Currently, the *_global_[un]lock_online() routines are not at all synchronized
with CPU hotplug. Soft-lockups detected as a consequence of this race was
reported earlier at https://lkml.org/lkml/2011/8/24/185. (Thanks to Cong Meng
for finding out that the root-cause of this issue is the race condition
between br_write_[un]lock() and CPU hotplug, which results in the lock states
getting messed up).
Fixing this race by just adding {get,put}_online_cpus() at appropriate places
in *_global_[un]lock_online() is not a good option, because, then suddenly
br_write_[un]lock() would become blocking, whereas they have been kept as
non-blocking all this time, and we would want to keep them that way.
So, overall, we want to ensure 3 things:
1. br_write_lock() and br_write_unlock() must remain as non-blocking.
2. The corresponding lock and unlock of the per-cpu spinlocks must not happen
for different sets of CPUs.
3. Either prevent any new CPU online operation in between this lock-unlock, or
ensure that the newly onlined CPU does not proceed with its corresponding
per-cpu spinlock unlocked.
To achieve all this:
(a) We introduce a new spinlock that is taken by the *_global_lock_online()
routine and released by the *_global_unlock_online() routine.
(b) We register a callback for CPU hotplug notifications, and this callback
takes the same spinlock as above.
(c) We maintain a bitmap which is close to the cpu_online_mask, and once it is
initialized in the lock_init() code, all future updates to it are done in
the callback, under the above spinlock.
(d) The above bitmap is used (instead of cpu_online_mask) while locking and
unlocking the per-cpu locks.
The callback takes the spinlock upon the CPU_UP_PREPARE event. So, if the
br_write_lock-unlock sequence is in progress, the callback keeps spinning,
thus preventing the CPU online operation till the lock-unlock sequence is
complete. This takes care of requirement (3).
The bitmap that we maintain remains unmodified throughout the lock-unlock
sequence, since all updates to it are managed by the callback, which takes
the same spinlock as the one taken by the lock code and released only by the
unlock routine. Combining this with (d) above, satisfies requirement (2).
Overall, since we use a spinlock (mentioned in (a)) to prevent CPU hotplug
operations from racing with br_write_lock-unlock, requirement (1) is also
taken care of.
By the way, it is to be noted that a CPU offline operation can actually run
in parallel with our lock-unlock sequence, because our callback doesn't react
to notifications earlier than CPU_DEAD (in order to maintain our bitmap
properly). And this means, since we use our own bitmap (which is stale, on
purpose) during the lock-unlock sequence, we could end up unlocking the
per-cpu lock of an offline CPU (because we had locked it earlier, when the
CPU was online), in order to satisfy requirement (2). But this is harmless,
though it looks a bit awkward.
Debugged-by: Cong Meng <mc@linux.vnet.ibm.com>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@vger.kernel.org
* 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: time/clocksource: Fix kernel-doc warnings rtc: m41t80: Workaround broken alarm functionality rtc: Expire alarms after the time is set.
