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  1. 16 4月, 2018 1 次提交
  3. 19 3月, 2018 1 次提交
    • M
      buffer.c: call thaw_super during emergency thaw · 08fdc8a0
      由 Mateusz Guzik 提交于 
      There are 2 distinct freezing mechanisms - one operates on block
devices and another one directly on super blocks. Both end up with the
same result, but thaw of only one of these does not thaw the other.

In particular fsfreeze --freeze uses the ioctl variant going to the
super block. Since prior to this patch emergency thaw was not doing
a relevant thaw, filesystems frozen with this method remained
unaffected.

The patch is a hack which adds blind unfreezing.

In order to keep the super block write-locked the whole time the code
is shuffled around and the newly introduced __iterate_supers is
employed.
Signed-off-by: NMateusz Guzik <mguzik@redhat.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      08fdc8a0
  5. 26 12月, 2017 1 次提交
    • N
      VFS: don't keep disconnected dentries on d_anon · f1ee6162
      由 NeilBrown 提交于 
      The original purpose of the per-superblock d_anon list was to
keep disconnected dentries in the cache between consecutive
requests to the NFS server.  Dentries can be disconnected if
a client holds a file open and repeatedly performs IO on it,
and if the server drops the dentry, whether due to memory
pressure, server restart, or "echo 3 > /proc/sys/vm/drop_caches".

This purpose was thwarted by commit 75a6f82a ("freeing unlinked
file indefinitely delayed") which caused disconnected dentries
to be freed as soon as their refcount reached zero.

This means that, when a dentry being used by nfsd gets disconnected, a
new one needs to be allocated for every request (unless requests
overlap).  As the dentry has no name, no parent, and no children,
there is little of value to cache.  As small memory allocations are
typically fast (from per-cpu free lists) this likely has little cost.

This means that the original purpose of s_anon is no longer relevant:
there is no longer any need to keep disconnected dentries on a list so
they appear to be hashed.

However, s_anon now has a new use.  When you mount an NFS filesystem,
the dentry stored in s_root is just a placebo.  The "real" root dentry
is allocated using d_obtain_root() and so it kept on the s_anon list.
I don't know the reason for this, but suspect it related to NFSv4
where a mount of "server:/some/path" require NFS to look up the root
filehandle on the server, then walk down "/some" and "/path" to get
the filehandle to mount.

Whatever the reason, NFS depends on the s_anon list and on
shrink_dcache_for_umount() pruning all dentries on this list.  So we
cannot simply remove s_anon.

We could just leave the code unchanged, but apart from that being
potentially confusing, the (unfair) bit-spin-lock which protects
s_anon can become a bottle neck when lots of disconnected dentries are
being created.

So this patch renames s_anon to s_roots, and stops storing
disconnected dentries on the list.  Only dentries obtained with
d_obtain_root() are now stored on this list.  There are many fewer of
these (only NFS and NILFS2 use the call, and only during filesystem
mount) so contention on the bit-lock will not be a problem.

Possibly an alternate solution should be found for NFS and NILFS2, but
that would require understanding their needs first.
Signed-off-by: NNeilBrown <neilb@suse.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
      f1ee6162
  7. 19 12月, 2017 1 次提交
  9. 05 12月, 2017 1 次提交
  11. 02 11月, 2017 1 次提交
    • G
      License cleanup: add SPDX GPL-2.0 license identifier to files with no license · b2441318
      由 Greg Kroah-Hartman 提交于 
      Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.

By default all files without license information are under the default
license of the kernel, which is GPL version 2.

Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier.  The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.

This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.

How this work was done:

Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
 - file had no licensing information it it.
 - file was a */uapi/* one with no licensing information in it,
 - file was a */uapi/* one with existing licensing information,

Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.

The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne.  Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.

The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed.  Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.

Criteria used to select files for SPDX license identifier tagging was:
 - Files considered eligible had to be source code files.
 - Make and config files were included as candidates if they contained >5
   lines of source
 - File already had some variant of a license header in it (even if <5
   lines).

All documentation files were explicitly excluded.

The following heuristics were used to determine which SPDX license
identifiers to apply.

 - when both scanners couldn't find any license traces, file was
   considered to have no license information in it, and the top level
   COPYING file license applied.

