linux.git/fs/fscache/cache.c, branch v5.8

docs: filesystems: caching/backend-api.txt: convert it to ReST

2020-05-05T15:22:21+00:00

- Add a SPDX header;
- Adjust document and section titles;
- Some whitespace fixes and new line breaks;
- Mark literal blocks as such;
- Add table markups;
- Add it to filesystems/caching/index.rst.

Signed-off-by: Mauro Carvalho Chehab 
Link: https://lore.kernel.org/r/5d0a61abaa87bfe913b9e2f321e74ef7af0f3dfc.1588021877.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152

2019-05-30T18:26:32+00:00

Based on 1 normalized pattern(s):

  this program is free software you can redistribute it and or modify
  it under the terms of the gnu general public license as published by
  the free software foundation either version 2 of the license or at
  your option any later version

extracted by the scancode license scanner the SPDX license identifier

  GPL-2.0-or-later

has been chosen to replace the boilerplate/reference in 3029 file(s).

Signed-off-by: Thomas Gleixner 
Reviewed-by: Allison Randal 
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190527070032.746973796@linutronix.de
Signed-off-by: Greg Kroah-Hartman

fscache: Fix reference overput in fscache_attach_object() error handling

2018-07-25T13:49:00+00:00

When a cookie is allocated that causes fscache_object structs to be
allocated, those objects are initialised with the cookie pointer, but
aren't blessed with a ref on that cookie unless the attachment is
successfully completed in fscache_attach_object().

If attachment fails because the parent object was dying or there was a
collision, fscache_attach_object() returns without incrementing the cookie
counter - but upon failure of this function, the object is released which
then puts the cookie, whether or not a ref was taken on the cookie.

Fix this by taking a ref on the cookie when it is assigned in
fscache_object_init(), even when we're creating a root object.


Analysis from Kiran Kumar:

This bug has been seen in 4.4.0-124-generic #148-Ubuntu kernel

BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1776277

fscache cookie ref count updated incorrectly during fscache object
allocation resulting in following Oops.

kernel BUG at /build/linux-Y09MKI/linux-4.4.0/fs/fscache/internal.h:321!
kernel BUG at /build/linux-Y09MKI/linux-4.4.0/fs/fscache/cookie.c:639!

[Cause]
Two threads are trying to do operate on a cookie and two objects.

(1) One thread tries to unmount the filesystem and in process goes over a
    huge list of objects marking them dead and deleting the objects.
    cookie->usage is also decremented in following path:

      nfs_fscache_release_super_cookie
       -> __fscache_relinquish_cookie
        ->__fscache_cookie_put
        ->BUG_ON(atomic_read(&cookie->usage) <= 0);

(2) A second thread tries to lookup an object for reading data in following
    path:

    fscache_alloc_object
    1) cachefiles_alloc_object
        -> fscache_object_init
           -> assign cookie, but usage not bumped.
    2) fscache_attach_object -> fails in cant_attach_object because the
         cookie's backing object or cookie's->parent object are going away
    3) fscache_put_object
        -> cachefiles_put_object
          ->fscache_object_destroy
            ->fscache_cookie_put
               ->BUG_ON(atomic_read(&cookie->usage) <= 0);

[NOTE from dhowells] It's unclear as to the circumstances in which (2) can
take place, given that thread (1) is in nfs_kill_super(), however a
conflicting NFS mount with slightly different parameters that creates a
different superblock would do it.  A backtrace from Kiran seems to show
that this is a possibility:

    kernel BUG at/build/linux-Y09MKI/linux-4.4.0/fs/fscache/cookie.c:639!
    ...
    RIP: __fscache_cookie_put+0x3a/0x40 [fscache]
    Call Trace:
     __fscache_relinquish_cookie+0x87/0x120 [fscache]
     nfs_fscache_release_super_cookie+0x2d/0xb0 [nfs]
     nfs_kill_super+0x29/0x40 [nfs]
     deactivate_locked_super+0x48/0x80
     deactivate_super+0x5c/0x60
     cleanup_mnt+0x3f/0x90
     __cleanup_mnt+0x12/0x20
     task_work_run+0x86/0xb0
     exit_to_usermode_loop+0xc2/0xd0
     syscall_return_slowpath+0x4e/0x60
     int_ret_from_sys_call+0x25/0x9f

[Fix] Bump up the cookie usage in fscache_object_init, when it is first
being assigned a cookie atomically such that the cookie is added and bumped
up if its refcount is not zero.  Remove the assignment in
fscache_attach_object().

[Testcase]
I have run ~100 hours of NFS stress tests and not seen this bug recur.

[Regression Potential]
 - Limited to fscache/cachefiles.

Fixes: ccc4fc3d11e9 ("FS-Cache: Implement the cookie management part of the netfs API")
Signed-off-by: Kiran Kumar Modukuri 
Signed-off-by: David Howells

fscache: Attach the index key and aux data to the cookie

2018-04-04T12:41:28+00:00

Attach copies of the index key and auxiliary data to the fscache cookie so
that:

 (1) The callbacks to the netfs for this stuff can be eliminated.  This
     can simplify things in the cache as the information is still
     available, even after the cache has relinquished the cookie.

 (2) Simplifies the locking requirements of accessing the information as we
     don't have to worry about the netfs object going away on us.

