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  1. 09 8月, 2007 2 次提交
    • P
      sched: fix bug in balance_tasks() · a4ac01c3
      由 Peter Williams 提交于 
      There are two problems with balance_tasks() and how it used:

1. The variables best_prio and best_prio_seen (inherited from the old
move_tasks()) were only required to handle problems caused by the
active/expired arrays, the order in which they were processed and the
possibility that the task with the highest priority could be on either.
  These issues are no longer present and the extra overhead associated
with their use is unnecessary (and possibly wrong).

2. In the absence of CONFIG_FAIR_GROUP_SCHED being set, the same
this_best_prio variable needs to be used by all scheduling classes or
there is a risk of moving too much load.  E.g. if the highest priority
task on this at the beginning is a fairly low priority task and the rt
class migrates a task (during its turn) then that moved task becomes the
new highest priority task on this_rq but when the sched_fair class
initializes its copy of this_best_prio it will get the priority of the
original highest priority task as, due to the run queue locks being
held, the reschedule triggered by pull_task() will not have taken place.
  This could result in inappropriate overriding of skip_for_load and
excessive load being moved.

The attached patch addresses these problems by deleting all reference to
best_prio and best_prio_seen and making this_best_prio a reference
parameter to the various functions involved.

load_balance_fair() has also been modified so that this_best_prio is
only reset (in the loop) if CONFIG_FAIR_GROUP_SCHED is set.  This should
preserve the effect of helping spread groups' higher priority tasks
around the available CPUs while improving system performance when
CONFIG_FAIR_GROUP_SCHED isn't set.
Signed-off-by: NPeter Williams <pwil3058@bigpond.net.au>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      a4ac01c3
    • P
      sched: simplify move_tasks() · 43010659
      由 Peter Williams 提交于 
      The move_tasks() function is currently multiplexed with two distinct
capabilities:

1. attempt to move a specified amount of weighted load from one run
queue to another; and
2. attempt to move a specified number of tasks from one run queue to
another.

The first of these capabilities is used in two places, load_balance()
and load_balance_idle(), and in both of these cases the return value of
move_tasks() is used purely to decide if tasks/load were moved and no
notice of the actual number of tasks moved is taken.

The second capability is used in exactly one place,
active_load_balance(), to attempt to move exactly one task and, as
before, the return value is only used as an indicator of success or failure.

This multiplexing of sched_task() was introduced, by me, as part of the
smpnice patches and was motivated by the fact that the alternative, one
function to move specified load and one to move a single task, would
have led to two functions of roughly the same complexity as the old
move_tasks() (or the new balance_tasks()).  However, the new modular
design of the new CFS scheduler allows a simpler solution to be adopted
and this patch addresses that solution by:

1. adding a new function, move_one_task(), to be used by
active_load_balance(); and
2. making move_tasks() a single purpose function that tries to move a
specified weighted load and returns 1 for success and 0 for failure.

One of the consequences of these changes is that neither move_one_task()
or the new move_tasks() care how many tasks sched_class.load_balance()
moves and this enables its interface to be simplified by returning the
amount of load moved as its result and removing the load_moved pointer
from the argument list.  This helps simplify the new move_tasks() and
slightly reduces the amount of work done in each of
sched_class.load_balance()'s implementations.

Further simplification, e.g. changes to balance_tasks(), are possible
but (slightly) complicated by the special needs of load_balance_fair()
so I've left them to a later patch (if this one gets accepted).

NB Since move_tasks() gets called with two run queue locks held even
small reductions in overhead are worthwhile.

[ mingo@elte.hu ]

this change also reduces code size nicely:

   text    data     bss     dec     hex filename
   39216    3618      24   42858    a76a sched.o.before
   39173    3618      24   42815    a73f sched.o.after
Signed-off-by: NPeter Williams <pwil3058@bigpond.net.au>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      43010659
  3. 02 8月, 2007 3 次提交
  5. 26 7月, 2007 3 次提交
    • C
      [PATCH] sched: add above_background_load() function · d02c7a8c
      由 Con Kolivas 提交于 
      Add an above_background_load() function which can be used by other
subsystems to detect if there is anything besides niced tasks running.

Place it in sched.h to allow it to be compiled out if not used.

