It is just plain unsafe to peek inside in-kernel
mutex structure and make assumptions about what kernel
does with those internal fields like owner.
Kernel is all too happy to stop doing the expected things
like tracing lock owner once you load a tainted module
like spl/zfs that is not GPL.
As such you will get instant assertion failures like this:
VERIFY3(((*(volatile typeof((&((&zo->zo_lock)->m_mutex))->owner) *)&
((&((&zo->zo_lock)->m_mutex))->owner))) ==
((void *)0)) failed (ffff88030be28500 == (null))
PANIC at zfs_onexit.c:104:zfs_onexit_destroy()
Showing stack for process 3626
CPU: 0 PID: 3626 Comm: mkfs.lustre Tainted: P OE ------------ 3.10.0-debug #1
Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
Call Trace:
dump_stack+0x19/0x1b
spl_dumpstack+0x44/0x50 [spl]
spl_panic+0xbf/0xf0 [spl]
zfs_onexit_destroy+0x17c/0x280 [zfs]
zfsdev_release+0x48/0xd0 [zfs]
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Chunwei Chen <david.chen@osnexus.com>
Reviewed-by: Gvozden Neskovic <neskovic@gmail.com>
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Closes#639Closes#632
Prevent race on accessing kmutex_t when the mutex is
embedded in a ref counted structure.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Gvozden Neskovic <neskovic@gmail.com>
Closes zfsonlinux/zfs#6401
Closes#637
This reverts commit d89616fda8 which
introduced some build failures which need to be resolved before
this can be merged.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #633
It is just plain unsafe to peek inside in-kernel
mutex structure and make assumptions about what kernel
does with those internal fields like owner.
Kernel is all too happy to stop doing the expected things
like tracing lock owner once you load a tainted module
like spl/zfs that is not GPL.
As such you will get instant assertion failures like this:
VERIFY3(((*(volatile typeof((&((&zo->zo_lock)->m_mutex))->owner) *)&
((&((&zo->zo_lock)->m_mutex))->owner))) ==
((void *)0)) failed (ffff88030be28500 == (null))
PANIC at zfs_onexit.c:104:zfs_onexit_destroy()
Showing stack for process 3626
CPU: 0 PID: 3626 Comm: mkfs.lustre Tainted: P OE ------------ 3.10.0-debug #1
Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
Call Trace:
dump_stack+0x19/0x1b
spl_dumpstack+0x44/0x50 [spl]
spl_panic+0xbf/0xf0 [spl]
zfs_onexit_destroy+0x17c/0x280 [zfs]
zfsdev_release+0x48/0xd0 [zfs]
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Closes#632Closes#633
Change SPL_FSTRANS to optionally contains PF_FSTRANS. Also, add
__spl_pf_fstrans_check for the checks specifically for PF_FSTRANS.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Closes#614
In Linux 4.11, torvalds/linux@2a1f062, signal handling related functions
were moved from sched.h into sched/signal.h.
Add configure checks to detect this and include the new file where
needed.
Reviewed-by: Chunwei Chen <david.chen@osnexus.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Closes#608
Commit f58040c0fc should have removed
this comment which is no longer relevant.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Clemens Fruhwirth <clemens@endorphin.org>
Issue #589
Add a dedicated system_delay_taskq for long delay like spa_deadman and
zpl_posix_acl_free. This will allow us to use system_taskq in the manner of
dispatch multiple tasks and call taskq_wait_outstanding.
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Closes#588
Add the TASKQID_INVALID and TASKQID_INITIAL macros and update the
taskq implementation and test cases to use them. This is solely
for the purposes of readability and introduces no functional change.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
In Linux 4.9, torvalds/linux@81243ea, group_info changed from 2d array via
->blocks to 1d array via ->gid. We change the spl cred functions accordingly.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Closes#581
Linux 4.8, starting from torvalds/linux@19c5d690e, will set owner to 1 when
read held instead of leave it NULL. So we change the condition to
`rw_owner(rwp) <= 1` in RW_READ_HELD.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Closeszfsonlinux/zfs#5233Closes#577
Remove the code that doesn't make any sense.
