Re: [PATCH v2 1/1] [SCSI] sg: fix race condition when do exclusiveopen

From: vaughan
Date: Thu Jul 04 2013 - 21:57:49 EST

On 06/26/2013 09:37 AM, vaughan wrote:
Hi JÃrn Engel,

Ping.
How about this one? I found my lat patch hasn't fix the issue, so I
modified it a little more. Last thread is:
Subject: Re: [PATCH] sg: atomize check and set sdp->exclude in sg_open
Message-ID: <20130605154106.GA2737@xxxxxxxxx>

Regards,
Vaughan

ä 2013å06æ17æ 21:10, vaughan åé:
Rewrite the last patch.
Add a new field 'toopen' in sg_device to count ongoing sg_open's. By checking both 'toopen' and 'exclude' marks when do exclusive open, old race conditions can be avoided.
Replace global sg_open_exclusive_lock with a per device lock - sfd_lock. Since sfds list is now protected by the lock owned by the same sg_device, sg_index_lock becomes a real global lock to only protect sg devices lookup.
Also did some cleanup, such as remove get_exclude() and rename set_exclude() to clear_exclude().

Signed-off-by: Vaughan Cao <vaughan.cao@xxxxxxxxxx>
---
drivers/scsi/sg.c | 152 ++++++++++++++++++++++++++++++++----------------------
1 file changed, 90 insertions(+), 62 deletions(-)

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 25b5455..b0ea73f 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -103,11 +103,8 @@ static int scatter_elem_sz_prev = SG_SCATTER_SZ;
static int sg_add(struct device *, struct class_interface *);
static void sg_remove(struct device *, struct class_interface *);

-static DEFINE_SPINLOCK(sg_open_exclusive_lock);
-
static DEFINE_IDR(sg_index_idr);
-static DEFINE_RWLOCK(sg_index_lock); /* Also used to lock
- file descriptor list for device */
+static DEFINE_RWLOCK(sg_index_lock); /* protect sg index */

static struct class_interface sg_interface = {
.add_dev = sg_add,
@@ -144,7 +141,7 @@ typedef struct sg_request { /* SG_MAX_QUEUE requests outstanding per file */
} Sg_request;

typedef struct sg_fd { /* holds the state of a file descriptor */
- /* sfd_siblings is protected by sg_index_lock */
+ /* sfd_siblings is protected by sfd_lock of sg_device */
struct list_head sfd_siblings;
struct sg_device *parentdp; /* owning device */
wait_queue_head_t read_wait; /* queue read until command done */
@@ -171,10 +168,10 @@ typedef struct sg_device { /* holds the state of each scsi generic 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 */
+ spinlock_t sfd_lock; /* protect sfds, exclude, toopen */
struct list_head sfds;
+ int toopen; /* number of who are ready to open sg */
volatile char detached; /* 0->attached, 1->detached pending removal */
- /* exclude protected by sg_open_exclusive_lock */
char exclude; /* opened for exclusive access */
char sgdebug; /* 0->off, 1->sense, 9->dump dev, 10-> all devs */
struct gendisk *disk;
@@ -224,25 +221,44 @@ static int sg_allow_access(struct file *filp, unsigned char *cmd)
return blk_verify_command(q, cmd, filp->f_mode & FMODE_WRITE);
}

-static int get_exclude(Sg_device *sdp)
+static void clear_exclude(Sg_device *sdp)
{
unsigned long flags;
- int ret;

- spin_lock_irqsave(&sg_open_exclusive_lock, flags);
- ret = sdp->exclude;
- spin_unlock_irqrestore(&sg_open_exclusive_lock, flags);
+ spin_lock_irqsave(&sdp->sfd_lock, flags);
+ sdp->exclude = 0;
+ spin_unlock_irqrestore(&sdp->sfd_lock, flags);
+ return;
+}
+
+/* we can add exclusively only when no other addition is going on */
+static int try_add_exclude(Sg_device *sdp)
+{
+ unsigned long flags;
+ int ret = 0;
+
+ spin_lock_irqsave(&sdp->sfd_lock, flags);
+ if (list_empty(&sdp->sfds) && !sdp->toopen) {
+ sdp->exclude = 1;
+ sdp->toopen++;
+ ret = 1;
+ }
+ spin_unlock_irqrestore(&sdp->sfd_lock, flags);
return ret;
}