Unused for now, but it is a useful hint to the IO scheduler and to
swap-prefetch.
Signed-off-by: NCon Kolivas <kernel@kolivas.org>
Cc: Peter Williams <pwil3058@bigpond.net.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      d02c7a8c
    • A
      [PATCH] sched: arch preempt notifier mechanism · e107be36
      由 Avi Kivity 提交于 
      This adds a general mechanism whereby a task can request the scheduler to
notify it whenever it is preempted or scheduled back in.  This allows the
task to swap any special-purpose registers like the fpu or Intel's VT
registers.
Signed-off-by: NAvi Kivity <avi@qumranet.com>
[ mingo@elte.hu: fixes, cleanups ]
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      e107be36
    • I
      [PATCH] sched: increase SCHED_LOAD_SCALE_FUZZ · b47e8608
      由 Ingo Molnar 提交于 
      increase SCHED_LOAD_SCALE_FUZZ that adds a small amount of
over-balancing: to help distribute CPU-bound tasks more fairly on SMP
systems.

the problem of unfair balancing was noticed and reported by Tong N Li.

10 CPU-bound tasks running on 8 CPUs, v2.6.23-rc1:

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 2572 mingo     20   0  1576  244  196 R  100  0.0   1:03.61 loop
 2578 mingo     20   0  1576  248  196 R  100  0.0   1:03.59 loop
 2576 mingo     20   0  1576  248  196 R  100  0.0   1:03.52 loop
 2571 mingo     20   0  1576  244  196 R  100  0.0   1:03.46 loop
 2569 mingo     20   0  1576  244  196 R   99  0.0   1:03.36 loop
 2570 mingo     20   0  1576  244  196 R   95  0.0   1:00.55 loop
 2577 mingo     20   0  1576  248  196 R   50  0.0   0:31.88 loop
 2574 mingo     20   0  1576  248  196 R   50  0.0   0:31.87 loop
 2573 mingo     20   0  1576  248  196 R   50  0.0   0:31.86 loop
 2575 mingo     20   0  1576  248  196 R   50  0.0   0:31.86 loop

v2.6.23-rc1 + patch:

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 2681 mingo     20   0  1576  244  196 R   85  0.0   3:51.68 loop
 2688 mingo     20   0  1576  244  196 R   81  0.0   3:46.35 loop
 2682 mingo     20   0  1576  244  196 R   80  0.0   3:43.68 loop
 2685 mingo     20   0  1576  248  196 R   80  0.0   3:45.97 loop
 2683 mingo     20   0  1576  248  196 R   80  0.0   3:40.25 loop
 2679 mingo     20   0  1576  244  196 R   80  0.0   3:33.53 loop
 2680 mingo     20   0  1576  244  196 R   79  0.0   3:43.53 loop
 2686 mingo     20   0  1576  244  196 R   79  0.0   3:39.31 loop
 2687 mingo     20   0  1576  244  196 R   78  0.0   3:33.31 loop
 2684 mingo     20   0  1576  244  196 R   77  0.0   3:27.52 loop

so they now nicely converge to the expected 80% long-term CPU usage.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      b47e8608
  7. 20 7月, 2007 3 次提交
  9. 17 7月, 2007 4 次提交
    • S
      user namespace: add unshare · 77ec739d
      由 Serge E. Hallyn 提交于 
      This patch enables the unshare of user namespaces.

It adds a new clone flag CLONE_NEWUSER and implements copy_user_ns() which
resets the current user_struct and adds a new root user (uid == 0)

For now, unsharing the user namespace allows a process to reset its
user_struct accounting and uid 0 in the new user namespace should be contained
using appropriate means, for instance selinux

The plan, when the full support is complete (all uid checks covered), is to
keep the original user's rights in the original namespace, and let a process
become uid 0 in the new namespace, with full capabilities to the new
namespace.
Signed-off-by: NSerge E. Hallyn <serue@us.ibm.com>
Signed-off-by: NCedric Le Goater <clg@fr.ibm.com>
Acked-by: NPavel Emelianov <xemul@openvz.org>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: Kirill Korotaev <dev@sw.ru>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: James Morris <jmorris@namei.org>
Cc: Andrew Morgan <agm@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      77ec739d
    • C
      user namespace: add the framework · acce292c
      由 Cedric Le Goater 提交于 
      Basically, it will allow a process to unshare its user_struct table,
resetting at the same time its own user_struct and all the associated
accounting.

A new root user (uid == 0) is added to the user namespace upon creation.
Such root users have full privileges and it seems that theses privileges
should be controlled through some means (process capabilities ?)

The unshare is not included in this patch.

Changes since [try #4]:
	- Updated get_user_ns and put_user_ns to accept NULL, and
	  get_user_ns to return the namespace.

