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Commit 6345d24d authored by Linus Torvalds's avatar Linus Torvalds
Browse files

mm: Fix boot crash in mm_alloc() 



Thomas Gleixner reports that we now have a boot crash triggered by
CONFIG_CPUMASK_OFFSTACK=y:

    BUG: unable to handle kernel NULL pointer dereference at   (null)
    IP: [<c11ae035>] find_next_bit+0x55/0xb0
    Call Trace:
     [<c11addda>] cpumask_any_but+0x2a/0x70
     [<c102396b>] flush_tlb_mm+0x2b/0x80
     [<c1022705>] pud_populate+0x35/0x50
     [<c10227ba>] pgd_alloc+0x9a/0xf0
     [<c103a3fc>] mm_init+0xec/0x120
     [<c103a7a3>] mm_alloc+0x53/0xd0

which was introduced by commit de03c72c ("mm: convert
mm->cpu_vm_cpumask into cpumask_var_t"), and is due to wrong ordering of
mm_init() vs mm_init_cpumask

Thomas wrote a patch to just fix the ordering of initialization, but I
hate the new double allocation in the fork path, so I ended up instead
doing some more radical surgery to clean it all up.

Reported-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reported-by: default avatarIngo Molnar <mingo@elte.hu>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent cab0d85c

include/linux/mm_types.h

+12 −2
Original line number Diff line number Diff line
@@ -264,6 +264,8 @@ struct mm_struct { 


	struct linux_binfmt *binfmt;



	cpumask_var_t cpu_vm_mask_var;



	/* Architecture-specific MM context */

	mm_context_t context;
@@ -311,10 +313,18 @@ struct mm_struct { 
#ifdef CONFIG_TRANSPARENT_HUGEPAGE

	pgtable_t pmd_huge_pte; /* protected by page_table_lock */

#endif



	cpumask_var_t cpu_vm_mask_var;

#ifdef CONFIG_CPUMASK_OFFSTACK

	struct cpumask cpumask_allocation;

#endif

};



static inline void mm_init_cpumask(struct mm_struct *mm)

{

#ifdef CONFIG_CPUMASK_OFFSTACK

	mm->cpu_vm_mask_var = &mm->cpumask_allocation;

#endif

}



/* Future-safe accessor for struct mm_struct's cpu_vm_mask. */

static inline cpumask_t *mm_cpumask(struct mm_struct *mm)

{

include/linux/sched.h

+0 −1
Original line number Diff line number Diff line
@@ -2194,7 +2194,6 @@ static inline void mmdrop(struct mm_struct * mm) 
	if (unlikely(atomic_dec_and_test(&mm->mm_count)))

		__mmdrop(mm);

}

extern int mm_init_cpumask(struct mm_struct *mm, struct mm_struct *oldmm);



/* mmput gets rid of the mappings and all user-space */

extern void mmput(struct mm_struct *);

init/main.c

+1 −1
Original line number Diff line number Diff line
@@ -487,6 +487,7 @@ asmlinkage void __init start_kernel(void) 
	printk(KERN_NOTICE "%s", linux_banner);

	setup_arch(&command_line);

	mm_init_owner(&init_mm, &init_task);

	mm_init_cpumask(&init_mm);

	setup_command_line(command_line);

	setup_nr_cpu_ids();

	setup_per_cpu_areas();
@@ -510,7 +511,6 @@ asmlinkage void __init start_kernel(void) 
	sort_main_extable();

	trap_init();

	mm_init();

	BUG_ON(mm_init_cpumask(&init_mm, 0));



	/*

	 * Set up the scheduler prior starting any interrupts (such as the

kernel/fork.c

+10 −32
Original line number Diff line number Diff line
@@ -484,20 +484,6 @@ static void mm_init_aio(struct mm_struct *mm) 
#endif

}



int mm_init_cpumask(struct mm_struct *mm, struct mm_struct *oldmm)

{

#ifdef CONFIG_CPUMASK_OFFSTACK

	if (!alloc_cpumask_var(&mm->cpu_vm_mask_var, GFP_KERNEL))

		return -ENOMEM;



	if (oldmm)

		cpumask_copy(mm_cpumask(mm), mm_cpumask(oldmm));

	else

		memset(mm_cpumask(mm), 0, cpumask_size());

#endif

	return 0;

}



static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p)

{

	atomic_set(&mm->mm_users, 1);
@@ -538,17 +524,8 @@ struct mm_struct * mm_alloc(void) 
		return NULL;



	memset(mm, 0, sizeof(*mm));

	mm = mm_init(mm, current);

	if (!mm)

		return NULL;



	if (mm_init_cpumask(mm, NULL)) {

		mm_free_pgd(mm);

		free_mm(mm);

		return NULL;

	}



	return mm;

	mm_init_cpumask(mm);

	return mm_init(mm, current);

}



/*
@@ -559,7 +536,6 @@ struct mm_struct * mm_alloc(void) 
void __mmdrop(struct mm_struct *mm)

{

	BUG_ON(mm == &init_mm);

	free_cpumask_var(mm->cpu_vm_mask_var);

	mm_free_pgd(mm);

	destroy_context(mm);

	mmu_notifier_mm_destroy(mm);
@@ -753,6 +729,7 @@ struct mm_struct *dup_mm(struct task_struct *tsk) 
		goto fail_nomem;



	memcpy(mm, oldmm, sizeof(*mm));

	mm_init_cpumask(mm);



	/* Initializing for Swap token stuff */

	mm->token_priority = 0;
@@ -765,9 +742,6 @@ struct mm_struct *dup_mm(struct task_struct *tsk) 
	if (!mm_init(mm, tsk))

		goto fail_nomem;



	if (mm_init_cpumask(mm, oldmm))

		goto fail_nocpumask;



	if (init_new_context(tsk, mm))

		goto fail_nocontext;
@@ -794,9 +768,6 @@ struct mm_struct *dup_mm(struct task_struct *tsk) 
	return NULL;



fail_nocontext:

	free_cpumask_var(mm->cpu_vm_mask_var);



fail_nocpumask:

	/*

	 * If init_new_context() failed, we cannot use mmput() to free the mm

	 * because it calls destroy_context()
@@ -1591,6 +1562,13 @@ void __init proc_caches_init(void) 
	fs_cachep = kmem_cache_create("fs_cache",

			sizeof(struct fs_struct), 0,

			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);

	/*

	 * FIXME! The "sizeof(struct mm_struct)" currently includes the

	 * whole struct cpumask for the OFFSTACK case. We could change

	 * this to *only* allocate as much of it as required by the

	 * maximum number of CPU's we can ever have.  The cpumask_allocation

	 * is at the end of the structure, exactly for that reason.

	 */

	mm_cachep = kmem_cache_create("mm_struct",

			sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,

			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);