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author | Sebastian Andrzej Siewior <bigeasy@linutronix.de> | 2015-09-05 01:47:50 +0300 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2015-09-05 02:54:41 +0300 |
commit | ce9ce6659a5775047ad529ed77ab119da5fb8b0c (patch) | |
tree | 84a687f172c8f05e33282567048ae024207c1bae /sound/firewire/lib.c | |
parent | c98c36355dd6d5c4433c8d17e8eb839ca9b97606 (diff) | |
download | linux-ce9ce6659a5775047ad529ed77ab119da5fb8b0c.tar.xz |
mm: memcontrol: bring back the VM_BUG_ON() in mem_cgroup_swapout()
Clark stumbled over a VM_BUG_ON() in -RT which was then was removed by
Johannes in commit f371763a79d ("mm: memcontrol: fix false-positive
VM_BUG_ON() on -rt"). The comment before that patch was a tiny bit better
than it is now. While the patch claimed to fix a false-postive on -RT
this was not the case. None of the -RT folks ACKed it and it was not a
false positive report. That was a *real* problem.
This patch updates the comment that is improper because it refers to
"disabled preemption" as a consequence of that lock being taken. A
spin_lock() disables preemption, true, but in this case the code relies on
the fact that the lock _also_ disables interrupts once it is acquired.
And this is the important detail (which was checked the VM_BUG_ON()) which
needs to be pointed out. This is the hint one needs while looking at the
code. It was explained by Johannes on the list that the per-CPU variables
are protected by local_irq_save(). The BUG_ON() was helpful. This code
has been workarounded in -RT in the meantime. I wouldn't mind running
into more of those if the code in question uses *special* kind of locking
since now there is no verification (in terms of lockdep or BUG_ON()) and
therefore I bring the VM_BUG_ON() check back in.
The two functions after the comment could also have a "local_irq_save()"
dance around them in order to serialize access to the per-CPU variables.
This has been avoided because the interrupts should be off.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Clark Williams <williams@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'sound/firewire/lib.c')
0 files changed, 0 insertions, 0 deletions