   For non */uapi/* files that summary was:

   SPDX license identifier                            # files
   ---------------------------------------------------|-------
   GPL-2.0                                              11139

   and resulted in the first patch in this series.

   If that file was a */uapi/* path one, it was "GPL-2.0 WITH
   Linux-syscall-note" otherwise it was "GPL-2.0".  Results of that was:

   SPDX license identifier                            # files
   ---------------------------------------------------|-------
   GPL-2.0 WITH Linux-syscall-note                        930

   and resulted in the second patch in this series.

 - if a file had some form of licensing information in it, and was one
   of the */uapi/* ones, it was denoted with the Linux-syscall-note if
   any GPL family license was found in the file or had no licensing in
   it (per prior point).  Results summary:

   SPDX license identifier                            # files
   ---------------------------------------------------|------
   GPL-2.0 WITH Linux-syscall-note                       270
   GPL-2.0+ WITH Linux-syscall-note                      169
   ((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause)    21
   ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause)    17
   LGPL-2.1+ WITH Linux-syscall-note                      15
   GPL-1.0+ WITH Linux-syscall-note                       14
   ((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause)    5
   LGPL-2.0+ WITH Linux-syscall-note                       4
   LGPL-2.1 WITH Linux-syscall-note                        3
   ((GPL-2.0 WITH Linux-syscall-note) OR MIT)              3
   ((GPL-2.0 WITH Linux-syscall-note) AND MIT)             1

   and that resulted in the third patch in this series.

 - when the two scanners agreed on the detected license(s), that became
   the concluded license(s).

 - when there was disagreement between the two scanners (one detected a
   license but the other didn't, or they both detected different
   licenses) a manual inspection of the file occurred.

 - In most cases a manual inspection of the information in the file
   resulted in a clear resolution of the license that should apply (and
   which scanner probably needed to revisit its heuristics).

 - When it was not immediately clear, the license identifier was
   confirmed with lawyers working with the Linux Foundation.

 - If there was any question as to the appropriate license identifier,
   the file was flagged for further research and to be revisited later
   in time.

In total, over 70 hours of logged manual review was done on the
spreadsheet to determine the SPDX license identifiers to apply to the
source files by Kate, Philippe, Thomas and, in some cases, confirmation
by lawyers working with the Linux Foundation.

Kate also obtained a third independent scan of the 4.13 code base from
FOSSology, and compared selected files where the other two scanners
disagreed against that SPDX file, to see if there was new insights.  The
Windriver scanner is based on an older version of FOSSology in part, so
they are related.

Thomas did random spot checks in about 500 files from the spreadsheets
for the uapi headers and agreed with SPDX license identifier in the
files he inspected. For the non-uapi files Thomas did random spot checks
in about 15000 files.

In initial set of patches against 4.14-rc6, 3 files were found to have
copy/paste license identifier errors, and have been fixed to reflect the
correct identifier.

Additionally Philippe spent 10 hours this week doing a detailed manual
inspection and review of the 12,461 patched files from the initial patch
version early this week with:
 - a full scancode scan run, collecting the matched texts, detected
   license ids and scores
 - reviewing anything where there was a license detected (about 500+
   files) to ensure that the applied SPDX license was correct
 - reviewing anything where there was no detection but the patch license
   was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
   SPDX license was correct

This produced a worksheet with 20 files needing minor correction.  This
worksheet was then exported into 3 different .csv files for the
different types of files to be modified.

These .csv files were then reviewed by Greg.  Thomas wrote a script to
parse the csv files and add the proper SPDX tag to the file, in the
format that the file expected.  This script was further refined by Greg
based on the output to detect more types of files automatically and to
distinguish between header and source .c files (which need different
comment types.)  Finally Greg ran the script using the .csv files to
generate the patches.
Reviewed-by: NKate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: NPhilippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      b2441318
  13. 12 10月, 2017 2 次提交
  15. 05 10月, 2017 1 次提交
  17. 18 8月, 2017 1 次提交
  19. 17 7月, 2017 2 次提交
    • D
      VFS: Differentiate mount flags (MS_*) from internal superblock flags · e462ec50
      由 David Howells 提交于 
      Differentiate the MS_* flags passed to mount(2) from the internal flags set
in the super_block's s_flags.  s_flags are now called SB_*, with the names
and the values for the moment mirroring the MS_* flags that they're
equivalent to.

