Re: [PATCH v5 0/4] [SCSI] sg: fix race condition in sg_open
From: Douglas Gilbert
Date: Tue Aug 27 2013 - 09:15:23 EST
On 13-08-27 10:16 AM, vaughan wrote:
On 08/13/2013 11:16 AM, Douglas Gilbert wrote:
On 13-08-12 10:46 PM, vaughan wrote:
On 08/06/2013 04:52 AM, Douglas Gilbert wrote:
On 13-08-04 10:19 PM, vaughan wrote:
On 08/03/2013 01:25 PM, Douglas Gilbert wrote:
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
locking
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.
Hi Doug,
My test don't have this issue. The routine is something as below:
I start three opens without O_EXCL, wait 30s each, and open with
O_EXCL|O_NONBLOCK, it failed with EBUSY.
And I also call myopen with/without O_EXCL many times in background at
the same time, and the test is passed. I don't know why it failed in
your test.
Usage: myopen [-e][-n][-d delay] -f file
-e: exclude
-n: nonblock
-d: delay N seconds and then close.
[root@vacaowol5 16835013]# ./myopen -f /dev/sg5 -d 30 &
[1] 3417
[root@vacaowol5 16835013]# ./myopen -f /dev/sg5 -d 30 &
[2] 3418
[root@vacaowol5 16835013]# ./myopen -f /dev/sg5 -d 30 &
[3] 3419
[root@vacaowol5 16835013]# cat /proc/scsi/sg/debug
max_active_device=6(origin 1)
def_reserved_size=32768
>>> device=sg5 scsi5 chan=0 id=1 lun=0 em=0 sg_tablesize=55
excl=0
FD(1): timeout=60000ms bufflen=32768 (res)sgat=1 low_dma=0
cmd_q=0 f_packid=0 k_orphan=0 closed=0
No requests active
FD(2): timeout=60000ms bufflen=32768 (res)sgat=1 low_dma=0
cmd_q=0 f_packid=0 k_orphan=0 closed=0
No requests active
FD(3): timeout=60000ms bufflen=32768 (res)sgat=1 low_dma=0
cmd_q=0 f_packid=0 k_orphan=0 closed=0
No requests active
[root@vacaowol5 16835013]# ./myopen -e -n -f /dev/sg5 -d 30 &
[4] 3422
[3422:3351] /dev/sg5:exclude: Device or resource busy
[4]+ Exit 1 ./myopen -e -n -f /dev/sg5 -d 30
[root@vacaowol5 16835013]# cat /proc/scsi/sg/debug
max_active_device=6(origin 1)
def_reserved_size=32768
>>> device=sg5 scsi5 chan=0 id=1 lun=0 em=0 sg_tablesize=55
excl=0
FD(1): timeout=60000ms bufflen=32768 (res)sgat=1 low_dma=0
cmd_q=0 f_packid=0 k_orphan=0 closed=0
No requests active
FD(2): timeout=60000ms bufflen=32768 (res)sgat=1 low_dma=0
cmd_q=0 f_packid=0 k_orphan=0 closed=0
No requests active
FD(3): timeout=60000ms bufflen=32768 (res)sgat=1 low_dma=0
cmd_q=0 f_packid=0 k_orphan=0 closed=0
No requests active
[root@vacaowol5 16835013]# cat /proc/scsi/sg/debug
[1] Done ./myopen -f /dev/sg5 -d 30
[2]- Done ./myopen -f /dev/sg5 -d 30
[3]+ Done ./myopen -f /dev/sg5 -d 30
Hi,
After the initial failures about 36 hours ago, retesting
yesterday and today has not produced any unexpected
failures. And I have been trying hard on lk 3.10.4 and
lk 3.10.5 .
My test program is a bit more intense than yours and can
be found in the sg3_utils beta in the News section of this
page:
http://sg.danny.cz/sg/
It is in the examples directory, two variants called
sg_tst_excl and sg_tst_excl2 . You will need a recent gcc
compiler, IOW something that can compile c++11 . gcc 4.7.3
in Ubuntu 13.04 only just manages, fedora 19 should do
better with gcc 4.8.1 . The threading is implemented using
pthreads so it should be reliable.
Typically I run multiple instances (processes) and each has
multiple threads. One instance can run '-x' which will cause
its first thread not to use O_EXCL **. All my tests currently
use O_NONBLOCK and that leads to lots of EBUSYs (sometimes
in the billions).
Doug Gilbert
** Using '-x' on two instances will cause an expected failure
so can be used as a control.
Hi Doug,
Can I regard this as you ACK it again?
Hi,
I'd like you to test your setup with sg_tst_excl or sg_tst_excl2 .
Since my last email, I have not seen any more failures with those
tests on the patched sg driver but I did see a couple on
/dev/sd* . With sg_tst_excl2, bsg devices can be used and since bsg
accepts and ignores O_EXCL, it fails reliably.
BTW I use scsi_debug with 'delay=0' for a pseudo device.
Doug Gilbert
Hi Doug,
I run test for sg and sd drivers with both sg_tst_excl and sg_tst_excl2
on kernel vanilla 3.10.9 with mypatches included on Fedora19 x86_64
baremachine.
* I've tried several times with different -w and -n setting, no failure
for sg driver found.
* It's easy to find failure on both patched and non-patched kernel for
sd driver with the following test command:
./sg_tst_excl -w 3 -n 2000 -t 16 -x $1 &
./sg_tst_excl -w 3 -n 2000 -t 16 $1 &
./sg_tst_excl -w 0 -n 2000 -t 16 $1 &
./sg_tst_excl -w -1 -n 2000 -t 16 $1 &
./sg_tst_excl -w -2 -n 2000 -t 16 $1 &
I think option '-w 0/-1/-2' is significant to trigger the failure, since
when I only use '-w >0', test usually passed.
Hi,
Thanks for testing that. For others trying to follow this,
the usage message for that test utility is:
Usage: sg_tst_excl [-b] [-l <lba>] [-n <n_per_thr>] [-t <num_thrs>]
[-V] [-w <wait_ms>] [-x] <disk_device>
where
-b block on open (def: O_NONBLOCK)
-l <lba> logical block to increment (def: 1000)
-n <n_per_thr> number of loops per thread (def: 200)
-t <num_thrs> number of threads (def: 4)
-V print version number then exit
-w <wait_ms> >0: sleep_for(<wait_ms>); =0: yield(); -1: no
wait; -2: sleep(0) (def: 0)
-x don't use O_EXCL on first thread (def: use
O_EXCL on all threads)
Test O_EXCL open flag with sg driver. Each open/close cycle with the
O_EXCL flag does a double increment on lba (using its first 4 bytes).
----------------------
The test is using O_EXCL as a lock so that if a 4 byte integer in
a block starts out as even (and for a scsi_debug pseudo, blocks are
zero filled) then a open,double_increment,close sequence should
always see an even number after the open. Notice that it should be
safe for one process to run with '-x' so that its first thread
opens the device without the O_EXCL flag.
Acked-by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
And I let you run with the sd driver quirk :-)
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