Re: [PATCH v5 0/4] [SCSI] sg: fix race condition in sg_open

From: Douglas Gilbert
Date: Sat Aug 03 2013 - 01:26:18 EST

On 13-08-01 01:01 AM, Douglas Gilbert wrote:
On 13-07-22 01:03 PM, JÃrn Engel wrote:
On Mon, 22 July 2013 12:40:29 +0800, Vaughan Cao wrote:

There is a race when open sg with O_EXCL flag. Also a race may happen between
sg_open and sg_remove.

Changes from v4:
* [3/4] use ERR_PTR series instead of adding another parameter in sg_add_sfp
* [4/4] fix conflict for cherry-pick from v3.

Changes from v3:
* release o_sem in sg_release(), not in sg_remove_sfp().
* not set exclude with sfd_lock held.

Vaughan Cao (4):
[SCSI] sg: use rwsem to solve race during exclusive open
[SCSI] sg: no need sg_open_exclusive_lock
[SCSI] sg: checking sdp->detached isn't protected when open
[SCSI] sg: push file descriptor list locking down to per-device

drivers/scsi/sg.c | 178 +++++++++++++++++++++++++-----------------------------
1 file changed, 83 insertions(+), 95 deletions(-)

Patchset looks good to me, although I didn't test it on hardware yet.
Signed-off-by: Joern Engel <joern@xxxxxxxxx>

James, care to pick this up?

Acked-by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>

Tested O_EXCL with multiple processes and threads; passed.
sg driver prior to this patch had "leaky" O_EXCL logic
according to the same test. Block device passed.

James, could you clean this up:
drivers/scsi/sg.c:242:6: warning: unused variable âresâ [-Wunused-variable]

Further testing suggests this patch on the sg driver is
broken, so I'll rescind my ack.

The case it is broken for is when a device is opened
without O_EXCL. Now if, while it is open, a second
thread/process tries to open the same device O_EXCL
then IMO the second open should fail with EBUSY.

My testing shows that O_EXCL opens properly deflect
other O_EXCL opens.

BTW the standard block driver (e.g. /dev/sdc) is broken
in exactly the same way, according to my tests.

Doug Gilbert

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