 94 slabs counted but counter=95
[ 215.604856] SLUB: cfq_queue 1 slabs counted but counter=2
[ 217.872494] SLUB: filp 56 slabs counted but counter=57
[ 220.184599] SLUB: names_cache 3 slabs counted but counter=4
[ 221.783732] SLUB: anon_vma_chain 53 slabs counted but counter=54
[ 221.816662] SLUB: kmalloc-16 66 slabs counted but counter=67
[ 221.828582] SLUB: names_cache 3 slabs counted but counter=4
[ 221.848231] SLUB: vm_area_struct 99 slabs counted but counter=100
[ 224.125411] SLUB: kmalloc-16 30 slabs counted but counter=31
[ 224.126313] SLUB: kmalloc-16 67 slabs counted but counter=68
[ 224.138768] SLUB: names_cache 3 slabs counted but counter=4
[ 224.921409] SLUB: anon_vma 36 slabs counted but counter=37
[ 224.927833] SLUB: buffer_head 294 slabs counted but counter=295
[ 226.473891] SLUB: kmalloc-16 67 slabs counted but counter=68
[ 228.801716] SLUB: names_cache 5 slabs counted but counter=6
[ 229.610225] SLUB: filp 47 slabs counted but counter=48
[ 232.050811] SLUB: filp 53 slabs counted but counter=54
[ 235.835888] SLUB: names_cache 3 slabs counted but counter=4
[ 236.625318] SLUB: filp 48 slabs counted but counter=49
[ 236.634563] SLUB: kmalloc-16 30 slabs counted but counter=31
[ 236.635667] SLUB: kmalloc-16 67 slabs counted but counter=68
[ 237.500016] SLUB: radix_tree_node 100 slabs counted but counter=101
[ 238.248677] SLUB: filp 48 slabs counted but counter=49
[ 239.097674] SLUB: filp 49 slabs counted but counter=50
[ 239.975020] SLUB: names_cache 3 slabs counted but counter=4
[ 241.569766] SLUB: vm_area_struct 102 slabs counted but counter=103
[ 242.388502] SLUB: names_cache 5 slabs counted but counter=6
[ 243.152519] SLUB: anon_vma_chain 56 slabs counted but counter=57
[ 245.661970] SLUB: filp 49 slabs counted but counter=50
[ 247.298004] SLUB: filp 48 slabs counted but counter=50
[ 248.851148] SLUB: journal_handle 3 slabs counted but counter=4
[ 249.674320] SLUB: names_cache 3 slabs counted but counter=4
[ 250.414476] SLUB: bio-0 24 slabs counted but counter=25
[ 250.461655] SLUB: kmalloc-96 49 slabs counted but counter=50
[ 250.477188] SLUB: sgpool-16 0 slabs counted but counter=1
[ 251.298554] SLUB: kmalloc-32 9 slabs counted but counter=10
[ 252.096119] SLUB: names_cache 3 slabs counted but counter=4
[ 256.179892] SLUB: filp 58 slabs counted but counter=59
[ 256.188385] SLUB: kmalloc-16 30 slabs counted but counter=31
[ 257.040508] SLUB: kmalloc-16 30 slabs counted but counter=31
[ 258.704236] SLUB: buffer_head 502 slabs counted but counter=503
[ 258.745777] SLUB: kmalloc-32 9 slabs counted but counter=10
[ 258.752285] SLUB: names_cache 3 slabs counted but counter=4
[ 260.412312] SLUB: filp 54 slabs counted but counter=56
[ 261.213526] SLUB: filp 44 slabs counted but counter=45
[ 262.846810] SLUB: kmalloc-16 31 slabs counted but counter=32
[ 262.859062] SLUB: names_cache 5 slabs counted but counter=6
[ 262.881728] SLUB: task_xstate 3 slabs counted but counter=4
[ 263.672055] SLUB: filp 54 slabs counted but counter=55
[ 266.191191] SLUB: kmalloc-16 30 slabs counted but counter=31
[ 266.203799] SLUB: names_cache 5 slabs counted but counter=6
[ 268.486964] SLUB: filp 52 slabs counted but counter=53
[ 268.509446] SLUB: names_cache 5 slabs counted but counter=6
[ 269.365745] SLUB: vm_area_struct 88 slabs counted but counter=89



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