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: Waiman Long <longman@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 74 insertions, 41 deletions

diff --git a/drivers/tty/vt/consolemap.c b/drivers/tty/vt/consolemap.c
index 9d7ab7b66a8a..71e81406ef71 100644
--- a/drivers/tty/vt/consolemap.c
+++ b/drivers/tty/vt/consolemap.c
@@ -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++) {
+        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;
@@ -330,35 +343,37 @@ 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;
 
         console_lock();
-        for (i=0; i<E_TABSZ ; i++)
+        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);
 }