In this patch, just the headers are altered and some kernel code where
blind automated conversion isn't necessarily correct.

Note that this shows up some interesting issues:

 (1) Some MS_* flags get translated to MNT_* flags (such as MS_NODEV ->
     MNT_NODEV) without passing this on to the filesystem, but some
     filesystems set such flags anyway.

 (2) The ->remount_fs() methods of some filesystems adjust the *flags
     argument by setting MS_* flags in it, such as MS_NOATIME - but these
     flags are then scrubbed by do_remount_sb() (only the occupants of
     MS_RMT_MASK are permitted: MS_RDONLY, MS_SYNCHRONOUS, MS_MANDLOCK,
     MS_I_VERSION and MS_LAZYTIME)

I'm not sure what's the best way to solve all these cases.
Suggested-by: NAl Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: NDavid Howells <dhowells@redhat.com>
      e462ec50
    • D
      VFS: Convert sb->s_flags & MS_RDONLY to sb_rdonly(sb) · bc98a42c
      由 David Howells 提交于 
      Firstly by applying the following with coccinelle's spatch:

	@@ expression SB; @@
	-SB->s_flags & MS_RDONLY
	+sb_rdonly(SB)

to effect the conversion to sb_rdonly(sb), then by applying:

	@@ expression A, SB; @@
	(
	-(!sb_rdonly(SB)) && A
	+!sb_rdonly(SB) && A
	|
	-A != (sb_rdonly(SB))
	+A != sb_rdonly(SB)
	|
	-A == (sb_rdonly(SB))
	+A == sb_rdonly(SB)
	|
	-!(sb_rdonly(SB))
	+!sb_rdonly(SB)
	|
	-A && (sb_rdonly(SB))
	+A && sb_rdonly(SB)
	|
	-A || (sb_rdonly(SB))
	+A || sb_rdonly(SB)
	|
	-(sb_rdonly(SB)) != A
	+sb_rdonly(SB) != A
	|
	-(sb_rdonly(SB)) == A
	+sb_rdonly(SB) == A
	|
	-(sb_rdonly(SB)) && A
	+sb_rdonly(SB) && A
	|
	-(sb_rdonly(SB)) || A
	+sb_rdonly(SB) || A
	)

	@@ expression A, B, SB; @@
	(
	-(sb_rdonly(SB)) ? 1 : 0
	+sb_rdonly(SB)
	|
	-(sb_rdonly(SB)) ? A : B
	+sb_rdonly(SB) ? A : B
	)

to remove left over excess bracketage and finally by applying:

	@@ expression A, SB; @@
	(
	-(A & MS_RDONLY) != sb_rdonly(SB)
	+(bool)(A & MS_RDONLY) != sb_rdonly(SB)
	|
	-(A & MS_RDONLY) == sb_rdonly(SB)
	+(bool)(A & MS_RDONLY) == sb_rdonly(SB)
	)

to make comparisons against the result of sb_rdonly() (which is a bool)
work correctly.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
      bc98a42c
  21. 11 7月, 2017 1 次提交
  23. 06 7月, 2017 1 次提交
  25. 21 4月, 2017 4 次提交
  27. 02 2月, 2017 1 次提交
  29. 01 2月, 2017 1 次提交
    • E
      fs: Better permission checking for submounts · 93faccbb
      由 Eric W. Biederman 提交于 
      To support unprivileged users mounting filesystems two permission
checks have to be performed: a test to see if the user allowed to
create a mount in the mount namespace, and a test to see if
the user is allowed to access the specified filesystem.

The automount case is special in that mounting the original filesystem
grants permission to mount the sub-filesystems, to any user who
happens to stumble across the their mountpoint and satisfies the
ordinary filesystem permission checks.

Attempting to handle the automount case by using override_creds
almost works.  It preserves the idea that permission to mount
the original filesystem is permission to mount the sub-filesystem.
Unfortunately using override_creds messes up the filesystems
ordinary permission checks.

