Commit 7edd7e82 authored by Waiman Long's avatar Waiman Long Committed by Greg Kroah-Hartman
Browse files

console: Move userspace I/O out of console_lock to fix lockdep warning 



When running certain workload on a debug kernel with lockdep turned on,
a ppc64 kvm guest could sometimes hit the following lockdep warning:

  [ INFO: possible circular locking dependency detected ]
  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(&mm->mmap_sem);
                                lock(console_lock);
                                lock(&mm->mmap_sem);
   lock(cpu_hotplug.lock);

  *** DEADLOCK ***

Looking at the console code, the console_lock-->mmap_sem scenario will
only happen when reading or writing the console unicode map leading to
a page fault.

To break this circular locking dependency, all the userspace I/O
operations in consolemap.c are now moved outside of the console_lock
critical sections so that the mmap_sem won't be acquired when holding
the console_lock.

Signed-off-by: default avatarWaiman Long <longman@redhat.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 5020ded7

drivers/tty/vt/consolemap.c

+74 −41
Original line number Diff line number Diff line
@@ -9,6 +9,17 @@ 
 * Support for multiple unimaps by Jakub Jelinek <jj@ultra.linux.cz>, July 1998

 *

 * Fix bug in inverse translation. Stanislav Voronyi <stas@cnti.uanet.kharkov.ua>, Dec 1998

 *

 * In order to prevent the following circular lock dependency:

 *   &mm->mmap_sem --> cpu_hotplug.lock --> console_lock --> &mm->mmap_sem

 *

 * We cannot allow page fault to happen while holding the console_lock.

 * Therefore, all the userspace copy operations have to be done outside

 * the console_lock critical sections.

 *

 * As all the affected functions are all called directly from vt_ioctl(), we

 * can allocate some small buffers directly on stack without worrying about

 * stack overflow.

 */



#include <linux/module.h>
@@ -22,6 +33,7 @@ 
#include <linux/console.h>

#include <linux/consolemap.h>

#include <linux/vt_kern.h>

#include <linux/string.h>



static unsigned short translations[][256] = {

  /* 8-bit Latin-1 mapped to Unicode -- trivial mapping */
@@ -309,18 +321,19 @@ static void update_user_maps(void) 
int con_set_trans_old(unsigned char __user * arg)

{

	int i;

	unsigned short *p = translations[USER_MAP];

	unsigned short inbuf[E_TABSZ];



	if (!access_ok(VERIFY_READ, arg, E_TABSZ))

		return -EFAULT;



	console_lock();

	for (i = 0; i < E_TABSZ ; i++) {

		unsigned char uc;

		__get_user(uc, arg+i);

		p[i] = UNI_DIRECT_BASE | uc;

		inbuf[i] = UNI_DIRECT_BASE | uc;

	}



	console_lock();

	memcpy(translations[USER_MAP], inbuf, sizeof(inbuf));

	update_user_maps();

	console_unlock();

	return 0;
@@ -330,6 +343,7 @@ int con_get_trans_old(unsigned char __user * arg) 
{

	int i, ch;

	unsigned short *p = translations[USER_MAP];

	unsigned char outbuf[E_TABSZ];



	if (!access_ok(VERIFY_WRITE, arg, E_TABSZ))

		return -EFAULT;
@@ -338,27 +352,28 @@ int con_get_trans_old(unsigned char __user * arg) 
	for (i = 0; i < E_TABSZ ; i++)

	{

		ch = conv_uni_to_pc(vc_cons[fg_console].d, p[i]);

		__put_user((ch & ~0xff) ? 0 : ch, arg+i);

		outbuf[i] = (ch & ~0xff) ? 0 : ch;

	}

	console_unlock();



	for (i = 0; i < E_TABSZ ; i++)

		__put_user(outbuf[i], arg+i);

	return 0;

}



int con_set_trans_new(ushort __user * arg)

{

	int i;

	unsigned short *p = translations[USER_MAP];

	unsigned short inbuf[E_TABSZ];



	if (!access_ok(VERIFY_READ, arg, E_TABSZ*sizeof(unsigned short)))

		return -EFAULT;



	console_lock();

	for (i=0; i<E_TABSZ ; i++) {

		unsigned short us;

		__get_user(us, arg+i);

		p[i] = us;

	}

	for (i = 0; i < E_TABSZ ; i++)

		__get_user(inbuf[i], arg+i);



	console_lock();

	memcpy(translations[USER_MAP], inbuf, sizeof(inbuf));

	update_user_maps();

	console_unlock();

	return 0;
@@ -367,16 +382,17 @@ int con_set_trans_new(ushort __user * arg) 
int con_get_trans_new(ushort __user * arg)

