linux.git/fs/cachefiles/rdwr.c, branch v5.8

cachefiles: switch to kernel_write

2020-07-08T06:27:56+00:00

__kernel_write doesn't take a sb_writers references, which we need here.

Signed-off-by: Christoph Hellwig 
Reviewed-by: David Howells

cachefiles: Fix race between read_waiter and read_copier involving op->to_do

2020-05-08T22:01:10+00:00

There is a potential race in fscache operation enqueuing for reading and
copying multiple pages from cachefiles to netfs.  The problem can be seen
easily on a heavy loaded system (for example many processes reading files
continually on an NFS share covered by fscache triggered this problem within
a few minutes).

The race is due to cachefiles_read_waiter() adding the op to the monitor
to_do list and then then drop the object->work_lock spinlock before
completing fscache_enqueue_operation().  Once the lock is dropped,
cachefiles_read_copier() grabs the op, completes processing it, and
makes it through fscache_retrieval_complete() which sets the op->state to
the final state of FSCACHE_OP_ST_COMPLETE(4).  When cachefiles_read_waiter()
finally gets through the remainder of fscache_enqueue_operation()
it sees the invalid state, and hits the ASSERTCMP and the following
oops is seen:
[ 2259.612361] FS-Cache:
[ 2259.614785] FS-Cache: Assertion failed
[ 2259.618639] FS-Cache: 4 == 5 is false
[ 2259.622456] ------------[ cut here ]------------
[ 2259.627190] kernel BUG at fs/fscache/operation.c:70!
...
[ 2259.791675] RIP: 0010:[]  [] fscache_enqueue_operation+0xff/0x170 [fscache]
[ 2259.802059] RSP: 0000:ffffa0263d543be0  EFLAGS: 00010046
[ 2259.807521] RAX: 0000000000000019 RBX: ffffa01a4d390480 RCX: 0000000000000006
[ 2259.814847] RDX: 0000000000000000 RSI: 0000000000000046 RDI: ffffa0263d553890
[ 2259.822176] RBP: ffffa0263d543be8 R08: 0000000000000000 R09: ffffa0263c2d8708
[ 2259.829502] R10: 0000000000001e7f R11: 0000000000000000 R12: ffffa01a4d390480
[ 2259.844483] R13: ffff9fa9546c5920 R14: ffffa0263d543c80 R15: ffffa0293ff9bf10
[ 2259.859554] FS:  00007f4b6efbd700(0000) GS:ffffa0263d540000(0000) knlGS:0000000000000000
[ 2259.875571] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2259.889117] CR2: 00007f49e1624ff0 CR3: 0000012b38b38000 CR4: 00000000007607e0
[ 2259.904015] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 2259.918764] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 2259.933449] PKRU: 55555554
[ 2259.943654] Call Trace:
[ 2259.953592]  
[ 2259.955577]  [] cachefiles_read_waiter+0x92/0xf0 [cachefiles]
[ 2259.978039]  [] __wake_up_common+0x82/0x120
[ 2259.991392]  [] __wake_up_common_lock+0x83/0xc0
[ 2260.004930]  [] ? task_rq_unlock+0x20/0x20
[ 2260.017863]  [] __wake_up+0x13/0x20
[ 2260.030230]  [] __wake_up_bit+0x50/0x70
[ 2260.042535]  [] unlock_page+0x2b/0x30
[ 2260.054495]  [] page_endio+0x29/0x90
[ 2260.066184]  [] mpage_end_io+0x51/0x80

CPU1
cachefiles_read_waiter()
 20 static int cachefiles_read_waiter(wait_queue_entry_t *wait, unsigned mode,
 21                                   int sync, void *_key)
 22 {
...
 61         spin_lock(&object->work_lock);
 62         list_add_tail(&monitor->op_link, &op->to_do);
 63         spin_unlock(&object->work_lock);

 64
 65         fscache_enqueue_retrieval(op);
182 static inline void fscache_enqueue_retrieval(struct fscache_retrieval *op)
183 {
184         fscache_enqueue_operation(&op->op);
185 }
 58 void fscache_enqueue_operation(struct fscache_operation *op)
 59 {
 60         struct fscache_cookie *cookie = op->object->cookie;
 61
 62         _enter("{OBJ%x OP%x,%u}",
 63                op->object->debug_id, op->debug_id, atomic_read(&op->usage));
 64
 65         ASSERT(list_empty(&op->pend_link));
 66         ASSERT(op->processor != NULL);
 67         ASSERT(fscache_object_is_available(op->object));
 68         ASSERTCMP(atomic_read(&op->usage), >, 0);


CPU2
cachefiles_read_copier()
168         while (!list_empty(&op->to_do)) {
...
202                 fscache_end_io(op, monitor->netfs_page, error);
203                 put_page(monitor->netfs_page);
204                 fscache_retrieval_complete(op, 1);

CPU1
 58 void fscache_enqueue_operation(struct fscache_operation *op)
 59 {
...
 69         ASSERTIFCMP(op->state != FSCACHE_OP_ST_IN_PROGRESS,
 70                     op->state, ==,  FSCACHE_OP_ST_CANCELLED);

Signed-off-by: Lei Xue 
Signed-off-by: Dave Wysochanski 
Signed-off-by: David Howells

cachefiles: Fix corruption of the return value in cachefiles_read_or_alloc_pages()

2020-05-04T15:20:13+00:00

The patch which changed cachefiles from calling ->bmap() to using the
bmap() wrapper overwrote the running return value with the result of
calling bmap().  This causes an assertion failure elsewhere in the code.

