Re: [patch 5/5] oom: invoke OOM killer from pagefault handler

[Kirill Korotaev]

Nick,

AFAICS, 1 page allocation which is done in page fault handler
can fail in the only case - OOM kills current, so if we failed
we should have TIF_MEMDIE and just kill current.
Selecting another process for killing if page fault fails means
taking another victim with the one being already killed.

my 2 cents.

Thanks,
Kirill

> Rather than have the pagefault handler kill a process directly if it gets a
> VM_FAULT_OOM, have it call into the OOM killer.
> 
> Only converted a few architectures so far - this is just an RFC.
> 
> Index: linux-2.6/mm/oom_kill.c
> ===================================================================
> --- linux-2.6.orig/mm/oom_kill.c
> +++ linux-2.6/mm/oom_kill.c
> @@ -376,6 +376,57 @@ int unregister_oom_notifier(struct notif
>  }
>  EXPORT_SYMBOL_GPL(unregister_oom_notifier);
>  
> +/*
> + * Must be called with cpuset_lock and tasklist_lock held for read.
> + */
> +void __out_of_memory(void)
> +{
> +	unsigned long points = 0;
> +	struct task_struct *p;
> +
> +	if (sysctl_panic_on_oom)
> +		panic("out of memory. panic_on_oom is selected\n");
> +retry:
> +	/*
> +	 * Rambo mode: Shoot down a process and hope it solves whatever
> +	 * issues we may have.
> +	 */
> +	p = select_bad_process(&points);
> +
> +	if (PTR_ERR(p) == -1UL)
> +		return;
> +
> +	/* Found nothing?!?! Either we hang forever, or we panic. */
> +	if (!p) {
> +		read_unlock(&tasklist_lock);
> +		cpuset_unlock();
> +		panic("Out of memory and no killable processes...\n");
> +	}
> +
> +	if (oom_kill_process(p, points, "Out of memory"))
> +		goto retry;
> +}
> +
> +/*
> + * pagefault handler calls into here because it is out of memory but
> + * doesn't know exactly how or why.
> + */
> +void pagefault_out_of_memory(void)
> +{
> +	if (printk_ratelimit()) {
> +		printk(KERN_WARNING "%s invoked oom-killer from pagefault: "
> +			"oomkilladj=%d\n", current->oomkilladj);
> +		dump_stack();
> +		show_mem();
> +	}
> +
> +	cpuset_lock();
> +	read_lock(&tasklist_lock);
> +	__out_of_memory();
> +	read_unlock(&tasklist_lock);
> +	cpuset_unlock();
> +}
> +
>  /**
>   * out_of_memory - kill the "best" process when we run out of memory
>   *
> @@ -386,8 +437,6 @@ EXPORT_SYMBOL_GPL(unregister_oom_notifie
>   */
>  void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order)
>  {
> -	struct task_struct *p;
> -	unsigned long points = 0;
>  	unsigned long freed = 0;
>  
>  	blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
> @@ -412,42 +461,18 @@ void out_of_memory(struct zonelist *zone
>  	 */
>  	switch (constrained_alloc(zonelist, gfp_mask)) {
>  	case CONSTRAINT_MEMORY_POLICY:
> -		oom_kill_process(current, points,
> -				"No available memory (MPOL_BIND)");
> +		oom_kill_process(current, 0, "No available memory (MPOL_BIND)");
>  		break;
>  
>  	case CONSTRAINT_CPUSET:
> -		oom_kill_process(current, points,
> -				"No available memory in cpuset");
> +		oom_kill_process(current, 0, "No available memory in cpuset");
>  		break;
>  
>  	case CONSTRAINT_NONE:
> -		if (sysctl_panic_on_oom)
> -			panic("out of memory. panic_on_oom is selected\n");
> -retry:
> -		/*
> -		 * Rambo mode: Shoot down a process and hope it solves whatever
> -		 * issues we may have.
> -		 */
> -		p = select_bad_process(&points);
> -
> -		if (PTR_ERR(p) == -1UL)
> -			goto out;
> -
> -		/* Found nothing?!?! Either we hang forever, or we panic. */
> -		if (!p) {
> -			read_unlock(&tasklist_lock);
> -			cpuset_unlock();
> -			panic("Out of memory and no killable processes...\n");
> -		}
> -
> -		if (oom_kill_process(p, points, "Out of memory"))
> -			goto retry;
> -
> +		__out_of_memory();
>  		break;