Reviewed-by: Brian Behlendorf <behlendorf@llnl.gov>
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Closes#569
Signed-off-by: Tom Caputi <tcaputi@datto.com>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#562
_ALIGNMENT_REQUIRED needs to be #defined in isa_defs.h in order to
port the Illumos checksum code to ZoL:
4185 add new cryptographic checksums to ZFS: SHA-512, Skein, Edon-R
OpenZFS-issue: https://www.illumos.org/issues/4185
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/45818ee
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#561
Current rw_tryupgrade does rw_exit and then rw_tryenter(RW_RWITER), and then
does rw_enter(RW_READER) if it fails. This violate the assumption that
rw_tryupgrade should be atomic and could cause extra contention or even lock
inversion.
This patch we implement a proper rw_tryupgrade. For rwsem-spinlock, we take
the spinlock to check rwsem->count and rwsem->wait_list. For normal rwsem, we
use cmpxchg on rwsem->count to change the value from single reader to single
writer.
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tim Chase <tim@chase2k.com>
Closes zfsonlinux/zfs#4692
Closes#554
GCC for MIPS only defines _LP64 when 64bit,
while no _ILP32 defined when 32bit.
Signed-off-by: YunQiang Su <syq@debian.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#558
This change was lost, somehow, in e5f9a9a. Since the arrays can be
rather large, they need to be allocated with vmem_zalloc() via dfl_alloc()
and freed with vmem_free() via dfl_free().
The new dfl_alloc() function should be used to allocate object of type
dkioc_free_list_t in order that they're allocated from vmem.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Nikolay Borisov <kernel@kyup.com>
Closes#543
To reduce mutex footprint, we detect the existence of owner in kernel mutex,
and rely on it if it exists.
Note that before Linux 3.0, mutex owner is of type thread_info. Also note
that, in Linux 3.18, the condition for owner is changed from
CONFIG_DEBUG_MUTEXES || CONFIG_SMP to
CONFIG_DEBUG_MUTEXES || CONFIG_MUTEX_SPIN_ON_OWNER
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#540
Signed-off-by: Dimitri John Ledkov <xnox@ubuntu.com>
Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#537
This implementation of rw_tryupgrade() behaves slightly differently
from its counterparts on other platforms. It drops the RW_READER lock
and then acquires the RW_WRITER lock leaving a small window where no
lock is held. On other platforms the lock is never released during
the upgrade process. This is necessary under Linux because the kernel
does not provide an upgrade function.
There are currently no callers in the ZFS code where this change in
behavior is a problem. In fact, in most cases the code is already
written such that if the upgrade fails the RW_READER lock is dropped
and the caller blocks waiting to acquire the lock as RW_WRITER.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Matthew Thode <prometheanfire@gentoo.org>
Closes zfsonlinux/zfs#4388
Closes#534
Perf profiling of dd on a zvol revealed that my system spent 3.16% of
its time in random_get_pseudo_bytes(). No SPL consumers need
cryptographic strength entropy, so we can reduce our overhead by
changing the implementation to utilize a fast PRNG.
The Linux kernel did not export a suitable PRNG function until it
exported get_random_int() in Linux 3.10. While we could implement an
autotools check so that we use it when it is available or even try to
access the symbol on older kernels where it is not exported using the
fact that it is exported on newer ones as justification, we can instead
implement our own pseudo-random data generator. For this purpose, I have
written one based on a 128-bit pseudo-random number generator proposed
in a paper by Sebastiano Vigna that itself was based on work by the late
George Marsaglia.
http://vigna.di.unimi.it/ftp/papers/xorshiftplus.pdf
Profiling the same benchmark with an earlier variant of this patch that
used a slightly different generator (roughly same number of
instructions) by the same author showed that time spent in
random_get_pseudo_bytes() dropped to 0.06%. That is a factor of 50
improvement. This particular generator algorithm is also well known to
be fast:
http://xorshift.di.unimi.it/#speed
The benchmark numbers there state that it runs at 1.12ns/64-bits or 7.14
GBps of throughput on an Intel Core i7-4770 in what is presumably a
single-threaded context. Using it in `random_get_pseudo_bytes()` in the
manner I have will probably not reach that level of performance, but it
should be fairly high and many times higher than the Linux
`get_random_bytes()` function that we use now, which runs at 16.3 MB/s
on my Intel Xeon E3-1276v3 processor when measured by using dd on
/dev/urandom.