Solve this by being explicit that a mount is a submount by introducing
vfs_submount, and using it where appropriate.

vfs_submount uses a new mount internal mount flags MS_SUBMOUNT, to let
sget and friends know that a mount is a submount so they can take appropriate
action.

sget and sget_userns are modified to not perform any permission checks
on submounts.

follow_automount is modified to stop using override_creds as that
has proven problemantic.

do_mount is modified to always remove the new MS_SUBMOUNT flag so
that we know userspace will never by able to specify it.

autofs4 is modified to stop using current_real_cred that was put in
there to handle the previous version of submount permission checking.

cifs is modified to pass the mountpoint all of the way down to vfs_submount.

debugfs is modified to pass the mountpoint all of the way down to
trace_automount by adding a new parameter.  To make this change easier
a new typedef debugfs_automount_t is introduced to capture the type of
the debugfs automount function.

Cc: stable@vger.kernel.org
Fixes: 069d5ac9 ("autofs:  Fix automounts by using current_real_cred()->uid")
Fixes: aeaa4a79 ("fs: Call d_automount with the filesystems creds")
Reviewed-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Reviewed-by: NSeth Forshee <seth.forshee@canonical.com>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
      93faccbb
  31. 30 11月, 2016 1 次提交
    • J
      quota: Remove dqonoff_mutex · c3b00446
      由 Jan Kara 提交于 
      The only places that were grabbing dqonoff_mutex are functions turning
quotas on and off and these are properly serialized using s_umount
semaphore. Remove dqonoff_mutex.
Signed-off-by: NJan Kara <jack@suse.cz>
      c3b00446
  33. 23 11月, 2016 1 次提交
  35. 15 10月, 2016 2 次提交
  37. 27 7月, 2016 1 次提交
  39. 24 6月, 2016 5 次提交
    • E
      userns: Remove the now unnecessary FS_USERNS_DEV_MOUNT flag · cc50a07a
      由 Eric W. Biederman 提交于 
      Now that SB_I_NODEV controls the nodev behavior devpts can just clear
this flag during mount.  Simplifying the code and making it easier
to audit how the code works.  While still preserving the invariant
that s_iflags is only modified during mount.
Acked-by: NSeth Forshee <seth.forshee@canonical.com>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
      cc50a07a
    • E
      userns: Remove implicit MNT_NODEV fragility. · 67690f93
      由 Eric W. Biederman 提交于 
      Replace the implict setting of MNT_NODEV on mounts that happen with
just user namespace permissions with an implicit setting of SB_I_NODEV
in s_iflags.  The visibility of the implicit MNT_NODEV has caused
problems in the past.

With this change the fragile case where an implicit MNT_NODEV needs to
be preserved in do_remount is removed.  Using SB_I_NODEV is much less
fragile as s_iflags are set during the original mount and never
changed.

In do_new_mount with the implicit setting of MNT_NODEV gone, the only
code that can affect mnt_flags is fs_fully_visible so simplify the if
statement and reduce the indentation of the code to make that clear.
Acked-by: NSeth Forshee <seth.forshee@canonical.com>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
      67690f93
    • E
      mnt: Move the FS_USERNS_MOUNT check into sget_userns · a001e74c
      由 Eric W. Biederman 提交于 
      Allowing a filesystem to be mounted by other than root in the initial
user namespace is a filesystem property not a mount namespace property
and as such should be checked in filesystem specific code.  Move the
FS_USERNS_MOUNT test into super.c:sget_userns().
Acked-by: NSeth Forshee <seth.forshee@canonical.com>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
      a001e74c
    • E
      fs: Add user namespace member to struct super_block · 6e4eab57
      由 Eric W. Biederman 提交于 
      Start marking filesystems with a user namespace owner, s_user_ns.  In
this change this is only used for permission checks of who may mount a
filesystem.  Ultimately s_user_ns will be used for translating ids and
checking capabilities for filesystems mounted from user namespaces.

The default policy for setting s_user_ns is implemented in sget(),
which arranges for s_user_ns to be set to current_user_ns() and to
ensure that the mounter of the filesystem has CAP_SYS_ADMIN in that
user_ns.

The guts of sget are split out into another function sget_userns().
The function sget_userns calls alloc_super with the specified user
namespace or it verifies the existing superblock that was found
has the expected user namespace, and fails with EBUSY when it is not.
This failing prevents users with the wrong privileges mounting a
filesystem.

The reason for the split of sget_userns from sget is that in some
cases such as mount_ns and kernfs_mount_ns a different policy for
permission checking of mounts and setting s_user_ns is necessary, and
the existence of sget_userns() allows those policies to be
implemented.