Changes since [try #3]:
	- moved struct user_namespace to files user_namespace.{c,h}

Changes since [try #2]:
	- removed struct user_namespace* argument from find_user()

Changes since [try #1]:
	- removed struct user_namespace* argument from find_user()
	- added a root_user per user namespace
Signed-off-by: NCedric Le Goater <clg@fr.ibm.com>
Signed-off-by: NSerge E. Hallyn <serue@us.ibm.com>
Acked-by: NPavel Emelianov <xemul@openvz.org>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: Kirill Korotaev <dev@sw.ru>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: James Morris <jmorris@namei.org>
Cc: Andrew Morgan <agm@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      acce292c
    • M
      Audit: add TTY input auditing · 522ed776
      由 Miloslav Trmac 提交于 
      Add TTY input auditing, used to audit system administrator's actions.  This is
required by various security standards such as DCID 6/3 and PCI to provide
non-repudiation of administrator's actions and to allow a review of past
actions if the administrator seems to overstep their duties or if the system
becomes misconfigured for unknown reasons.  These requirements do not make it
necessary to audit TTY output as well.

Compared to an user-space keylogger, this approach records TTY input using the
audit subsystem, correlated with other audit events, and it is completely
transparent to the user-space application (e.g.  the console ioctls still
work).

TTY input auditing works on a higher level than auditing all system calls
within the session, which would produce an overwhelming amount of mostly
useless audit events.

Add an "audit_tty" attribute, inherited across fork ().  Data read from TTYs
by process with the attribute is sent to the audit subsystem by the kernel.
The audit netlink interface is extended to allow modifying the audit_tty
attribute, and to allow sending explanatory audit events from user-space (for
example, a shell might send an event containing the final command, after the
interactive command-line editing and history expansion is performed, which
might be difficult to decipher from the TTY input alone).

Because the "audit_tty" attribute is inherited across fork (), it would be set
e.g.  for sshd restarted within an audited session.  To prevent this, the
audit_tty attribute is cleared when a process with no open TTY file
descriptors (e.g.  after daemon startup) opens a TTY.

See https://www.redhat.com/archives/linux-audit/2007-June/msg00000.html for a
more detailed rationale document for an older version of this patch.

[akpm@linux-foundation.org: build fix]
Signed-off-by: NMiloslav Trmac <mitr@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Paul Fulghum <paulkf@microgate.com>
Cc: Casey Schaufler <casey@schaufler-ca.com>
Cc: Steve Grubb <sgrubb@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      522ed776
    • T
      Use boot based time for process start time and boot time in /proc · 924b42d5
      由 Tomas Janousek 提交于 
      Commit 411187fb caused boot time to move and
process start times to become invalid after suspend.  Using boot based time
for those restores the old behaviour and fixes the issue.

[akpm@linux-foundation.org: little cleanup]
Signed-off-by: NTomas Janousek <tjanouse@redhat.com>
Cc: Tomas Smetana <tsmetana@redhat.com>
Acked-by: NJohn Stultz <johnstul@us.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      924b42d5
  11. 10 7月, 2007 19 次提交
  13. 09 6月, 2007 1 次提交
    • A
      pi-futex: fix exit races and locking problems · 778e9a9c
      由 Alexey Kuznetsov 提交于 
      1. New entries can be added to tsk->pi_state_list after task completed
   exit_pi_state_list(). The result is memory leakage and deadlocks.

2. handle_mm_fault() is called under spinlock. The result is obvious.

3. results in self-inflicted deadlock inside glibc.
   Sometimes futex_lock_pi returns -ESRCH, when it is not expected
   and glibc enters to for(;;) sleep() to simulate deadlock. This problem
   is quite obvious and I think the patch is right. Though it looks like
   each "if" in futex_lock_pi() got some stupid special case "else if". :-)

4. sometimes futex_lock_pi() returns -EDEADLK,
   when nobody has the lock. The reason is also obvious (see comment
   in the patch), but correct fix is far beyond my comprehension.
   I guess someone already saw this, the chunk:

                        if (rt_mutex_trylock(&q.pi_state->pi_mutex))
                                ret = 0;

   is obviously from the same opera. But it does not work, because the
   rtmutex is really taken at this point: wake_futex_pi() of previous
   owner reassigned it to us. My fix works. But it looks very stupid.
   I would think about removal of shift of ownership in wake_futex_pi()
   and making all the work in context of process taking lock.