{

	int i;

	unsigned short *p = translations[USER_MAP];

	unsigned short outbuf[E_TABSZ];



	if (!access_ok(VERIFY_WRITE, arg, E_TABSZ*sizeof(unsigned short)))

		return -EFAULT;



	console_lock();

	for (i=0; i<E_TABSZ ; i++)

	  __put_user(p[i], arg+i);

	memcpy(outbuf, translations[USER_MAP], sizeof(outbuf));

	console_unlock();



	for (i = 0; i < E_TABSZ ; i++)

		__put_user(outbuf[i], arg+i);

	return 0;

}
@@ -536,10 +552,20 @@ int con_set_unimap(struct vc_data *vc, ushort ct, struct unipair __user *list) 
{

	int err = 0, err1, i;

	struct uni_pagedir *p, *q;

	struct unipair *unilist, *plist;



	if (!ct)

		return 0;



	unilist = kmalloc_array(ct, sizeof(struct unipair), GFP_KERNEL);

	if (!unilist)

		return -ENOMEM;



	for (i = ct, plist = unilist; i; i--, plist++, list++) {

		__get_user(plist->unicode, &list->unicode);

		__get_user(plist->fontpos, &list->fontpos);

	}



	console_lock();



	/* Save original vc_unipagdir_loc in case we allocate a new one */
@@ -557,8 +583,8 @@ int con_set_unimap(struct vc_data *vc, ushort ct, struct unipair __user *list) 
		

		err1 = con_do_clear_unimap(vc);

		if (err1) {

			console_unlock();

			return err1;

			err = err1;

			goto out_unlock;

		}

		

		/*
@@ -592,8 +618,8 @@ int con_set_unimap(struct vc_data *vc, ushort ct, struct unipair __user *list) 
						*vc->vc_uni_pagedir_loc = p;

						con_release_unimap(q);

						kfree(q);

						console_unlock();

						return err1; 

						err = err1;

						goto out_unlock;

					}

				}

			} else {
@@ -617,22 +643,17 @@ int con_set_unimap(struct vc_data *vc, ushort ct, struct unipair __user *list) 
	/*

	 * Insert user specified unicode pairs into new table.

	 */

	while (ct--) {

		unsigned short unicode, fontpos;

		__get_user(unicode, &list->unicode);

		__get_user(fontpos, &list->fontpos);

		if ((err1 = con_insert_unipair(p, unicode,fontpos)) != 0)

	for (plist = unilist; ct; ct--, plist++) {

		err1 = con_insert_unipair(p, plist->unicode, plist->fontpos);

		if (err1)

			err = err1;

		list++;

	}

	

	/*

	 * Merge with fontmaps of any other virtual consoles.

	 */

	if (con_unify_unimap(vc, p)) {

		console_unlock();

		return err;

	}

	if (con_unify_unimap(vc, p))

		goto out_unlock;



	for (i = 0; i <= 3; i++)

		set_inverse_transl(vc, p, i); /* Update inverse translations */
@@ -640,6 +661,7 @@ int con_set_unimap(struct vc_data *vc, ushort ct, struct unipair __user *list) 


out_unlock:

	console_unlock();

	kfree(unilist);

	return err;

}
@@ -735,9 +757,15 @@ EXPORT_SYMBOL(con_copy_unimap); 
 */

int con_get_unimap(struct vc_data *vc, ushort ct, ushort __user *uct, struct unipair __user *list)

{

	int i, j, k, ect;

	int i, j, k;

	ushort ect;

	u16 **p1, *p2;

	struct uni_pagedir *p;

	struct unipair *unilist, *plist;



	unilist = kmalloc_array(ct, sizeof(struct unipair), GFP_KERNEL);

	if (!unilist)

		return -ENOMEM;



	console_lock();
@@ -750,21 +778,26 @@ int con_get_unimap(struct vc_data *vc, ushort ct, ushort __user *uct, struct uni 
			for (j = 0; j < 32; j++) {

			p2 = *(p1++);

			if (p2)

				for (k = 0; k < 64; k++) {

					if (*p2 < MAX_GLYPH && ect++ < ct) {

						__put_user((u_short)((i<<11)+(j<<6)+k),

							   &list->unicode);

						__put_user((u_short) *p2, 

							   &list->fontpos);

						list++;

				for (k = 0; k < 64; k++, p2++) {

					if (*p2 >= MAX_GLYPH)

						continue;

					if (ect < ct) {

						unilist[ect].unicode =

							(i<<11)+(j<<6)+k;

						unilist[ect].fontpos = *p2;

					}

					p2++;

					ect++;

				}

			}

		}

	}

	__put_user(ect, uct);

	console_unlock();

	for (i = min(ect, ct), plist = unilist; i; i--, list++, plist++) {

		__put_user(plist->unicode, &list->unicode);

		__put_user(plist->fontpos, &list->fontpos);

	}

	__put_user(ect, uct);

	kfree(unilist);

	return ((ect <= ct) ? 0 : -ENOMEM);

}

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