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    SubjectSerious bugs in kernel - related to misuse of GFP_ATOMIC
    Hi!

    All linux users are worried of 'Could not get a free page'. I keep
    telling them that it is normal and that kernel should handle that.

    PLEASE, David or Linus, tell me I'm right:

    Anyone, who kmalloc's with priority of GFP_ATOMIC must be ready to get
    NULL, as it is perfectly legal (it should not happen too often, but it
    can happen, sometimes; if GFP_ATOMIC allocation fails, it should lead
    only to some slowdown.)

    So I created a small patch: It artifically makes about 1/2 of atomic
    allocations to fail. (Cruel, is not it?)

    Well, and I seen this (random) problems: [Note, that all of them may
    happen anytime to anyone]

    * System failed to start init. No message given.
    * /proc fails to mount. Silently.
    * Obvious bug in arp_alloc causes Oops. (patch below)
    * Can not lock lock file /etc/mtab (or something similar)
    * rpc.nfsd locked up
    * syslogd locked up

    I also added code I used for my test. Maybe 1/2 of failed allocations
    is too much for normal use, but it is _really_ good for test, and IMO
    this should be included in development kernel so writers of drivers
    could test them under weird circumstances etc.

    Pavel

    Testing patch:

    Index: linux/arch/i386/config.in
    ===================================================================
    RCS file: /home/pavel/cvsroot/linux/arch/i386/config.in,v
    retrieving revision 1.10
    diff -u -r1.10 config.in
    --- config.in 1997/09/07 16:20:43 1.10
    +++ config.in 1997/09/17 21:57:55
    @@ -107,6 +107,7 @@
    bool 'SMP Profiling' CONFIG_SMP_PROF
    fi
    bool 'Magic SysRq key' CONFIG_MAGIC_SYSRQ
    +bool 'Unreliable kmalloc' CONFIG_UNRELIABLE_MALLOC
    endmenu


    Index: linux/mm/slab.c
    ===================================================================
    RCS file: /home/pavel/cvsroot/linux/mm/slab.c,v
    retrieving revision 1.5
    diff -u -r1.5 slab.c
    --- slab.c 1997/08/16 17:04:13 1.5
    +++ slab.c 1997/09/17 21:58:31
    @@ -1358,7 +1358,12 @@
    kmem_bufctl_t *bufp;
    void *objp;
    unsigned long save_flags;
    -
    +#ifdef CONFIG_UNRELIABLE_MALLOC
    +#define RANDOM (! (jiffies & 1))
    + if ((flags & SLAB_LEVEL_MASK) == SLAB_ATOMIC)
    + if (RANDOM)
    + return NULL;
    +#endif
    /* Sanity check. */
    if (!cachep)
    goto nul_ptr;
    Small patch for obvious bug in arp.c:

    Index: linux/net/ipv4/arp.c
    ===================================================================
    RCS file: /home/pavel/cvsroot/linux/net/ipv4/arp.c,v
    retrieving revision 1.2
    diff -u -r1.2 arp.c
    --- arp.c 1997/06/09 15:01:11 1.2
    +++ arp.c 1997/09/17 21:58:32
    @@ -797,10 +797,11 @@

    entry = (struct arp_table *)neigh_alloc(sizeof(struct arp_table),
    &arp_neigh_ops);
    - atomic_set(&entry->u.neigh.refcnt, 1);

    if (entry != NULL)
    {
    + atomic_set(&entry->u.neigh.refcnt, 1);
    +
    if (how)
    atomic_inc(&arp_size);


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