From: Thomas Gleixner <tglx@linutronix.de>

Fix 1) Avoid the tasklist lock variant of the exit race fix by adding
    an additional state transition to the exit code.

    This fixes also the issue, when a task with recursive segfaults
    is not able to release the futexes.

Fix 2) Cleanup the lookup_pi_state() failure path and solve the -ESRCH
    problem finally.

Fix 3) Solve the fixup_pi_state_owner() problem which needs to do the fixup
    in the lock protected section by using the in_atomic userspace access
    functions.

    This removes also the ugly lock drop / unqueue inside of fixup_pi_state()

Fix 4) Fix a stale lock in the error path of futex_wake_pi()

Added some error checks for verification.

The -EDEADLK problem is solved by the rtmutex fixups.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Acked-by: NIngo Molnar <mingo@elte.hu>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      778e9a9c
  15. 24 5月, 2007 2 次提交
    • R
      recalc_sigpending_tsk fixes · 7bb44ade
      由 Roland McGrath 提交于 
      Steve Hawkes discovered a problem where recalc_sigpending_tsk was called in
do_sigaction but no signal_wake_up call was made, preventing later signals
from waking up blocked threads with TIF_SIGPENDING already set.

In fact, the few other calls to recalc_sigpending_tsk outside the signals
code are also subject to this problem in other race conditions.

This change makes recalc_sigpending_tsk private to the signals code.  It
changes the outside calls, as well as do_sigaction, to use the new
recalc_sigpending_and_wake instead.
Signed-off-by: NRoland McGrath <roland@redhat.com>
Cc: <Steve.Hawkes@motorola.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      7bb44ade
    • R
      freezer: fix vfork problem · ba96a0c8
      由 Rafael J. Wysocki 提交于 
      Currently try_to_freeze_tasks() has to wait until all of the vforked processes
exit and for this reason every user can make it fail.  To fix this problem we
can introduce the additional process flag PF_FREEZER_SKIP to be used by tasks
that do not want to be counted as freezable by the freezer and want to have
TIF_FREEZE set nevertheless.  Then, this flag can be set by tasks using
sys_vfork() before they call wait_for_completion(&vfork) and cleared after
they have woken up.  After clearing it, the tasks should call try_to_freeze()
as soon as possible.
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>
Cc: Gautham R Shenoy <ego@in.ibm.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      ba96a0c8
  17. 11 5月, 2007 3 次提交
    • D
      signal/timer/event: signalfd core · fba2afaa
      由 Davide Libenzi 提交于 
      This patch series implements the new signalfd() system call.

I took part of the original Linus code (and you know how badly it can be
broken :), and I added even more breakage ;) Signals are fetched from the same
signal queue used by the process, so signalfd will compete with standard
kernel delivery in dequeue_signal().  If you want to reliably fetch signals on
the signalfd file, you need to block them with sigprocmask(SIG_BLOCK).  This
seems to be working fine on my Dual Opteron machine.  I made a quick test
program for it:

http://www.xmailserver.org/signafd-test.c

The signalfd() system call implements signal delivery into a file descriptor
receiver.  The signalfd file descriptor if created with the following API:

int signalfd(int ufd, const sigset_t *mask, size_t masksize);

The "ufd" parameter allows to change an existing signalfd sigmask, w/out going
to close/create cycle (Linus idea).  Use "ufd" == -1 if you want a brand new
signalfd file.

The "mask" allows to specify the signal mask of signals that we are interested
in.  The "masksize" parameter is the size of "mask".

The signalfd fd supports the poll(2) and read(2) system calls.  The poll(2)
will return POLLIN when signals are available to be dequeued.  As a direct
consequence of supporting the Linux poll subsystem, the signalfd fd can use
used together with epoll(2) too.

The read(2) system call will return a "struct signalfd_siginfo" structure in
the userspace supplied buffer.  The return value is the number of bytes copied
in the supplied buffer, or -1 in case of error.  The read(2) call can also
return 0, in case the sighand structure to which the signalfd was attached,
has been orphaned.  The O_NONBLOCK flag is also supported, and read(2) will
return -EAGAIN in case no signal is available.