Also, putting this generator's seed into per-CPU variables allows us to
eliminate overhead from both spin locks and CPU memory barriers, which
is NUMA friendly.
We could have alternatively modified consumers to use something like
`gethrtime() % 3` as suggested by both Matthew Ahrens and Tim Chase, but
that has a few potential problems that this approach avoids:
1. Switching to `gethrtime() % 3` in hot code paths today requires
diverging from illumos-gate and does nothing about potential future
patches from illumos-gate that call our slow `random_get_pseudo_bytes()`
in different hot code paths. Reimplementing `random_get_pseudo_bytes()`
with a per-CPU PRNG avoids both of those things entirely, which means
less work for us in the future.
2. Looking at the code that implements `gethrtime()`, I think it is
unlikely to be faster than this per-CPU PRNG implementation of
`random_get_pseudo_bytes()`. It would be best to go with something fast
now so that there is no point in revisiting this from a performance
perspective.
3. `gethrtime() % 3` can vary in behavior from system to system based on
kernel version, architecture and clock source. In comparison, this
per-CPU PRNG is about ~40 lines of code in `random_get_pseudo_bytes()`
that should behave consistently across all systems regardless of kernel
version, system architecture or machine clock source. It is unlikely
that we would ever need to revisit this per-CPU PRNG while the same
cannot be said for `gethrtime() % 3`.
4. `gethrtime()` uses CPU memory barriers and maybe atomic instructions
depending on the clock source, so replacing `random_get_pseudo_bytes()`
with `gethrtime()` in hot code paths could still require a future person
working on NUMA scalability to reimplement it anyway while this per-CPU
PRNG would not by virtue of using neither CPU memory barriers nor atomic
instructions. Note that I did not check various clock sources for the
presence of atomic instructions. There is simply too much code to read
and given the drawbacks versus this per-cpu PRNG, there is no point in
being certain.
5. I have heard of instances where poor quality pseudo-random numbers
caused problems for HPC code in ways that took more than a year to
identify and were remedied by switching to a higher quality source of
pseudo-random numbers. While filesystems are different than HPC code, I
do not think it is impossible for us to have instances where poor
quality pseudo-random numbers can cause problems. Opting for a well
studied PRNG algorithm that passes tests for statistical randomness over
changing callers to use `gethrtime() % 3` bypasses the need to think
about both whether poor quality pseudo-random numbers can cause problems
and the statistical quality of numbers from `gethrtime() % 3`.
6. `gethrtime()` calls `getrawmonotonic()`, which uses seqlocks. This is
probably not a huge issue, but anyone using kgdb would never be able to
step through a seqlock critical section, which is not a problem either
now or with the per-CPU PRNG:
https://en.wikipedia.org/wiki/Seqlock
The only downside that I can see is that this code's memory requirement
is O(N) where N is NR_CPUS, versus the current code and `gethrtime() %
3`, which are O(1), but that should not be a problem. The seeds will use
64KB of memory at the high end (i.e `NR_CPU == 4096`) and 16 bytes of
memory at the low end (i.e. `NR_CPU == 1`). In either case, we should
only use a few hundred bytes of code for text, especially since
`spl_rand_jump()` should be inlined into `spl_random_init()`, which
should be removed during early boot as part of "Freeing unused kernel
memory". In either case, the memory requirements are minuscule.
Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tim Chase <tim@chase2k.com>
Closes#372
This patch add a module parameter spl_taskq_kick. When writing non-zero value
to it, it will scan all the taskq, if a taskq contains a task pending for more
than 5 seconds, it will be forced to spawn a new thread. This is use as an
emergency recovery from deadlock, not a general solution.
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#529
I noticed that the SPL implementation of kobj_read_file is not correct
after comparing it with the userland implementation of kobj_read_file()
in zfsonlinux/zfs#4104.
Note that we no longer pass RLIM64_INFINITY with this, but our vn_rdwr
implementation did not support it anyway, so there is no difference.
Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#513
To prevent taskq_member holding tq_lock and doing linear search, thus causing
contention. We store the taskq pointer to which the thread belongs in tsd.
