path: root/Documentation
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authorDavid Howells <dhowells@redhat.com>2012-12-20 21:52:35 +0000
committerDavid Howells <dhowells@redhat.com>2012-12-20 21:58:26 +0000
commit9f10523f891928330b7529da54c1a3cc65180b1a (patch)
tree014731e89d44d1ca86cc665f4d39d8d2c25c69bf /Documentation
parentef46ed888efb1e8da33be5d33c9b54476289a43b (diff)
FS-Cache: Fix operation state management and accounting
Fix the state management of internal fscache operations and the accounting of what operations are in what states. This is done by: (1) Give struct fscache_operation a enum variable that directly represents the state it's currently in, rather than spreading this knowledge over a bunch of flags, who's processing the operation at the moment and whether it is queued or not. This makes it easier to write assertions to check the state at various points and to prevent invalid state transitions. (2) Add an 'operation complete' state and supply a function to indicate the completion of an operation (fscache_op_complete()) and make things call it. The final call to fscache_put_operation() can then check that an op in the appropriate state (complete or cancelled). (3) Adjust the use of object->n_ops, ->n_in_progress, ->n_exclusive to better govern the state of an object: (a) The ->n_ops is now the number of extant operations on the object and is now decremented by fscache_put_operation() only. (b) The ->n_in_progress is simply the number of objects that have been taken off of the object's pending queue for the purposes of being run. This is decremented by fscache_op_complete() only. (c) The ->n_exclusive is the number of exclusive ops that have been submitted and queued or are in progress. It is decremented by fscache_op_complete() and by fscache_cancel_op(). fscache_put_operation() and fscache_operation_gc() now no longer try to clean up ->n_exclusive and ->n_in_progress. That was leading to double decrements against fscache_cancel_op(). fscache_cancel_op() now no longer decrements ->n_ops. That was leading to double decrements against fscache_put_operation(). fscache_submit_exclusive_op() now decides whether it has to queue an op based on ->n_in_progress being > 0 rather than ->n_ops > 0 as the latter will persist in being true even after all preceding operations have been cancelled or completed. Furthermore, if an object is active and there are runnable ops against it, there must be at least one op running. (4) Add a remaining-pages counter (n_pages) to struct fscache_retrieval and provide a function to record completion of the pages as they complete. When n_pages reaches 0, the operation is deemed to be complete and fscache_op_complete() is called. Add calls to fscache_retrieval_complete() anywhere we've finished with a page we've been given to read or allocate for. This includes places where we just return pages to the netfs for reading from the server and where accessing the cache fails and we discard the proposed netfs page. The bugs in the unfixed state management manifest themselves as oopses like the following where the operation completion gets out of sync with return of the cookie by the netfs. This is possible because the cache unlocks and returns all the netfs pages before recording its completion - which means that there's nothing to stop the netfs discarding them and returning the cookie. FS-Cache: Cookie 'NFS.fh' still has outstanding reads ------------[ cut here ]------------ kernel BUG at fs/fscache/cookie.c:519! invalid opcode: 0000 [#1] SMP CPU 1 Modules linked in: cachefiles nfs fscache auth_rpcgss nfs_acl lockd sunrpc Pid: 400, comm: kswapd0 Not tainted 3.1.0-rc7-fsdevel+ #1090 /DG965RY RIP: 0010:[<ffffffffa007050a>] [<ffffffffa007050a>] __fscache_relinquish_cookie+0x170/0x343 [fscache] RSP: 0018:ffff8800368cfb00 EFLAGS: 00010282 RAX: 000000000000003c RBX: ffff880023cc8790 RCX: 0000000000000000 RDX: 0000000000002f2e RSI: 0000000000000001 RDI: ffffffff813ab86c RBP: ffff8800368cfb50 R08: 0000000000000002 R09: 0000000000000000 R10: