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    Subject[PATCH 3/3 V2] slab,rcu: don't assume the size of struct rcu_head
    The size of struct rcu_head may be changed. When it becomes larger,
    it may pollute the data after struct slab.

    Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
    ---
    diff --git a/mm/slab.c b/mm/slab.c
    index 37961d1..52cf0b4 100644
    --- a/mm/slab.c
    +++ b/mm/slab.c
    @@ -191,22 +191,6 @@ typedef unsigned int kmem_bufctl_t;
    #define SLAB_LIMIT (((kmem_bufctl_t)(~0U))-3)

    /*
    - * struct slab
    - *
    - * Manages the objs in a slab. Placed either at the beginning of mem allocated
    - * for a slab, or allocated from an general cache.
    - * Slabs are chained into three list: fully used, partial, fully free slabs.
    - */
    -struct slab {
    - struct list_head list;
    - unsigned long colouroff;
    - void *s_mem; /* including colour offset */
    - unsigned int inuse; /* num of objs active in slab */
    - kmem_bufctl_t free;
    - unsigned short nodeid;
    -};
    -
    -/*
    * struct slab_rcu
    *
    * slab_destroy on a SLAB_DESTROY_BY_RCU cache uses this structure to
    @@ -219,8 +203,6 @@ struct slab {
    *
    * rcu_read_lock before reading the address, then rcu_read_unlock after
    * taking the spinlock within the structure expected at that address.
    - *
    - * We assume struct slab_rcu can overlay struct slab when destroying.
    */
    struct slab_rcu {
    struct rcu_head head;
    @@ -229,6 +211,27 @@ struct slab_rcu {
    };

    /*
    + * struct slab
    + *
    + * Manages the objs in a slab. Placed either at the beginning of mem allocated
    + * for a slab, or allocated from an general cache.
    + * Slabs are chained into three list: fully used, partial, fully free slabs.
    + */
    +struct slab {
    + union {
    + struct {
    + struct list_head list;
    + unsigned long colouroff;
    + void *s_mem; /* including colour offset */
    + unsigned int inuse; /* num of objs active in slab */
    + kmem_bufctl_t free;
    + unsigned short nodeid;
    + };
    + struct slab_rcu __slab_cover_slab_rcu;
    + };
    +};
    +
    +/*
    * struct array_cache
    *
    * Purpose:
    --

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