linux.git/fs/fscache, branch v4.18

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: Allow cancelled operations to be enqueued

2018-07-25T13:31:20+00:00

Alter the state-check assertion in fscache_enqueue_operation() to allow
cancelled operations to be given processing time so they can be cleaned up.

Also fix a debugging statement that was requiring such operations to have
an object assigned.

Fixes: 9ae326a69004 ("CacheFiles: A cache that backs onto a mounted filesystem")
Reported-by: Kiran Kumar Modukuri 
Signed-off-by: David Howells

proc: introduce proc_create_single{,_data}

2018-05-16T05:23:35+00:00

Variants of proc_create{,_data} that directly take a seq_file show
callback and drastically reduces the boilerplate code in the callers.

All trivial callers converted over.

Signed-off-by: Christoph Hellwig

proc: introduce proc_create_seq{,_data}

2018-05-16T05:23:35+00:00

Variants of proc_create{,_data} that directly take a struct seq_operations
argument and drastically reduces the boilerplate code in the callers.

All trivial callers converted over.

Signed-off-by: Christoph Hellwig

fscache: use appropriate radix tree accessors

2018-04-11T17:28:39+00:00

Don't open-code accesses to data structure internals.

Link: http://lkml.kernel.org/r/20180313132639.17387-7-willy@infradead.org
Signed-off-by: Matthew Wilcox 
Reviewed-by: Jeff Layton 
Cc: Darrick J. Wong 
Cc: Dave Chinner 
Cc: Ryusuke Konishi 
Cc: Will Deacon 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fscache: Maintain a catalogue of allocated cookies

2018-04-06T13:05:14+00:00

Maintain a catalogue of allocated cookies so that cookie collisions can be
handled properly.  For the moment, this just involves printing a warning
and returning a NULL cookie to the caller of fscache_acquire_cookie(), but
in future it might make sense to wait for the old cookie to finish being
cleaned up.

This requires the cookie key to be stored attached to the cookie so that we
still have the key available if the netfs relinquishes the cookie.  This is
done by an earlier patch.

The catalogue also renders redundant fscache_netfs_list (used for checking
for duplicates), so that can be removed.

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

fscache: Pass object size in rather than calling back for it

2018-04-06T13:05:14+00:00

Pass the object size in to fscache_acquire_cookie() and
fscache_write_page() rather than the netfs providing a callback by which it
can be received.  This makes it easier to update the size of the object
when a new page is written that extends the object.

The current object size is also passed by fscache to the check_aux
function, obviating the need to store it in the aux data.

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

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

fscache: Add more tracepoints

2018-04-04T12:41:27+00:00

Add more tracepoints to fscache, including:

 (*) fscache_page - Tracks netfs pages known to fscache.

 (*) fscache_check_page - Tracks the netfs querying whether a page is
     pending storage.

 (*) fscache_wake_cookie - Tracks cookies being woken up after a page
     completes/aborts storage in the cache.

 (*) fscache_op - Tracks operations being initialised.

 (*) fscache_wrote_page - Tracks return of the backend write_page op.

 (*) fscache_gang_lookup - Tracks lookup of pages to be stored in the write
     operation.

Signed-off-by: David Howells

fscache: Add tracepoints

2018-04-04T12:41:27+00:00

Add some tracepoints to fscache:

 (*) fscache_cookie - Tracks a cookie's usage count.

 (*) fscache_netfs - Logs registration of a network filesystem, including
     the pointer to the cookie allocated.

 (*) fscache_acquire - Logs cookie acquisition.

 (*) fscache_relinquish - Logs cookie relinquishment.

 (*) fscache_enable - Logs enablement of a cookie.

 (*) fscache_disable - Logs disablement of a cookie.

 (*) fscache_osm - Tracks execution of states in the object state machine.

and cachefiles:

 (*) cachefiles_ref - Tracks a cachefiles object's usage count.

 (*) cachefiles_lookup - Logs result of lookup_one_len().

 (*) cachefiles_mkdir - Logs result of vfs_mkdir().

 (*) cachefiles_create - Logs result of vfs_create().

 (*) cachefiles_unlink - Logs calls to vfs_unlink().

 (*) cachefiles_rename - Logs calls to vfs_rename().

 (*) cachefiles_mark_active - Logs an object becoming active.

 (*) cachefiles_wait_active - Logs a wait for an old object to be
     destroyed.

 (*) cachefiles_mark_inactive - Logs an object becoming inactive.

 (*) cachefiles_mark_buried - Logs the burial of an object.

Signed-off-by: David Howells