ffff88003a1b7890 R11: ffff88001df6e488 R12: ffff880023d8ed98 R13: ffff880023cc8798 R14: 0000000000000004 R15: ffff88003b8bf370 FS: 0000000000000000(0000) GS:ffff88003bd00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: 00000000008ba008 CR3: 0000000023d93000 CR4: 00000000000006e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Process kswapd0 (pid: 400, threadinfo ffff8800368ce000, task ffff88003b8bf040) Stack: ffff88003b8bf040 ffff88001df6e528 ffff88001df6e528 ffffffffa00b46b0 ffff88003b8bf040 ffff88001df6e488 ffff88001df6e620 ffffffffa00b46b0 ffff88001ebd04c8 0000000000000004 ffff8800368cfb70 ffffffffa00b2c91 Call Trace: [<ffffffffa00b2c91>] nfs_fscache_release_inode_cookie+0x3b/0x47 [nfs] [<ffffffffa008f25f>] nfs_clear_inode+0x3c/0x41 [nfs] [<ffffffffa0090df1>] nfs4_evict_inode+0x2f/0x33 [nfs] [<ffffffff810d8d47>] evict+0xa1/0x15c [<ffffffff810d8e2e>] dispose_list+0x2c/0x38 [<ffffffff810d9ebd>] prune_icache_sb+0x28c/0x29b [<ffffffff810c56b7>] prune_super+0xd5/0x140 [<ffffffff8109b615>] shrink_slab+0x102/0x1ab [<ffffffff8109d690>] balance_pgdat+0x2f2/0x595 [<ffffffff8103e009>] ? process_timeout+0xb/0xb [<ffffffff8109dba3>] kswapd+0x270/0x289 [<ffffffff8104c5ea>] ? __init_waitqueue_head+0x46/0x46 [<ffffffff8109d933>] ? balance_pgdat+0x595/0x595 [<ffffffff8104bf7a>] kthread+0x7f/0x87 [<ffffffff813ad6b4>] kernel_thread_helper+0x4/0x10 [<ffffffff81026b98>] ? finish_task_switch+0x45/0xc0 [<ffffffff813abcdd>] ? retint_restore_args+0xe/0xe [<ffffffff8104befb>] ? __init_kthread_worker+0x53/0x53 [<ffffffff813ad6b0>] ? gs_change+0xb/0xb Signed-off-by: David Howells <dhowells@redhat.com>
Diffstat (limited to 'Documentation')
2 files changed, 26 insertions, 2 deletions
diff --git a/Documentation/filesystems/caching/backend-api.txt b/Documentation/filesystems/caching/backend-api.txt
index 382d52cdaf2..f4769b9399d 100644
--- a/Documentation/filesystems/caching/backend-api.txt
+++ b/Documentation/filesystems/caching/backend-api.txt
@@ -419,7 +419,10 @@ performed on the denizens of the cache. These are held in a structure of type:
If an I/O error occurs, fscache_io_error() should be called and -ENOBUFS
returned if possible or fscache_end_io() called with a suitable error
- code..
+ code.
+ fscache_put_retrieval() should be called after a page or pages are dealt
+ with. This will complete the operation when all pages are dealt with.
(*) Request pages be read from cache [mandatory]:
@@ -526,6 +529,27 @@ FS-Cache provides some utilities that a cache backend may make use of:
error value should be 0 if successful and an error otherwise.
+ (*) Record that one or more pages being retrieved or allocated have been dealt
+ with:
+ void fscache_retrieval_complete(struct fscache_retrieval *op,
+ int n_pages);
+ This is called to record the fact that one or more pages have been dealt
+ with and are no longer the concern of this operation. When the number of
+ pages remaining in the operation reaches 0, the operation will be
+ completed.
+ (*) Record operation completion:
+ void fscache_op_complete(struct fscache_operation *op);
+ This is called to record the completion of an operation. This deducts
+ this operation from the parent object's run state, potentially permitting
+ one or more pending operations to start running.
(*) Set highest store limit:
void fscache_set_store_limit(struct fscache_object *object,
diff --git a/Documentation/filesystems/caching/operations.txt b/Documentation/filesystems/caching/operations.txt
index b6b070c57cb..bee2a5f93d6 100644
--- a/Documentation/filesystems/caching/operations.txt
+++ b/Documentation/filesystems/caching/operations.txt
@@ -174,7 +174,7 @@ Operations are used through the following procedure:
necessary (the object might have died whilst the thread was waiting).
When it has finished doing its processing, it should call
- fscache_put_operation() on it.
+ fscache_op_complete() and fscache_put_operation() on it.
(4) The operation holds an effective lock upon the object, preventing other
exclusive ops conflicting until it is released. The operation can be