Fix this by using ret2 rather than ret to hold the return value.

The oops looks like:

	kernel BUG at fs/nfs/fscache.c:468!
	...
	RIP: 0010:__nfs_readpages_from_fscache+0x18b/0x190 [nfs]
	...
	Call Trace:
	 nfs_readpages+0xbf/0x1c0 [nfs]
	 ? __alloc_pages_nodemask+0x16c/0x320
	 read_pages+0x67/0x1a0
	 __do_page_cache_readahead+0x1cf/0x1f0
	 ondemand_readahead+0x172/0x2b0
	 page_cache_async_readahead+0xaa/0xe0
	 generic_file_buffered_read+0x852/0xd50
	 ? mem_cgroup_commit_charge+0x6e/0x140
	 ? nfs4_have_delegation+0x19/0x30 [nfsv4]
	 generic_file_read_iter+0x100/0x140
	 ? nfs_revalidate_mapping+0x176/0x2b0 [nfs]
	 nfs_file_read+0x6d/0xc0 [nfs]
	 new_sync_read+0x11a/0x1c0
	 __vfs_read+0x29/0x40
	 vfs_read+0x8e/0x140
	 ksys_read+0x61/0xd0
	 __x64_sys_read+0x1a/0x20
	 do_syscall_64+0x60/0x1e0
	 entry_SYSCALL_64_after_hwframe+0x44/0xa9
	RIP: 0033:0x7f5d148267e0

Fixes: 10d83e11a582 ("cachefiles: drop direct usage of ->bmap method.")
Reported-by: David Wysochanski 
Signed-off-by: David Howells 
Tested-by: David Wysochanski 
cc: Carlos Maiolino

cachefiles: drop direct usage of ->bmap method.

2020-02-03T13:05:56+00:00

Replace the direct usage of ->bmap method by a bmap() call.

Reviewed-by: Christoph Hellwig 
Signed-off-by: Carlos Maiolino 
Signed-off-by: Al Viro

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 36

2019-05-24T15:27:11+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 licence as published by
  the free software foundation either version 2 of the licence 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 114 file(s).

Signed-off-by: Thomas Gleixner 
Reviewed-by: Allison Randal 
Reviewed-by: Kate Stewart 
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190520170857.552531963@linutronix.de
Signed-off-by: Greg Kroah-Hartman

fscache, cachefiles: remove redundant variable 'cache'

2018-11-30T16:00:58+00:00

Variable 'cache' is being assigned but is never used hence it is
redundant and can be removed.

Cleans up clang warning:
warning: variable 'cache' set but not used [-Wunused-but-set-variable]

Signed-off-by: Colin Ian King 
Signed-off-by: David Howells

cachefiles: Fix page leak in cachefiles_read_backing_file while vmscan is active

2018-11-28T14:47:05+00:00

[Description]

In a heavily loaded system where the system pagecache is nearing memory
limits and fscache is enabled, pages can be leaked by fscache while trying
read pages from cachefiles backend.  This can happen because two
applications can be reading same page from a single mount, two threads can
be trying to read the backing page at same time.  This results in one of
the threads finding that a page for the backing file or netfs file is
already in the radix tree.  During the error handling cachefiles does not
clean up the reference on backing page, leading to page leak.

[Fix]
The fix is straightforward, to decrement the reference when error is
encountered.

  [dhowells: Note that I've removed the clearance and put of newpage as
   they aren't attested in the commit message and don't appear to actually
   achieve anything since a new page is only allocated is newpage!=NULL and
   any residual new page is cleared before returning.]

[Testing]
I have tested the fix using following method for 12+ hrs.

1) mkdir -p /mnt/nfs ; mount -o vers=3,fsc :/export /mnt/nfs
2) create 10000 files of 2.8MB in a NFS mount.
3) start a thread to simulate heavy VM presssure
   (while true ; do echo 3 > /proc/sys/vm/drop_caches ; sleep 1 ; done)&
4) start multiple parallel reader for data set at same time
   find /mnt/nfs -type f | xargs -P 80 cat > /dev/null &
   find /mnt/nfs -type f | xargs -P 80 cat > /dev/null &
   find /mnt/nfs -type f | xargs -P 80 cat > /dev/null &
   ..
   ..
   find /mnt/nfs -type f | xargs -P 80 cat > /dev/null &
   find /mnt/nfs -type f | xargs -P 80 cat > /dev/null &
5) finally check using cat /proc/fs/fscache/stats | grep -i pages ;
   free -h , cat /proc/meminfo and page-types -r -b lru
   to ensure all pages are freed.

