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Commit 065b4a2f authored by James Bottomley's avatar James Bottomley
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[SCSI] Revert "sg: use rwsem to solve race during exclusive open" 



This reverts commit 15b06f9a.

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: default avatarDouglas Gilbert <dgilbert@interlog.com>
Signed-off-by: default avatarJames Bottomley <JBottomley@Parallels.com>
parent 98481ff0

drivers/scsi/sg.c

+38 −41
Original line number Diff line number Diff line
@@ -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))) {

	if (flags & O_EXCL) {

		if (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)) {

		if (!sfds_list_empty(sdp) && (flags & O_NONBLOCK)) {

			retval = -EBUSY;

			goto error_out;

		}

		} else {

			if (!down_read_trylock(&sdp->o_sem)) {

		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);