Messages in this thread | | | Date | Wed, 23 Oct 2013 10:10:47 -0400 | From | Douglas Gilbert <> | Subject | Re: [3.12-rc] sg_open: leaving the kernel with locks still held! |
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On 13-10-23 03:44 AM, James Bottomley wrote: > On Tue, 2013-10-22 at 20:41 -0400, Douglas Gilbert wrote: >> On 13-10-22 04:56 PM, Simon Kirby wrote: >>> Hello! >>> >>> While trying to figure out why the request queue to sda (ext4) was >>> clogging up on one of our btrfs backup boxes, I noticed a megarc process >>> in D state, so enabled locking debugging, and got this (on 3.12-rc6): >>> >>> [ 205.372823] ================================================ >>> [ 205.372901] [ BUG: lock held when returning to user space! ] >>> [ 205.372979] 3.12.0-rc6-hw-debug-pagealloc+ #67 Not tainted >>> [ 205.373055] ------------------------------------------------ >>> [ 205.373132] megarc.bin/5283 is leaving the kernel with locks still held! >>> [ 205.373212] 1 lock held by megarc.bin/5283: >>> [ 205.373285] #0: (&sdp->o_sem){.+.+..}, at: [<ffffffff8161e650>] sg_open+0x3a0/0x4d0 >>> >>> Vaughan, it seems you touched this area last in 15b06f9a02406e, and git >>> tag --contains says this went in for 3.12-rc. We didn't see this on 3.11, >>> though I haven't tried with lockdep. >>> >>> This is caused by some of our internal RAID monitoring scripts that run >>> "megarc.bin -dispCfg -a0" (even though that controller isn't present on >>> this server -- a PowerEdge 2950 w/Perc 5). >>> >>> strace output of the program execution that causes the above message is >>> here: http://0x.ca/sim/ref/3.12-rc6/megarc_strace.txt >> >> This has been reported. That patch will be reverted or, >> if there is enough time, a fix will (or at least should) >> go in before the release of lk 3.12 . > > I think you've got about a week to prove you can fix it (before 3.12 > goes final). I'll send my current set of fixes to Linus without doing > anything about sg.
"prove" is a big ask, especially coming from a mathematician. I consider it more hacking (in the golf sense) on my part to tweak well-meaning patches to the sg driver that cause collateral damage. Further, I suspect Vaughan's patch was an attempt to fix damage left be a previous sg_open() hacker.
I have asked Simon Kirby to apply the patch: http://marc.info/?l=linux-scsi&m=138237283432010&w=2 and report if it fixes his problems. Further I have written three test programs to test O_EXCL handling on SCSI devices, two of which are in the examples directory of sg3_utils version 1.37 . The latest one (single exclusive writer, multiple readers) can be found in the News section of: http://sg.danny.cz/sg/ These tests don't check all possibilities (e.g. random signals, ml error processing and detached devices) but they are better than nothing. And, as a side issue, they break bsg (cause it ignores O_EXCL) and break the block layer (e.g. /dev/sdb) so perhaps it should be reverted :-)
Perhaps the original bug reporter (Madper Xie) might also test the proposed patch and report if it fixes what he saw.
Doug Gilbert
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