On 06/15/2016 01:24 PM, Calvin Owens wrote:
On Thursday 06/02 at 15:50 -0700, Calvin Owens wrote:
On 05/13/2016 01:28 PM, Calvin Owens wrote:
Currently we free the resources backing the enclosure device before we
call device_unregister(). This is racy: during rmmod of low-level SCSI
drivers that hook into enclosure, we end up with a small window of time
during which writing to /sys can OOPS. Example trace with mpt3sas:
Ping?
Any thoughts? Squinting at this more it still seems racy, but a narrow race
is surely better than just blatantly freeing everything while the file is
still exposed in /sys? Is there a better way you'd prefer I accomplish this?
(I have boxes that OOPS all the time from monitoring code reading the /sys
files, with this patch I haven't seen a single one.)
Thanks,
Calvin
Ping? Thoughts, comments?
general protection fault: 0000 [#1] SMP KASAN
Modules linked in: mpt3sas(-) <...>
RIP: [<ffffffffa0388a98>] ses_get_page2_descriptor.isra.6+0x38/0x220 [ses]
Call Trace:
[<ffffffffa0389d14>] ses_set_fault+0xf4/0x400 [ses]
[<ffffffffa0361069>] set_component_fault+0xa9/0xf0 [enclosure]
[<ffffffff8205bffc>] dev_attr_store+0x3c/0x70
[<ffffffff81677df5>] sysfs_kf_write+0x115/0x180
[<ffffffff81675725>] kernfs_fop_write+0x275/0x3a0
[<ffffffff8151f810>] __vfs_write+0xe0/0x3e0
[<ffffffff8152281f>] vfs_write+0x13f/0x4a0
[<ffffffff81526731>] SyS_write+0x111/0x230
[<ffffffff828b401b>] entry_SYSCALL_64_fastpath+0x13/0x94
Fortunately the solution is extremely simple: call device_unregister()
before we free the resources, and the race no longer exists. The driver
core holds a reference over ->remove_dev(), so AFAICT this is safe.
Signed-off-by: Calvin Owens <calvinow...@fb.com>
---
drivers/scsi/ses.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/scsi/ses.c b/drivers/scsi/ses.c
index 53ef1cb..0e8601a 100644
--- a/drivers/scsi/ses.c
+++ b/drivers/scsi/ses.c
@@ -778,6 +778,8 @@ static void ses_intf_remove_enclosure(struct scsi_device
*sdev)
if (!edev)
return;
+ enclosure_unregister(edev);
+
ses_dev = edev->scratch;
edev->scratch = NULL;
@@ -789,7 +791,6 @@ static void ses_intf_remove_enclosure(struct scsi_device
*sdev)
kfree(edev->component[0].scratch);
put_device(&edev->edev);
- enclosure_unregister(edev);
}
static void ses_intf_remove(struct device *cdev,