 (3) The cache can do lazy updating of the coherency information on disk.
     As long as the cache is flushed before reboot/poweroff, there's no
     need to update the coherency info on disk every time it changes.

 (4) Cookies can be hashed or put in a tree as the index key is easily
     available.  This allows:

     (a) Checks for duplicate cookies can be made at the top fscache layer
     	 rather than down in the bowels of the cache backend.

     (b) Caching can be added to a netfs object that has a cookie if the
     	 cache is brought online after the netfs object is allocated.

A certain amount of space is made in the cookie for inline copies of the
data, but if it won't fit there, extra memory will be allocated for it.

The downside of this is that live cache operation requires more memory.

Signed-off-by: David Howells 
Acked-by: Anna Schumaker 
Tested-by: Steve Dickson

fs/fscache: convert printk to pr_foo()

2014-06-04T23:53:51+00:00

All printk converted to pr_foo() except internal.h: printk(KERN_DEBUG

Coalesce formats.

Add pr_fmt

Signed-off-by: Fabian Frederick 
Cc: David Howells 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

FS-Cache: Fix object state machine to have separate work and wait states

2013-06-19T13:16:47+00:00

Fix object state machine to have separate work and wait states as that makes
it easier to envision.

There are now three kinds of state:

 (1) Work state.  This is an execution state.  No event processing is performed
     by a work state.  The function attached to a work state returns a pointer
     indicating the next state to which the OSM should transition.  Returning
     NO_TRANSIT repeats the current state, but goes back to the scheduler
     first.

 (2) Wait state.  This is an event processing state.  No execution is
     performed by a wait state.  Wait states are just tables of "if event X
     occurs, clear it and transition to state Y".  The dispatcher returns to
     the scheduler if none of the events in which the wait state has an
     interest are currently pending.

 (3) Out-of-band state.  This is a special work state.  Transitions to normal
     states can be overridden when an unexpected event occurs (eg. I/O error).
     Instead the dispatcher disables and clears the OOB event and transits to
     the specified work state.  This then acts as an ordinary work state,
     though object->state points to the overridden destination.  Returning
     NO_TRANSIT resumes the overridden transition.

In addition, the states have names in their definitions, so there's no need for
tables of state names.  Further, the EV_REQUEUE event is no longer necessary as
that is automatic for work states.

Since the states are now separate structs rather than values in an enum, it's
not possible to use comparisons other than (non-)equality between them, so use
some object->flags to indicate what phase an object is in.

The EV_RELEASE, EV_RETIRE and EV_WITHDRAW events have been squished into one
(EV_KILL).  An object flag now carries the information about retirement.

Similarly, the RELEASING, RECYCLING and WITHDRAWING states have been merged
into an KILL_OBJECT state and additional states have been added for handling
waiting dependent objects (JUMPSTART_DEPS and KILL_DEPENDENTS).

A state has also been added for synchronising with parent object initialisation
(WAIT_FOR_PARENT) and another for initiating look up (PARENT_READY).

Signed-off-by: David Howells 
Tested-By: Milosz Tanski 
Acked-by: Jeff Layton

FS-Cache: Wrap checks on object state

2013-06-19T13:16:47+00:00

Wrap checks on object state (mostly outside of fs/fscache/object.c) with
inline functions so that the mechanism can be replaced.

Some of the state checks within object.c are left as-is as they will be
replaced.

Signed-off-by: David Howells 
Tested-By: Milosz Tanski 
Acked-by: Jeff Layton

FS-Cache: Limit the number of I/O error reports for a cache

2012-12-20T22:10:44+00:00

Limit the number of I/O error reports for a cache to 1 to prevent massive
amounts of noise.  After the first I/O error the cache is taken off line
automatically, so must be restarted to resume caching.

Signed-off-by: David Howells

FS-Cache: Add counters for entry/exit to/from cache operation functions

2009-11-19T18:11:08+00:00

Count entries to and exits from cache operation table functions.  Maintain
these as a single counter that's added to or removed from as appropriate.

Signed-off-by: David Howells

FS-Cache: Allow the current state of all objects to be dumped

2009-11-19T18:11:04+00:00

Allow the current state of all fscache objects to be dumped by doing:

	cat /proc/fs/fscache/objects

By default, all objects and all fields will be shown.  This can be restricted
by adding a suitable key to one of the caller's keyrings (such as the session
keyring):

	keyctl add user fscache:objlist "" @s

The  are:

	K	Show hexdump of object key (don't show if not given)
	A	Show hexdump of object aux data (don't show if not given)

And paired restrictions:

	C	Show objects that have a cookie
	c	Show objects that don't have a cookie
	B	Show objects that are busy
	b	Show objects that aren't busy
	W	Show objects that have pending writes
	w	Show objects that don't have pending writes
	R	Show objects that have outstanding reads
	r	Show objects that don't have outstanding reads
	S	Show objects that have slow work queued
	s	Show objects that don't have slow work queued

If neither side of a restriction pair is given, then both are implied.  For
example:

	keyctl add user fscache:objlist KB @s

shows objects that are busy, and lists their object keys, but does not dump
their auxiliary data.  It also implies "CcWwRrSs", but as 'B' is given, 'b' is
not implied.

Signed-off-by: David Howells