>  	}
>  
> -out:
>  	read_unlock(&tasklist_lock);
>  	cpuset_unlock();
>  
> Index: linux-2.6/arch/alpha/mm/fault.c
> ===================================================================
> --- linux-2.6.orig/arch/alpha/mm/fault.c
> +++ linux-2.6/arch/alpha/mm/fault.c
> @@ -143,7 +143,6 @@ do_page_fault(unsigned long address, uns
>  			goto bad_area;
>  	}
>  
> - survive:
>  	/* If for any reason at all we couldn't handle the fault,
>  	   make sure we exit gracefully rather than endlessly redo
>  	   the fault.  */
> @@ -190,19 +189,13 @@ do_page_fault(unsigned long address, uns
>  	die_if_kernel("Oops", regs, cause, (unsigned long*)regs - 16);
>  	do_exit(SIGKILL);
>  
> -	/* We ran out of memory, or some other thing happened to us that
> -	   made us unable to handle the page fault gracefully.  */
> +	/*
> +	 * We ran out of memory, call the OOM killer, and return to userspace
> +	 * (the fault will be retried if we weren't killed)
> +	 */
>   out_of_memory:
> -	if (is_init(current)) {
> -		yield();
> -		down_read(&mm->mmap_sem);
> -		goto survive;
> -	}
> -	printk(KERN_ALERT "VM: killing process %s(%d)\n",
> -	       current->comm, current->pid);
> -	if (!user_mode(regs))
> -		goto no_context;
> -	do_exit(SIGKILL);
> +	pagefault_out_of_memory();
> +	return;
>  
>   do_sigbus:
>  	/* Send a sigbus, regardless of whether we were in kernel
> Index: linux-2.6/arch/i386/mm/fault.c
> ===================================================================
> --- linux-2.6.orig/arch/i386/mm/fault.c
> +++ linux-2.6/arch/i386/mm/fault.c
> @@ -444,7 +444,6 @@ good_area:
>  				goto bad_area;
>  	}
>  
> - survive:
>  	/*
>  	 * If for any reason at all we couldn't handle the fault,
>  	 * make sure we exit gracefully rather than endlessly redo
> @@ -583,21 +582,14 @@ no_context:
>  	bust_spinlocks(0);
>  	do_exit(SIGKILL);
>  
> -/*
> - * We ran out of memory, or some other thing happened to us that made
> - * us unable to handle the page fault gracefully.
> - */
>  out_of_memory:
> +	/*
> +	 * We ran out of memory, call the OOM killer, and return to userspace
> +	 * (the fault will be retried if we weren't killed)
> +	 */
>  	up_read(&mm->mmap_sem);
> -	if (is_init(tsk)) {
> -		yield();
> -		down_read(&mm->mmap_sem);
> -		goto survive;
> -	}
> -	printk("VM: killing process %s\n", tsk->comm);
> -	if (error_code & 4)
> -		do_exit(SIGKILL);
> -	goto no_context;
> +	pagefault_out_of_memory();
> +	return;
>  
>  do_sigbus:
>  	up_read(&mm->mmap_sem);
> Index: linux-2.6/arch/ia64/mm/fault.c
> ===================================================================
> --- linux-2.6.orig/arch/ia64/mm/fault.c
> +++ linux-2.6/arch/ia64/mm/fault.c
> @@ -155,7 +155,6 @@ ia64_do_page_fault (unsigned long addres
>  	if ((vma->vm_flags & mask) != mask)
>  		goto bad_area;
>  
> -  survive:
>  	/*
>  	 * If for any reason at all we couldn't handle the fault, make
>  	 * sure we exit gracefully rather than endlessly redo the
> @@ -280,13 +279,10 @@ ia64_do_page_fault (unsigned long addres
>  
>    out_of_memory:
>  	up_read(&mm->mmap_sem);
> -	if (is_init(current)) {
> -		yield();
> -		down_read(&mm->mmap_sem);
> -		goto survive;
> -	}
> -	printk(KERN_CRIT "VM: killing process %s\n", current->comm);
> -	if (user_mode(regs))
> -		do_exit(SIGKILL);
> -	goto no_context;
> +	/*
> +	 * We ran out of memory, call the OOM killer, and return to userspace
> +	 * (the fault will be retried if we weren't killed)
> +	 */
> +	pagefault_out_of_memory();
> +	return;
>  }
> Index: linux-2.6/arch/powerpc/mm/fault.c
> ===================================================================
> --- linux-2.6.orig/arch/powerpc/mm/fault.c
> +++ linux-2.6/arch/powerpc/mm/fault.c