This way taskq_member will not need to touch tq_lock, and tsd has per slot
spinlock. So the contention should be reduced greatly.
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#500Closes#504Closes#505
The pfn_t typedef was inherited from Illumos but never directly
used by any SPL consumers. This didn't cause any issues until
the Linux 4.5 kernel introduced a typedef of the same name.
See torvalds/linux/commit/34c0fd54, this patch removes the
unused Illumos version to prevent a conflict.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Chunwei Chen <tuxoko@gmail.com>
Closes#524
In b4ad50a, we abandoned memalloc_noio_save in favor of spl_fstrans_mark
because earlier kernel with it doesn't turn off __GFP_FS. However, for newer
kernel, we would prefer PF_MEMALLOC_NOIO because it would work for allocation
in kernel which we cannot control otherwise. So in this patch, we turn on both
PF_FSTRANS and PF_MEMALLOC_NOIO in spl_fstrans_mark.
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#523
For earlier versions of the kernel with memalloc_noio_save, it only turns
off __GFP_IO but leaves __GFP_FS untouched during direct reclaim. This
would cause threads to direct reclaim into ZFS and cause deadlock.
Instead, we should stick to using spl_fstrans_mark. Since we would
explicitly turn off both __GFP_IO and __GFP_FS before allocation, it
will work on every version of the kernel.
This impacts kernel versions 3.9-3.17, see upstream kernel commit
torvalds/linux@934f307 for reference.
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tim Chase <tim@chase2k.com>
Closes#515
Issue zfsonlinux/zfs#4111
This patch provides 2 new kstats to display task queues:
/proc/spl/taskqs-all - Display all task queues
/proc/spl/taskqs - Display only "active" task queues
A task queue is considered to be "active" if it currently has active
(running) threads or if any of its pending, priority, delay or waitq
lists are not empty.
If the task queue has running threads, displays each thread function's
address (symbolically, if possibly) and its argument.
If the task queue has a non-empty list of pending, priority or delayed
task queue entries (taskq_ent_t), displays each entry's thread function
address and arguemnt.
If the task queue has any waiters, displays each waiting task's pid.
Note: This patch also updates some comments in taskq.h which referred to
"taskq_t" when they should have referred to "taskq_ent_t".
Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#491
This patch only addresses the issues identified by the style checker.
It contains no functional changes.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
The flags argument in spin_lock_irqsave is modified out side of spin_lock
context. We cannot use a shared variable like tq->tq_lock_flags for them. This
patch removes it and uses local variable for the flags.
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#506
When taskq_dispatch() calls taskq_thread_spawn() to create a new thread
for a taskq, linux lockdep warns of possible recursive locking. This is
a false positive.
One such call chain is as follows, when a taskq needs more threads:
taskq_dispatch->taskq_thread_spawn->taskq_dispatch
The initial taskq_dispatch() holds tq_lock on the taskq that needed more
worker threads. The later call into taskq_dispatch() takes
dynamic_taskq->tq_lock. Without subclassing, lockdep believes these
could potentially be the same lock and complains. A similar case occurs
when taskq_dispatch() then calls task_alloc().
This patch uses spin_lock_irqsave_nested() when taking tq_lock, with one
of two new lock subclasses:
subclass taskq
TQ_LOCK_DYNAMIC dynamic_taskq
TQ_LOCK_GENERAL any other
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #480
When running a kernel with CONFIG_LOCKDEP=y, lockdep reports possible
recursive locking in some cases and possible circular locking dependency
in others, within the SPL and ZFS modules.
When lockdep detects these conditions, it disables further lock analysis
for all locks. This causes /proc/lock_stats not to reflect full
information about lock contention, even in locks without dependency
issues.
This commit creates a new type of mutex, MUTEX_NOLOCKDEP. This mutex
type causes subsequent attempts to take or release those locks to be
wrapped in lockdep_off() and lockdep_on().
This commit also creates an RW_NOLOCKDEP type analagous to
MUTEX_NOLOCKDEP.
MUTEX_NOLOCKDEP and RW_NOLOCKDEP are also defined in zfs, in a commit to
that repo, for userspace builds.