Reviewed-by: Daniel Axtens 
Signed-off-by: Shantanu Goel 
Signed-off-by: Kiran Kumar Modukuri 
[dja: forward ported to current upstream]
Signed-off-by: Daniel Axtens 
Signed-off-by: David Howells

cachefiles: Fix refcounting bug in backing-file read monitoring

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

cachefiles_read_waiter() has the right to access a 'monitor' object by
virtue of being called under the waitqueue lock for one of the pages in its
purview.  However, it has no ref on that monitor object or on the
associated operation.

What it is allowed to do is to move the monitor object to the operation's
to_do list, but once it drops the work_lock, it's actually no longer
permitted to access that object.  However, it is trying to enqueue the
retrieval operation for processing - but it can only do this via a pointer
in the monitor object, something it shouldn't be doing.

If it doesn't enqueue the operation, the operation may not get processed.
If the order is flipped so that the enqueue is first, then it's possible
for the work processor to look at the to_do list before the monitor is
enqueued upon it.

Fix this by getting a ref on the operation so that we can trust that it
will still be there once we've added the monitor to the to_do list and
dropped the work_lock.  The op can then be enqueued after the lock is
dropped.

The bug can manifest in one of a couple of ways.  The first manifestation
looks like:

 FS-Cache:
 FS-Cache: Assertion failed
 FS-Cache: 6 == 5 is false
 ------------[ cut here ]------------
 kernel BUG at fs/fscache/operation.c:494!
 RIP: 0010:fscache_put_operation+0x1e3/0x1f0
 ...
 fscache_op_work_func+0x26/0x50
 process_one_work+0x131/0x290
 worker_thread+0x45/0x360
 kthread+0xf8/0x130
 ? create_worker+0x190/0x190
 ? kthread_cancel_work_sync+0x10/0x10
 ret_from_fork+0x1f/0x30

This is due to the operation being in the DEAD state (6) rather than
INITIALISED, COMPLETE or CANCELLED (5) because it's already passed through
fscache_put_operation().

The bug can also manifest like the following:

 kernel BUG at fs/fscache/operation.c:69!
 ...
    [exception RIP: fscache_enqueue_operation+246]
 ...
 #7 [ffff883fff083c10] fscache_enqueue_operation at ffffffffa0b793c6
 #8 [ffff883fff083c28] cachefiles_read_waiter at ffffffffa0b15a48
 #9 [ffff883fff083c48] __wake_up_common at ffffffff810af028

I'm not entirely certain as to which is line 69 in Lei's kernel, so I'm not
entirely clear which assertion failed.

Fixes: 9ae326a69004 ("CacheFiles: A cache that backs onto a mounted filesystem")
Reported-by: Lei Xue 
Reported-by: Vegard Nossum 
Reported-by: Anthony DeRobertis 
Reported-by: NeilBrown 
Reported-by: Daniel Axtens 
Reported-by: Kiran Kumar Modukuri 
Signed-off-by: David Howells 
Reviewed-by: Daniel Axtens

fscache, cachefiles: Fix checker warnings

2018-04-04T12:41:26+00:00

Fix a couple of checker warnings in fscache and cachefiles:

 (1) fscache_n_op_requeue is never used, so get rid of it.

 (2) cachefiles_uncache_page() is passed in a lock that it releases, so
     this needs annotating.

Signed-off-by: David Howells

mm: remove __GFP_COLD

2017-11-16T02:21:06+00:00

As the page free path makes no distinction between cache hot and cold
pages, there is no real useful ordering of pages in the free list that
allocation requests can take advantage of.  Juding from the users of
__GFP_COLD, it is likely that a number of them are the result of copying
other sites instead of actually measuring the impact.  Remove the
__GFP_COLD parameter which simplifies a number of paths in the page
allocator.

This is potentially controversial but bear in mind that the size of the
per-cpu pagelists versus modern cache sizes means that the whole per-cpu
list can often fit in the L3 cache.  Hence, there is only a potential
benefit for microbenchmarks that alloc/free pages in a tight loop.  It's
even worse when THP is taken into account which has little or no chance
of getting a cache-hot page as the per-cpu list is bypassed and the
zeroing of multiple pages will thrash the cache anyway.

The truncate microbenchmarks are not shown as this patch affects the
allocation path and not the free path.  A page fault microbenchmark was
tested but it showed no sigificant difference which is not surprising
given that the __GFP_COLD branches are a miniscule percentage of the
fault path.

Link: http://lkml.kernel.org/r/20171018075952.10627-9-mgorman@techsingularity.net
Signed-off-by: Mel Gorman 
Acked-by: Vlastimil Babka 
Cc: Andi Kleen 
Cc: Dave Chinner 
Cc: Dave Hansen 
Cc: Jan Kara 
Cc: Johannes Weiner 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds