[SCSI] Revert "sg: use rwsem to solve race during exclusive open"

This reverts commit 15b06f9a02406e5460001db6d5af5c738cd3d4e7.

This is one of four patches that was causing this bug

[  205.372823] ================================================
[  205.372901] [ BUG: lock held when returning to user space! ]
[  205.372979] 3.12.0-rc6-hw-debug-pagealloc+ #67 Not tainted
[  205.373055] ------------------------------------------------
[  205.373132] megarc.bin/5283 is leaving the kernel with locks still held!
[  205.373212] 1 lock held by megarc.bin/5283:
[  205.373285]  #0:  (&sdp->o_sem){.+.+..}, at: [<ffffffff8161e650>] sg_open+0x3a0/0x4d0

Cc: Vaughan Cao <vaughan.cao@oracle.com>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

1 files changed, 38 insertions, 41 deletions

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 4efa9b5884b7..df5e961484e1 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -170,11 +170,11 @@ typedef struct sg_fd {		/* holds the state of a file descriptor */
 
 typedef struct sg_device { /* holds the state of each scsi generic device */
         struct scsi_device *device;
+        wait_queue_head_t o_excl_wait;  /* queue open() when O_EXCL in use */
         int sg_tablesize;       /* adapter's max scatter-gather table size */
         u32 index;              /* device index number */
         /* sfds is protected by sg_index_lock */
         struct list_head sfds;
-        struct rw_semaphore o_sem;      /* exclude open should hold this rwsem */
         volatile char detached; /* 0->attached, 1->detached pending removal */
         /* exclude protected by sg_open_exclusive_lock */
         char exclude;           /* opened for exclusive access */
@@ -265,6 +265,7 @@ sg_open(struct inode *inode, struct file *filp)
         struct request_queue *q;
         Sg_device *sdp;
         Sg_fd *sfp;
+        int res;
         int retval;
 
         nonseekable_open(inode, filp);
@@ -293,35 +294,35 @@ sg_open(struct inode *inode, struct file *filp)
                 goto error_out;
         }
 
-        if ((flags & O_EXCL) && (O_RDONLY == (flags & O_ACCMODE))) {
-                retval = -EPERM; /* Can't lock it with read only access */
-                goto error_out;
-        }
-        if (flags & O_NONBLOCK) {
-                if (flags & O_EXCL) {
-                        if (!down_write_trylock(&sdp->o_sem)) {
-                                retval = -EBUSY;
-                                goto error_out;
-                        }
-                } else {
-                        if (!down_read_trylock(&sdp->o_sem)) {
-                                retval = -EBUSY;
-                                goto error_out;
-                        }
+        if (flags & O_EXCL) {
+                if (O_RDONLY == (flags & O_ACCMODE)) {
+                        retval = -EPERM; /* Can't lock it with read only access */
+                        goto error_out;
+                }
+                if (!sfds_list_empty(sdp) && (flags & O_NONBLOCK)) {
+                        retval = -EBUSY;
+                        goto error_out;
+                }
+                res = wait_event_interruptible(sdp->o_excl_wait,
+                                           ((!sfds_list_empty(sdp) || get_exclude(sdp)) ? 0 : set_exclude(sdp, 1)));
+                if (res) {
+                        retval = res;   /* -ERESTARTSYS because signal hit process */
+                        goto error_out;
+                }
+        } else if (get_exclude(sdp)) {  /* some other fd has an exclusive lock on dev */
+                if (flags & O_NONBLOCK) {
+                        retval = -EBUSY;
+                        goto error_out;
+                }
+                res = wait_event_interruptible(sdp->o_excl_wait, !get_exclude(sdp));
+                if (res) {
+                        retval = res;   /* -ERESTARTSYS because signal hit process */
+                        goto error_out;
                 }
-        } else {
-                if (flags & O_EXCL)
-                        down_write(&sdp->o_sem);
-                else
-                        down_read(&sdp->o_sem);
         }
-        /* Since write lock is held, no need to check sfd_list */
-        if (flags & O_EXCL)
-                set_exclude(sdp, 1);
-
         if (sdp->detached) {
                 retval = -ENODEV;
-                goto sem_out;
+                goto error_out;
         }
         if (sfds_list_empty(sdp)) {     /* no existing opens on this device */
                 sdp->sgdebug = 0;
@@ -330,18 +331,17 @@ sg_open(struct inode *inode, struct file *filp)
         }
         if ((sfp = sg_add_sfp(sdp, dev)))
                 filp->private_data = sfp;
-                /* retval is already provably zero at this point because of the
-                 * check after retval = scsi_autopm_get_device(sdp->device))
-                 */
         else {
-                retval = -ENOMEM;
-sem_out:
                 if (flags & O_EXCL) {
                         set_exclude(sdp, 0);    /* undo if error */
-                        up_write(&sdp->o_sem);
-                } else
-                        up_read(&sdp->o_sem);
+                        wake_up_interruptible(&sdp->o_excl_wait);
+                }
+                retval = -ENOMEM;
+                goto error_out;
+        }
+        retval = 0;
 error_out:
+        if (retval) {
                 scsi_autopm_put_device(sdp->device);
 sdp_put:
                 scsi_device_put(sdp->device);
@@ -358,18 +358,13 @@ sg_release(struct inode *inode, struct file *filp)
 {
         Sg_device *sdp;
         Sg_fd *sfp;
-        int excl;
 
         if ((!(sfp = (Sg_fd *) filp->private_data)) || (!(sdp = sfp->parentdp)))
                 return -ENXIO;
         SCSI_LOG_TIMEOUT(3, printk("sg_release: %s\n", sdp->disk->disk_name));
 
-        excl = get_exclude(sdp);
         set_exclude(sdp, 0);
-        if (excl)
-                up_write(&sdp->o_sem);
-        else
-                up_read(&sdp->o_sem);
+        wake_up_interruptible(&sdp->o_excl_wait);
 
         scsi_autopm_put_device(sdp->device);
         kref_put(&sfp->f_ref, sg_remove_sfp);
@@ -1421,7 +1416,7 @@ static Sg_device *sg_alloc(struct gendisk *disk, struct scsi_device *scsidp)
         sdp->disk = disk;
         sdp->device = scsidp;
         INIT_LIST_HEAD(&sdp->sfds);
-        init_rwsem(&sdp->o_sem);
+        init_waitqueue_head(&sdp->o_excl_wait);
         sdp->sg_tablesize = queue_max_segments(q);
         sdp->index = k;
         kref_init(&sdp->d_ref);
@@ -2132,11 +2127,13 @@ static void sg_remove_sfp_usercontext(struct work_struct *work)
 static void sg_remove_sfp(struct kref *kref)
 {
         struct sg_fd *sfp = container_of(kref, struct sg_fd, f_ref);
+        struct sg_device *sdp = sfp->parentdp;
         unsigned long iflags;
 
         write_lock_irqsave(&sg_index_lock, iflags);
         list_del(&sfp->sfd_siblings);
         write_unlock_irqrestore(&sg_index_lock, iflags);
+        wake_up_interruptible(&sdp->o_excl_wait);
 
         INIT_WORK(&sfp->ew.work, sg_remove_sfp_usercontext);
         schedule_work(&sfp->ew.work);