Fix various KernelDoc build warnings. Signed-off-by: Kusanagi Kouichi <slash@ac.auone-net.jp> Cc: John Stultz <johnstul@us.ibm.com> Link: http://lkml.kernel.org/r/20111219091320.0D5AF6FC03D@msa105.auone-net.jp Signed-off-by: Ingo Molnar <mingo@elte.hu>
* 'drm-intel-fixes' of git://people.freedesktop.org/~keithp/linux: drm/i915/dp: Dither down to 6bpc if it makes the mode fit drm/i915: enable semaphores on per-device defaults drm/i915: don't set unpin_work if vblank_get fails drm/i915: By default, enable RC6 on IVB and SNB when reasonable iommu: Export intel_iommu_enabled to signal when iommu is in use drm/i915/sdvo: Include LVDS panels for the IS_DIGITAL check drm/i915: prevent division by zero when asking for chipset power drm/i915: add PCH info to i915_capabilities drm/i915: set the right SDVO transcoder for CPT drm/i915: no-lvds quirk for ASUS AT5NM10T-I drm/i915: Treat pre-gen4 backlight duty cycle value consistently drm/i915: Hook up Ivybridge eDP drm/i915: add multi-threaded forcewake support
* 'for-linus' of git://git.kernel.dk/linux-block: block: don't kick empty queue in blk_drain_queue() block/swim3: Locking fixes loop: Fix discard_alignment default setting cfq-iosched: fix cfq_cic_link() race confition cfq-iosched: free cic_index if blkio_alloc_blkg_stats fails cciss: fix flush cache transfer length cciss: Add IRQF_SHARED back in for the non-MSI(X) interrupt handler loop: fix loop block driver discard and encryption comment block: initialize request_queue's numa node during
In i915 driver, we do not enable either rc6 or semaphores on SNB when dmar is enabled. The new 'intel_iommu_enabled' variable signals when the iommu code is in operation. Cc: Ted Phelps <phelps@gnusto.com> Cc: Peter <pab1612@gmail.com> Cc: Lukas Hejtmanek <xhejtman@fi.muni.cz> Cc: Andrew Lutomirski <luto@mit.edu> CC: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Eugeni Dodonov <eugeni.dodonov@intel.com> Signed-off-by: Keith Packard <keithp@keithp.com>
Exactly like roundup_pow_of_two(1), the rounddown version was buggy for
the case of a compile-time constant '1' argument. Probably because it
originated from the same code, sharing history with the roundup version
from before the bugfix (for that one, see commit 1a06a52ee1b0: "Fix
roundup_pow_of_two(1)").
However, unlike the roundup version, the fix for rounddown is to just
remove the broken special case entirely. It's simply not needed - the
generic code
1UL << ilog2(n)
does the right thing for the constant '1' argment too. The only reason
roundup needed that special case was because rounding up does so by
subtracting one from the argument (and then adding one to the result)
causing the obvious problems with "ilog2(0)".
But rounddown doesn't do any of that, since ilog2() naturally truncates
(ie "rounds down") to the right rounded down value. And without the
ilog2(0) case, there's no reason for the special case that had the wrong
value.
tl;dr: rounddown_pow_of_two(1) should be 1, not 0.
Acked-by: Dmitry Torokhov <dtor@vmware.com>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/cjb/mmc: mmc: core: Fix deadlock when the CONFIG_MMC_UNSAFE_RESUME is not defined mmc: sdhci-s3c: Remove old and misprototyped suspend operations mmc: tmio: fix clock gating on platforms with a .set_pwr() method mmc: sh_mmcif: fix clock gating on platforms with a .down_pwr() method mmc: core: Fix typo at mmc_card_sleep mmc: core: Fix power_off_notify during suspend mmc: core: Fix setting power notify state variable for non-eMMC mmc: core: Add quirk for long data read time mmc: Add module.h include to sdhci-cns3xxx.c mmc: mxcmmc: fix falling back to PIO mmc: omap_hsmmc: DMA unmap only once in case of MMC error
Adds a quirk that sets the data read timeout to a fixed value instead of relying on the information in the CSD. The timeout value chosen is 300ms since that has proven enough for the problematic cards found, but could be increased if other cards require this. This patch also enables this quirk for certain Micron cards known to have this problem. Signed-off-by: Stefan Nilsson XK <stefan.xk.nilsson@stericsson.com> Signed-off-by: Ulf Hansson <ulf.hansson@stericsson.com> Acked-by: Linus Walleij <linus.walleij@linaro.org> Cc: <stable@kernel.org> Signed-off-by: Chris Ball <cjb@laptop.org>
* git://git.kernel.org/pub/scm/linux/kernel/git/cmetcalf/linux-tile:
arch/tile: use new generic {enable,disable}_percpu_irq() routines
drivers/net/ethernet/tile: use skb_frag_page() API
asm-generic/unistd.h: support new process_vm_{readv,write} syscalls
arch/tile: fix double-free bug in homecache_free_pages()
arch/tile: add a few #includes and an EXPORT to catch up with kernel changes.