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
Simon-
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