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #480
The SPL fails to build with some "Configured" kernels (ex. openSUSE
xen Kernel) this change should make same binaries with C compiler
optimization.
Signed-off-by: zgock <zgock@nuc.base.zgock-lab.net>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#510
For some arm, powerpc, and sparc platforms it was possible that
neither _ILP32 of _LP64 would be defined. Update the isa_defs.h
header to explicitly set these macros and generate a compile error
in the case neither are defined.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: tuxoko <tuxoko@gmail.com>
Issue zfsonlinux/zfs#4048
This reverts commit a430c11f0b. Using
journal_info like this can cause a BUG at kernel fs/jbd2/transaction.c:425!
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #500
The ->journal_info pointer in the task_struct is reserved for use by
filesystems and because the kernel can have multiple file systems on the
same stack due to direct reclaim, each filesystem that touches
->journal_info in a callback function will save the value at the start
of its frame and restore it at the end of its frame. This allows us to
safely use ->journal_info to store a pointer to the taskq's struct in
taskq threads so that ZFS code paths can detect the presence of a taskq.
This could break if the ZFS code were to use taskq_member from the
context of direct reclaim. However, there are no such uses of it in that
manner, so this is safe.
This eliminates an O(N) list traversal under a spinlock with an O(1)
unlocked pointer comparison.
Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: tuxoko <tuxoko@gmail.com>
Signed-off-by: Tim Chase <tim@chase2k.com>
Closes#500
If a vnode is released asynchronously through areleasef(), it is
possible for the user process to reuse the file descriptor before
areleasef is called. When this happens, getf() will return a stale
reference, any operations in the kernel on that file descriptor will
fail (as it is closed) and the operations meant for that fd will
never occur from userspace's perspective.
We correct this by detecting this condition in getf(), doing a putf
on the old file handle, updating the file descriptor and proceeding
as if everything was fine. When the areleasef() is done, it will
harmlessly decrement the reference counter on the Illumos file handle.
Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#492
Replace DKIOCTRIM with DKIOCFREE and add additional support required
for Nextenta's TRIM support.
Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#469
The original P2ROUNDUP and P2ROUNDUP_TYPED macros contain -x which
triggers PaX's integer overflow detection for unsigned integers.
Replace the macros with an equivalent version that does not trigger
the overflow.
Axioms:
A. (-(x)) === (~((x) - 1)) === (~(x) + 1) under two's complement.
B. ~(x & y) === ((~(x)) | (~(y))) under De Morgan's law.
C. ~(~x) === x under the law of excluded middle.
Proof:
0. (-(-(x) & -(align))) original
1. (~(-(x) & -(align)) + 1) by A
2. (((~(-(x))) | (~(-(align)))) + 1) by B
3. (((~(~((x) - 1))) | (~(~((align) - 1)))) + 1) by A
4. (((((x) - 1)) | (((align) - 1))) + 1) by C
Q.E.D.
Signed-off-by: Jason Zaman <jason@perfinion.com>
Reviewed-by: Chris Dunlop <chris@onthe.net.au>
Reviewed-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes zfsonlinux/zfs#2505
Closes#488
Allocate a kmem cache magazine for every possible CPU which might
be added to the system. This ensures that when one of these CPUs
is enabled it can be safely used immediately.
For many systems the number of online CPUs is identical to the
number of present CPUs so this does imply an increased memory
footprint. In fact, dynamically allocating the array of magazine
pointers instead of using the worst case NR_CPUS can end up
decreasing our memory footprint.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ned Bass <bass6@llnl.gov>
Closes#482
If CONFIG_RWSEM_SPIN_ON_OWNER is defined, rw_semaphore will have an owner
field, so we don't need our own.
Signed-off-by: Chunwei Chen <tuxoko@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #473
The spin lock around rw_owner is completely unnecessary. The reason is that it
is only modified in the down_write context. If you race against another thread
modifying it, that means that you aren't holding the rwlock, so taking the
spin lock don't eliminate the race.
Also, we only check rw_owner in RW_WRITE_HELD because spl_rwsem_is_locked
is unnecessary and might need to take spin lock.
Signed-off-by: Chunwei Chen <tuxoko@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #473