The helper mount_ns is expected to be used for filesystems such as
proc and mqueuefs which present per namespace information.  The
function mount_ns is modified to call sget_userns instead of sget to
ensure the user namespace owner of the namespace whose information is
presented by the filesystem is used on the superblock.

For sysfs and cgroup the appropriate permission checks are already in
place, and kernfs_mount_ns is modified to call sget_userns so that
the init_user_ns is the only user namespace used.

For the cgroup filesystem cgroup namespace mounts are bind mounts of a
subset of the full cgroup filesystem and as such s_user_ns must be the
same for all of them as there is only a single superblock.

Mounts of sysfs that vary based on the network namespace could in principle
change s_user_ns but it keeps the analysis and implementation of kernfs
simpler if that is not supported, and at present there appear to be no
benefits from supporting a different s_user_ns on any sysfs mount.

Getting the details of setting s_user_ns correct has been
a long process.  Thanks to Pavel Tikhorirorv who spotted a leak
in sget_userns.  Thanks to Seth Forshee who has kept the work alive.

Thanks-to: Seth Forshee <seth.forshee@canonical.com>
Thanks-to: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Acked-by: NSeth Forshee <seth.forshee@canonical.com>
Signed-off-by: NEric W. Biederman <ebiederm@xmission.com>
      6e4eab57
    • E
      vfs: Pass data, ns, and ns->userns to mount_ns · d91ee87d
      由 Eric W. Biederman 提交于 
      Today what is normally called data (the mount options) is not passed
to fill_super through mount_ns.

Pass the mount options and the namespace separately to mount_ns so
that filesystems such as proc that have mount options, can use
mount_ns.

Pass the user namespace to mount_ns so that the standard permission
check that verifies the mounter has permissions over the namespace can
be performed in mount_ns instead of in each filesystems .mount method.
Thus removing the duplication between mqueuefs and proc in terms of
permission checks.  The extra permission check does not currently
affect the rpc_pipefs filesystem and the nfsd filesystem as those
filesystems do not currently allow unprivileged mounts.  Without
unpvileged mounts it is guaranteed that the caller has already passed
capable(CAP_SYS_ADMIN) which guarantees extra permission check will
pass.

Update rpc_pipefs and the nfsd filesystem to ensure that the network
namespace reference is always taken in fill_super and always put in kill_sb
so that the logic is simpler and so that errors originating inside of
fill_super do not cause a network namespace leak.
Acked-by: NSeth Forshee <seth.forshee@canonical.com>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>
      d91ee87d
  41. 18 4月, 2016 1 次提交
  43. 04 3月, 2016 1 次提交
    • T
      writeback: flush inode cgroup wb switches instead of pinning super_block · a1a0e23e
      由 Tejun Heo 提交于 
      If cgroup writeback is in use, inodes can be scheduled for
asynchronous wb switching.  Before 5ff8eaac ("writeback: keep
superblock pinned during cgroup writeback association switches"), this
could race with umount leading to super_block being destroyed while
inodes are pinned for wb switching.  5ff8eaac fixed it by bumping
s_active while wb switches are in flight; however, this allowed
in-flight wb switches to make umounts asynchronous when the userland
expected synchronosity - e.g. fsck immediately following umount may
fail because the device is still busy.

This patch removes the problematic super_block pinning and instead
makes generic_shutdown_super() flush in-flight wb switches.  wb
switches are now executed on a dedicated isw_wq so that they can be
flushed and isw_nr_in_flight keeps track of the number of in-flight wb
switches so that flushing can be avoided in most cases.

v2: Move cgroup_writeback_umount() further below and add MS_ACTIVE
    check in inode_switch_wbs() as Jan an Al suggested.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-by: NTahsin Erdogan <tahsin@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Link: http://lkml.kernel.org/g/CAAeU0aNCq7LGODvVGRU-oU_o-6enii5ey0p1c26D1ZzYwkDc5A@mail.gmail.com
Fixes: 5ff8eaac ("writeback: keep superblock pinned during cgroup writeback association switches")
Cc: stable@vger.kernel.org #v4.5
Reviewed-by: NJan Kara <jack@suse.cz>
Tested-by: NTahsin Erdogan <tahsin@google.com>
Signed-off-by: NJens Axboe <axboe@fb.com>
      a1a0e23e
  45. 07 1月, 2016 1 次提交
  47. 08 12月, 2015 1 次提交
  49. 18 8月, 2015 2 次提交
  51. 15 8月, 2015 4 次提交
    • O
      change sb_writers to use percpu_rw_semaphore · 8129ed29
      由 Oleg Nesterov 提交于 
      We can remove everything from struct sb_writers except frozen
and add the array of percpu_rw_semaphore's instead.

