dm_create_session() calls create_proc_entry() with spinlock held

dm_create_session() calls create_proc_read_entry() with the dm_session_lock spinlock held. But create_proc_entry() calls kmalloc(GFP_KERNEL), which can sleep, so this isn't safe.

We have observed this to cause deadlocks with multiple processes creating/using DMAPI sessions concurrently (this was with SLES10's 2.6.16.21-0.8 kernel, but the DMAPI code in question is the same in CVS HEAD):

BUG: spinlock cpu recursion on CPU#1, a1/3235

lock: f930c49c, .magic: dead4ead, .owner: a2/22546, .owner_cpu: 1

Stack traceback for pid 6144
0xdfc98270 6144 2748 1 0 R 0xdfc98450 a1
EBP EIP Function (args)
0xf0f5be24 0xc010d89f delay_tsc+0xc (0xf0f5be44) 0xf0f5be2c 0xc01cd928 __delay+0xc (0x1, 0x18, 0xf0f5be90, 0xf0f5be8c)

          0xc01ceb85 _raw_spin_lock+0x79

0xf0f5be4c 0xc02afd93 _spin_lock+0x8 (0x1, 0x18, 0xf0f5be8c, 0x1) 0xf0f5be64 0xf9307302 [dmapi]dm_find_session_and_lock+0x1a (0x2220a, 0x1, 0x8fb5b198, 0x6f6b8864, 0xe)
0xf0f5bea0 0xf93062eb [dmapi]dm_app_get_tdp+0x87 (0xffffffff, 0x2, 0x1, 0xf0f5beb8, 0x3000)
0xf0f5bec0 0xf9302cf6 [dmapi]dm_read_invis_rvp+0x17 (0xffffffff, 0x27c4000, 0x0, 0x4000, 0x0)
0xf0f5bf48 0xf93014b9 [dmapi]dmapi_ioctl+0x4ab (0xab0be160, 0x28, 0xfffffff7, 0xf787f9c0, 0xab0be160)
0xf0f5bf64 0xc01700d3 do_ioctl+0x4f (0xaf345000, 0xf6f58240, 0x1b, 0x2, 0xaf3459ac)
0xf0f5bf98 0xc0170346 vfs_ioctl+0x25a (0xab0be160, 0x1, 0x1b, 0x0, 0xb7825bf0)
0xf0f5bfb4 0xc01703a9 sys_ioctl+0x50

          0xc0103d1b sysenter_past_esp+0x54

Stack traceback for pid 3254
0xdfec0720 3254 2748 1 1 R 0xdfec0900 *a1
EBP EIP Function (args)
0xf6f71e40 0xc01ce862 spin_bug (0xf66cbf20, 0xffffffda, 0xf6f71ec0, 0xf6f71ebc)

          0xc01ceb58 _raw_spin_lock+0x4c

0xf6f71e48 0xc02afd93 _spin_lock+0x8 (0x1, 0xffffffda, 0x0, 0xb32f01d0) 0xf6f71e60 0xf9307302 [dmapi]dm_find_session_and_lock+0x1a (0x0, 0x1, 0x0, 0x0, 0x3)
0xf6f71ed0 0xf9307538 [dmapi]dm_get_events+0x24 (0xfff, 0xad2e2ae8, 0xb32f02c8, 0x1, 0x0)
0xf6f71f48 0xf9301274 [dmapi]dmapi_ioctl+0x266 (0xb32f01d0, 0x12, 0xfffffff7, 0xf787f9c0, 0xb32f01d0)
0xf6f71f64 0xc01700d3 do_ioctl+0x4f (0x0, 0x0, 0x1b, 0xf66d31cc, 0x8517980)
0xf6f71f98 0xc0170346 vfs_ioctl+0x25a (0xb32f01d0, 0x1, 0x1b, 0xad2f7400, 0xb32f02c4)
0xf6f71fb4 0xc01703a9 sys_ioctl+0x50