If the size of the buffer passed to read(2) is lower than sizeof(struct
signalfd_siginfo), -EINVAL is returned.  A read from the signalfd can also
return -ERESTARTSYS in case a signal hits the process.  The format of the
struct signalfd_siginfo is, and the valid fields depends of the (->code &
__SI_MASK) value, in the same way a struct siginfo would:

struct signalfd_siginfo {
	__u32 signo;	/* si_signo */
	__s32 err;	/* si_errno */
	__s32 code;	/* si_code */
	__u32 pid;	/* si_pid */
	__u32 uid;	/* si_uid */
	__s32 fd;	/* si_fd */
	__u32 tid;	/* si_fd */
	__u32 band;	/* si_band */
	__u32 overrun;	/* si_overrun */
	__u32 trapno;	/* si_trapno */
	__s32 status;	/* si_status */
	__s32 svint;	/* si_int */
	__u64 svptr;	/* si_ptr */
	__u64 utime;	/* si_utime */
	__u64 stime;	/* si_stime */
	__u64 addr;	/* si_addr */
};

[akpm@linux-foundation.org: fix signalfd_copyinfo() on i386]
Signed-off-by: NDavide Libenzi <davidel@xmailserver.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      fba2afaa
    • E
      getrusage(): fill ru_inblock and ru_oublock fields if possible · 6eaeeaba
      由 Eric Dumazet 提交于 
      If CONFIG_TASK_IO_ACCOUNTING is defined, we update io accounting counters for
each task.

This patch permits reporting of values using the well known getrusage()
syscall, filling ru_inblock and ru_oublock instead of null values.

As TASK_IO_ACCOUNTING currently counts bytes counts, we approximate blocks
count doing : nr_blocks = nr_bytes / 512

Example of use :
----------------------
After patch is applied, /usr/bin/time command can now give a good
approximation of IO that the process had to do.

$ /usr/bin/time grep tototo /usr/include/*
Command exited with non-zero status 1
0.00user 0.02system 0:02.11elapsed 1%CPU (0avgtext+0avgdata 0maxresident)k
24288inputs+0outputs (0major+259minor)pagefaults 0swaps

$ /usr/bin/time dd if=/dev/zero of=/tmp/testfile count=1000
1000+0 enregistrements lus
1000+0 enregistrements écrits
512000 octets (512 kB) copiés, 0,00326601 seconde, 157 MB/s
0.00user 0.00system 0:00.00elapsed 80%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+3000outputs (0major+299minor)pagefaults 0swaps
Signed-off-by: NEric Dumazet <dada1@cosmosbay.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      6eaeeaba
    • N
      When stacked block devices are in-use (e.g. md or dm), the recursive calls · d89d8796
      由 Neil Brown 提交于 
      to generic_make_request can use up a lot of space, and we would rather they
didn't.

As generic_make_request is a void function, and as it is generally not
expected that it will have any effect immediately, it is safe to delay any
call to generic_make_request until there is sufficient stack space
available.

As ->bi_next is reserved for the driver to use, it can have no valid value
when generic_make_request is called, and as __make_request implicitly
assumes it will be NULL (ELEVATOR_BACK_MERGE fork of switch) we can be
certain that all callers set it to NULL.  We can therefore safely use
bi_next to link pending requests together, providing we clear it before
making the real call.

So, we choose to allow each thread to only be active in one
generic_make_request at a time.  If a subsequent (recursive) call is made,
the bio is linked into a per-thread list, and is handled when the active
call completes.

As the list of pending bios is per-thread, there are no locking issues to
worry about.

I say above that it is "safe to delay any call...".  There are, however,
some behaviours of a make_request_fn which would make it unsafe.  These
include any behaviour that assumes anything will have changed after a
recursive call to generic_make_request.

These could include:
 - waiting for that call to finish and call it's bi_end_io function.
   md use to sometimes do this (marking the superblock dirty before
   completing a write) but doesn't any more
 - inspecting the bio for fields that generic_make_request might
   change, such as bi_sector or bi_bdev.  It is hard to see a good
   reason for this, and I don't think anyone actually does it.
 - inspecing the queue to see if, e.g. it is 'full' yet.  Again, I
   think this is very unlikely to be useful, or to be done.
Signed-off-by: NNeil Brown <neilb@suse.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: <dm-devel@redhat.com>

Alasdair G Kergon <agk@redhat.com> said:

 I can see nothing wrong with this in principle.

 For device-mapper at the moment though it's essential that, while the bio
 mappings may now get delayed, they still get processed in exactly
 the same order as they were passed to generic_make_request().

 My main concern is whether the timing changes implicit in this patch
 will make the rare data-corrupting races in the existing snapshot code
 more likely. (I'm working on a fix for these races, but the unfinished
 patch is already several hundred lines long.)

 It would be helpful if some people on this mailing list would test
 this patch in various scenarios and report back.
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>
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