-static int set_exclude(Sg_device *sdp, char val)
+static int try_add_shareable(Sg_device *sdp)
{
unsigned long flags;
+ int ret = 0;

- spin_lock_irqsave(&sg_open_exclusive_lock, flags);
- sdp->exclude = val;
- spin_unlock_irqrestore(&sg_open_exclusive_lock, flags);
- return val;
+ spin_lock_irqsave(&sdp->sfd_lock, flags);
+ if (!sdp->exclude && sdp->toopen != INT_MAX) {
+ sdp->toopen++;
+ ret = 1;
+ }
+ spin_unlock_irqrestore(&sdp->sfd_lock, flags);
+ return ret;
}

static int sfds_list_empty(Sg_device *sdp)
@@ -250,9 +266,9 @@ static int sfds_list_empty(Sg_device *sdp)
unsigned long flags;
int ret;

- read_lock_irqsave(&sg_index_lock, flags);
+ spin_lock_irqsave(&sdp->sfd_lock, flags);
ret = list_empty(&sdp->sfds);
- read_unlock_irqrestore(&sg_index_lock, flags);
+ spin_unlock_irqrestore(&sdp->sfd_lock, flags);
return ret;
}

@@ -266,6 +282,7 @@ sg_open(struct inode *inode, struct file *filp)
Sg_fd *sfp;
int res;
int retval;
+ unsigned long iflags;

nonseekable_open(inode, filp);
SCSI_LOG_TIMEOUT(3, printk("sg_open: dev=%d, flags=0x%x\n", dev, flags));
@@ -293,27 +310,26 @@ sg_open(struct inode *inode, struct file *filp)
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) {
+ 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)
+ res = try_add_exclude(sdp);
+ else
+ res = try_add_shareable(sdp);
+ if (!res) {
retval = -EBUSY;
goto error_out;
}
- res = wait_event_interruptible(sdp->o_excl_wait, !get_exclude(sdp));
+ } else {
+ if (flags & O_EXCL)
+ res = wait_event_interruptible(sdp->o_excl_wait,
+ try_add_exclude(sdp));
+ else
+ res = wait_event_interruptible(sdp->o_excl_wait,
+ try_add_shareable(sdp));
if (res) {
retval = res; /* -ERESTARTSYS because signal hit process */
goto error_out;
@@ -331,10 +347,12 @@ sg_open(struct inode *inode, struct file *filp)
if ((sfp = sg_add_sfp(sdp, dev)))
filp->private_data = sfp;
else {
- if (flags & O_EXCL) {
- set_exclude(sdp, 0); /* undo if error */
- wake_up_interruptible(&sdp->o_excl_wait);
- }
+ spin_lock_irqsave(&sdp->sfd_lock, iflags);
+ sdp->toopen--;
+ if (flags & O_EXCL)
+ sdp->exclude = 0; /* undo if error */
+ spin_unlock_irqrestore(&sdp->sfd_lock, iflags);
+ wake_up_interruptible(&sdp->o_excl_wait);
retval = -ENOMEM;
goto error_out;
}
@@ -362,7 +380,7 @@ sg_release(struct inode *inode, struct file *filp)
return -ENXIO;
SCSI_LOG_TIMEOUT(3, printk("sg_release: %s\n", sdp->disk->disk_name));

- set_exclude(sdp, 0);
+ clear_exclude(sdp);
wake_up_interruptible(&sdp->o_excl_wait);

scsi_autopm_put_device(sdp->device);
@@ -1414,6 +1432,7 @@ static Sg_device *sg_alloc(struct gendisk *disk, struct scsi_device *scsidp)
disk->first_minor = k;
sdp->disk = disk;
sdp->device = scsidp;
+ spin_lock_init(&sdp->sfd_lock);
INIT_LIST_HEAD(&sdp->sfds);
init_waitqueue_head(&sdp->o_excl_wait);
sdp->sg_tablesize = queue_max_segments(q);
@@ -1557,10 +1576,12 @@ static void sg_remove(struct device *cl_dev, struct class_interface *cl_intf)
/* Need a write lock to set sdp->detached. */
write_lock_irqsave(&sg_index_lock, iflags);
sdp->detached = 1;
+ spin_lock(&sdp->sfd_lock);
list_for_each_entry(sfp, &sdp->sfds, sfd_siblings) {
wake_up_interruptible(&sfp->read_wait);
kill_fasync(&sfp->async_qp, SIGPOLL, POLL_HUP);
}
+ spin_unlock(&sdp->sfd_lock);
write_unlock_irqrestore(&sg_index_lock, iflags);