This patch doesn't remove sb_writers->wait_unfrozen yet, we keep
it for get_super_thawed(). We will probably remove it later.

This change tries to address the following problems:

	- Firstly, __sb_start_write() looks simply buggy. It does
	  __sb_end_write() if it sees ->frozen, but if it migrates
	  to another CPU before percpu_counter_dec(), sb_wait_write()
	  can wrongly succeed if there is another task which holds
	  the same "semaphore": sb_wait_write() can miss the result
	  of the previous percpu_counter_inc() but see the result
	  of this percpu_counter_dec().

	- As Dave Hansen reports, it is suboptimal. The trivial
	  microbenchmark that writes to a tmpfs file in a loop runs
	  12% faster if we change this code to rely on RCU and kill
	  the memory barriers.

	- This code doesn't look simple. It would be better to rely
	  on the generic locking code.

	  According to Dave, this change adds the same performance
	  improvement.

Note: with this change both freeze_super() and thaw_super() will do
synchronize_sched_expedited() 3 times. This is just ugly. But:

	- This will be "fixed" by the rcu_sync changes we are going
	  to merge. After that freeze_super()->percpu_down_write()
	  will use synchronize_sched(), and thaw_super() won't use
	  synchronize() at all.

	  This doesn't need any changes in fs/super.c.

	- Once we merge rcu_sync changes, we can also change super.c
	  so that all wb_write->rw_sem's will share the single ->rss
	  in struct sb_writes, then freeze_super() will need only one
	  synchronize_sched().
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Reviewed-by: NJan Kara <jack@suse.com>
      8129ed29
    • O
      shift percpu_counter_destroy() into destroy_super_work() · 853b39a7
      由 Oleg Nesterov 提交于 
      Of course, this patch is ugly as hell. It will be (partially)
reverted later. We add it to ensure that other WIP changes in
percpu_rw_semaphore won't break fs/super.c.

We do not even need this change right now, percpu_free_rwsem()
is fine in atomic context. But we are going to change this, it
will be might_sleep() after we merge the rcu_sync() patches.

And even after that we do not really need destroy_super_work(),
we will kill it in any case. Instead, destroy_super_rcu() should
just check that rss->cb_state == CB_IDLE and do call_rcu() again
in the (very unlikely) case this is not true.

So this is just the temporary kludge which helps us to avoid the
conflicts with the changes which will be (hopefully) routed via
rcu tree.
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Reviewed-by: NJan Kara <jack@suse.com>
      853b39a7
    • O
      document rwsem_release() in sb_wait_write() · 0e28e01f
      由 Oleg Nesterov 提交于 
      Not only we need to avoid the warning from lockdep_sys_exit(), the
caller of freeze_super() can never release this lock. Another thread
can do this, so there is another reason for rwsem_release().

Plus the comment should explain why we have to fool lockdep.
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Reviewed-by: NJan Kara <jack@suse.com>
      0e28e01f
    • O
      fix the broken lockdep logic in __sb_start_write() · f4b554af
      由 Oleg Nesterov 提交于 
      1. wait_event(frozen < level) without rwsem_acquire_read() is just
   wrong from lockdep perspective. If we are going to deadlock
   because the caller is buggy, lockdep can't detect this problem.

2. __sb_start_write() can race with thaw_super() + freeze_super(),
   and after "goto retry" the 2nd  acquire_freeze_lock() is wrong.

3. The "tell lockdep we are doing trylock" hack doesn't look nice.

   I think this is correct, but this logic should be more explicit.
   Yes, the recursive read_lock() is fine if we hold the lock on a
   higher level. But we do not need to fool lockdep. If we can not
   deadlock in this case then try-lock must not fail and we can use
   use wait == F throughout this code.

Note: as Dave Chinner explains, the "trylock" hack and the fat comment
can be probably removed. But this needs a separate change and it will
be trivial: just kill __sb_start_write() and rename do_sb_start_write()
back to __sb_start_write().
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Reviewed-by: NJan Kara <jack@suse.com>
      f4b554af