          0xc0103d1b sysenter_past_esp+0x54

Stack traceback for pid 12452
0xdfb047e0 12452 12451 0 1 R 0xdfb049c0 a2
EBP EIP Function (args)
0xf14cbcbc 0xc02ae254 schedule+0xb84 (0xdffff180)
0xf14cbcc8 0xc02ae33b cond_resched+0x36 (0x0, 0x1, 0xf14cbe53) 0xf14cbcdc 0xc015d07a __kmalloc+0x4a (0x1, 0x8124, 0xa, 0x8, 0xf14cbe48) 0xf14cbd04 0xc018ef93 proc_create+0x8c (0x1, 0xf784d440, 0xf14cbe34, 0xd53b5de8)
0xf14cbd1c 0xc018f045 create_proc_entry+0x5f (0xf14cbe34, 0xf9309030, 0xd53b5de8, 0x7, 0x61637942)
0xf14cbedc 0xf9307c14 [dmapi]dm_create_session+0x234 (0x0, 0x0, 0x80db388, 0xb7fccff4, 0x82fa604)
0xf14cbf48 0xf93010b0 [dmapi]dmapi_ioctl+0xa2 (0xbfd1fb00, 0x3, 0xfffffff7, 0xf1399540, 0xbfd1fb00)
0xf14cbf64 0xc01700d3 do_ioctl+0x4f (0xf54cf080, 0xf782cee4, 0x3, 0xc02b0c16, 0x0)
0xf14cbf98 0xc0170346 vfs_ioctl+0x25a (0xbfd1fb00, 0x0, 0x3, 0x82fa600, 0x2)
0xf14cbfb4 0xc01703a9 sys_ioctl+0x50

          0xc0103d1b sysenter_past_esp+0x54

It doesn't appear necessary for create/remove_proc_entry() to be called with the dm_session_lock spinlock held. The following patch moves these calls outside of the spinlock.

Signed-off-by Kevin Jamieson <[email protected]>

Index: fs/dmapi/dmapi_session.c
===================================================================
RCS file: /cvs/linux-2.6-xfs/fs/dmapi/dmapi_session.c,v retrieving revision 1.31
diff -u -r1.31 dmapi_session.c

dmapi/dmapi_session.c 16 Feb 2007 06:14:08 -0000 renamed from dmapi/dmapi_session.c 12 Jan 2007 15:07:58 -0000 1.31 +10 -9

@@ -519,13 +519,14 @@
        sv_init(&s->sn_readerq, SV_DEFAULT, "dmreadq");
        sv_init(&s->sn_writerq, SV_DEFAULT, "dmwritq");
        spinlock_init(&s->sn_qlock, "sn_qlock");
-        lc = mutex_spinlock(&dm_session_lock);
    } else {
        lc = mutex_spinlock(&dm_session_lock);
        if ((error = dm_find_session(old, &s)) != 0) {
            mutex_spinunlock(&dm_session_lock, lc);
            return(error);
        }
+        unlink_session(s);
+        mutex_spinunlock(&dm_session_lock, lc);
 #ifdef CONFIG_PROC_FS
        {
        char buf[100];

@@ -533,12 +534,13 @@
        remove_proc_entry(buf, NULL);
        }
 #endif
-        unlink_session(s);
    }
    memcpy(s->sn_info, sessinfo, len);
    s->sn_info[len-1] = 0;        /* if not NULL, then now 'tis */
    s->sn_sessid = sid;
+    lc = mutex_spinlock(&dm_session_lock);
    link_session(s);
+    mutex_spinunlock(&dm_session_lock, lc);
 #ifdef CONFIG_PROC_FS
    {
    char buf[100];

@@ -549,7 +551,6 @@
    entry->owner = THIS_MODULE;
    }
 #endif
-    mutex_spinunlock(&dm_session_lock, lc);
    return(0);
 }
 

@@ -583,6 +584,12 @@
        mutex_spinunlock(&dm_session_lock, lc);
        return(-EBUSY);
    }
+   
+    /* The session is not in use.  Dequeue it from the session chain. */
+
+    unlink_session(s);
+    nested_spinunlock(&s->sn_qlock);
+    mutex_spinunlock(&dm_session_lock, lc);
 
 #ifdef CONFIG_PROC_FS
    {

@@ -592,12 +599,6 @@
    }
 #endif
 
-    /* The session is not in use.  Dequeue it from the session chain. */
-
-    unlink_session(s);
-    nested_spinunlock(&s->sn_qlock);
-    mutex_spinunlock(&dm_session_lock, lc);
-
    /* Now clear the sessions's disposition registration, and then 

destroy
the session structure.
*/