Messages in this thread | | | Subject | Re: [PATCH] ses: Fix racy cleanup of /sys in remove_dev() | From | Calvin Owens <> | Date | Wed, 27 Jul 2016 18:04:12 -0700 |
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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 <calvinowens@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, >>> >>
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