sysfs_remove_link(&scsidp->sdev_gendev.kobj, "generic");
@@ -2085,9 +2106,12 @@ sg_add_sfp(Sg_device * sdp, int dev)
sfp->cmd_q = SG_DEF_COMMAND_Q;
sfp->keep_orphan = SG_DEF_KEEP_ORPHAN;
sfp->parentdp = sdp;
- write_lock_irqsave(&sg_index_lock, iflags);
+ spin_lock_irqsave(&sdp->sfd_lock, iflags);
list_add_tail(&sfp->sfd_siblings, &sdp->sfds);
- write_unlock_irqrestore(&sg_index_lock, iflags);
+ sdp->toopen--; /* ongoing open is complete */
+ if (sdp->toopen == INT_MAX-1)
+ wake_up_interruptible(&sdp->o_excl_wait);
+ spin_unlock_irqrestore(&sdp->sfd_lock, iflags);
SCSI_LOG_TIMEOUT(3, printk("sg_add_sfp: sfp=0x%p\n", sfp));
if (unlikely(sg_big_buff != def_reserved_size))
sg_big_buff = def_reserved_size;
@@ -2137,9 +2161,9 @@ static void sg_remove_sfp(struct kref *kref)
struct sg_device *sdp = sfp->parentdp;
unsigned long iflags;

- write_lock_irqsave(&sg_index_lock, iflags);
+ spin_lock_irqsave(&sdp->sfd_lock, iflags);
list_del(&sfp->sfd_siblings);
- write_unlock_irqrestore(&sg_index_lock, iflags);
+ spin_unlock_irqrestore(&sdp->sfd_lock, iflags);
wake_up_interruptible(&sdp->o_excl_wait);

INIT_WORK(&sfp->ew.work, sg_remove_sfp_usercontext);
@@ -2531,7 +2555,7 @@ static int sg_proc_seq_show_devstrs(struct seq_file *s, void *v)
return 0;
}

-/* must be called while holding sg_index_lock */
+/* must be called while holding sg_index_lock and sfd_lock */
static void sg_proc_debug_helper(struct seq_file *s, Sg_device * sdp)
{
int k, m, new_interface, blen, usg;
@@ -2616,22 +2640,26 @@ static int sg_proc_seq_show_debug(struct seq_file *s, void *v)

read_lock_irqsave(&sg_index_lock, iflags);
sdp = it ? sg_lookup_dev(it->index) : NULL;
- if (sdp && !list_empty(&sdp->sfds)) {
- struct scsi_device *scsidp = sdp->device;
+ if (sdp) {
+ spin_lock(&sdp->sfd_lock);
+ if (!list_empty(&sdp->sfds)) {
+ struct scsi_device *scsidp = sdp->device;

- seq_printf(s, " >>> device=%s ", sdp->disk->disk_name);
- if (sdp->detached)
- seq_printf(s, "detached pending close ");
- else
- seq_printf
- (s, "scsi%d chan=%d id=%d lun=%d em=%d",
- scsidp->host->host_no,
- scsidp->channel, scsidp->id,
- scsidp->lun,
- scsidp->host->hostt->emulated);
- seq_printf(s, " sg_tablesize=%d excl=%d\n",
- sdp->sg_tablesize, get_exclude(sdp));
- sg_proc_debug_helper(s, sdp);
+ seq_printf(s, " >>> device=%s ", sdp->disk->disk_name);
+ if (sdp->detached)
+ seq_printf(s, "detached pending close ");
+ else
+ seq_printf
+ (s, "scsi%d chan=%d id=%d lun=%d em=%d",
+ scsidp->host->host_no,
+ scsidp->channel, scsidp->id,
+ scsidp->lun,
+ scsidp->host->hostt->emulated);
+ seq_printf(s, " sg_tablesize=%d excl=%d\n",
+ sdp->sg_tablesize, sdp->exclude);
+ sg_proc_debug_helper(s, sdp);
+ }
+ spin_unlock(&sdp->sfd_lock);
}
read_unlock_irqrestore(&sg_index_lock, iflags);
return 0;


Ping. Hope you're back.
I've tested it with many combinations of exclusive and shared opens.

Regards,
Vaughan
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