> @@ -342,7 +342,6 @@ good_area:
>  	 * make sure we exit gracefully rather than endlessly redo
>  	 * the fault.
>  	 */
> - survive:
>  	switch (handle_mm_fault(mm, vma, address, is_write)) {
>  
>  	case VM_FAULT_MINOR:
> @@ -380,21 +379,14 @@ bad_area_nosemaphore:
>  
>  	return SIGSEGV;
>  
> -/*
> - * We ran out of memory, or some other thing happened to us that made
> - * us unable to handle the page fault gracefully.
> - */
>  out_of_memory:
> +	/*
> +	 * We ran out of memory, call the OOM killer, and return to userspace
> +	 * (the fault will be retried if we weren't killed)
> +	 */
>  	up_read(&mm->mmap_sem);
> -	if (is_init(current)) {
> -		yield();
> -		down_read(&mm->mmap_sem);
> -		goto survive;
> -	}
> -	printk("VM: killing process %s\n", current->comm);
> -	if (user_mode(regs))
> -		do_exit(SIGKILL);
> -	return SIGKILL;
> +	pagefault_out_of_memory();
> +	return 0;
>  
>  do_sigbus:
>  	up_read(&mm->mmap_sem);
> Index: linux-2.6/arch/x86_64/mm/fault.c
> ===================================================================
> --- linux-2.6.orig/arch/x86_64/mm/fault.c
> +++ linux-2.6/arch/x86_64/mm/fault.c
> @@ -407,7 +407,6 @@ asmlinkage void __kprobes do_page_fault(
>  	if (unlikely(in_atomic() || !mm))
>  		goto bad_area_nosemaphore;
>  
> - again:
>  	/* When running in the kernel we expect faults to occur only to
>  	 * addresses in user space.  All other faults represent errors in the
>  	 * kernel and should generate an OOPS.  Unfortunatly, in the case of an
> @@ -574,20 +573,14 @@ no_context:
>  	oops_end(flags);
>  	do_exit(SIGKILL);
>  
> -/*
> - * We ran out of memory, or some other thing happened to us that made
> - * us unable to handle the page fault gracefully.
> - */
>  out_of_memory:
> +	/*
> +	 * We ran out of memory, call the OOM killer, and return to userspace
> +	 * (the fault will be retried if we weren't killed)
> +	 */
>  	up_read(&mm->mmap_sem);
> -	if (is_init(current)) {
> -		yield();
> -		goto again;
> -	}
> -	printk("VM: killing process %s\n", tsk->comm);
> -	if (error_code & 4)
> -		do_exit(SIGKILL);
> -	goto no_context;
> +	pagefault_out_of_memory();
> +	return;
>  
>  do_sigbus:
>  	up_read(&mm->mmap_sem);
> Index: linux-2.6/include/linux/mm.h
> ===================================================================
> --- linux-2.6.orig/include/linux/mm.h
> +++ linux-2.6/include/linux/mm.h
> @@ -617,6 +617,11 @@ static inline int page_mapped(struct pag
>   */
>  #define VM_FAULT_WRITE	0x10
>  
> +/*
> + * Can be called by the pagefault handler when it gets a VM_FAULT_OOM.
> + */
> +extern void pagefault_out_of_memory(void);
> +
>  #define offset_in_page(p)	((unsigned long)(p) & ~PAGE_MASK)
>  
>  extern void show_free_areas(void);
> Index: linux-2.6/arch/um/kernel/trap.c
> ===================================================================
> --- linux-2.6.orig/arch/um/kernel/trap.c
> +++ linux-2.6/arch/um/kernel/trap.c
> @@ -75,7 +75,6 @@ good_area:
>                  goto out;
>  
>  	do {
> -survive:
>  		switch (handle_mm_fault(mm, vma, address, is_write)){
>  		case VM_FAULT_MINOR:
>  			current->min_flt++;
> @@ -119,13 +118,13 @@ out_nosemaphore:
>   * us unable to handle the page fault gracefully.
>   */
>  out_of_memory:
> -	if (is_init(current)) {
> -		up_read(&mm->mmap_sem);
> -		yield();
> -		down_read(&mm->mmap_sem);
> -		goto survive;
> -	}
> -	goto out;
> +	/*
> +	 * We ran out of memory, call the OOM killer, and return to userspace
> +	 * (the fault will be retried if we weren't killed)
> +	 */
> +	up_read(&mm->mmap_sem);
> +	pagefault_out_of_memory();
> +	goto out_nosemaphore;
>  }
>  
>  void segv_handler(int sig, union uml_pt_regs *regs)
> -
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