linux-stable.git/fs/file.c, branch v4.9.321 Linux kernel stable tree fget: clarify and improve __fget_files() implementation 2022-03-02T10:32:07+00:00 Linus Torvalds torvalds@linux-foundation.org 2022-02-26T06:33:24+00:00 1ebb62c91086f4d6b7ce2ff69e9d0e99006fbf5c commit e386dfc56f837da66d00a078e5314bc8382fab83 upstream. Commit 054aa8d439b9 ("fget: check that the fd still exists after getting a ref to it") fixed a race with getting a reference to a file just as it was being closed. It was a fairly minimal patch, and I didn't think re-checking the file pointer lookup would be a measurable overhead, since it was all right there and cached. But I was wrong, as pointed out by the kernel test robot. The 'poll2' case of the will-it-scale.per_thread_ops benchmark regressed quite noticeably. Admittedly it seems to be a very artificial test: doing "poll()" system calls on regular files in a very tight loop in multiple threads. That means that basically all the time is spent just looking up file descriptors without ever doing anything useful with them (not that doing 'poll()' on a regular file is useful to begin with). And as a result it shows the extra "re-check fd" cost as a sore thumb. Happily, the regression is fixable by just writing the code to loook up the fd to be better and clearer. There's still a cost to verify the file pointer, but now it's basically in the noise even for that benchmark that does nothing else - and the code is more understandable and has better comments too. [ Side note: this patch is also a classic case of one that looks very messy with the default greedy Myers diff - it's much more legible with either the patience of histogram diff algorithm ] Link: https://lore.kernel.org/lkml/20211210053743.GA36420@xsang-OptiPlex-9020/ Link: https://lore.kernel.org/lkml/20211213083154.GA20853@linux.intel.com/ Reported-by: kernel test robot <oliver.sang@intel.com> Tested-by: Carel Si <beibei.si@intel.com> Cc: Jann Horn <jannh@google.com> Cc: Miklos Szeredi <mszeredi@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Baokun Li <libaokun1@huawei.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit e386dfc56f837da66d00a078e5314bc8382fab83 upstream.

Commit 054aa8d439b9 ("fget: check that the fd still exists after getting
a ref to it") fixed a race with getting a reference to a file just as it
was being closed.  It was a fairly minimal patch, and I didn't think
re-checking the file pointer lookup would be a measurable overhead,
since it was all right there and cached.

But I was wrong, as pointed out by the kernel test robot.

The 'poll2' case of the will-it-scale.per_thread_ops benchmark regressed
quite noticeably.  Admittedly it seems to be a very artificial test:
doing "poll()" system calls on regular files in a very tight loop in
multiple threads.

That means that basically all the time is spent just looking up file
descriptors without ever doing anything useful with them (not that doing
'poll()' on a regular file is useful to begin with).  And as a result it
shows the extra "re-check fd" cost as a sore thumb.

Happily, the regression is fixable by just writing the code to loook up
the fd to be better and clearer.  There's still a cost to verify the
file pointer, but now it's basically in the noise even for that
benchmark that does nothing else - and the code is more understandable
and has better comments too.

[ Side note: this patch is also a classic case of one that looks very
  messy with the default greedy Myers diff - it's much more legible with
  either the patience of histogram diff algorithm ]

Link: https://lore.kernel.org/lkml/20211210053743.GA36420@xsang-OptiPlex-9020/
Link: https://lore.kernel.org/lkml/20211213083154.GA20853@linux.intel.com/
Reported-by: kernel test robot <oliver.sang@intel.com>
Tested-by: Carel Si <beibei.si@intel.com>
Cc: Jann Horn <jannh@google.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
fget: check that the fd still exists after getting a ref to it 2021-12-08T07:45:06+00:00 Linus Torvalds torvalds@linux-foundation.org 2021-12-01T18:06:14+00:00 a043f5a600052dc93bc3d7a6a2c1592b6ee77482 commit 054aa8d439b9185d4f5eb9a90282d1ce74772969 upstream. Jann Horn points out that there is another possible race wrt Unix domain socket garbage collection, somewhat reminiscent of the one fixed in commit cbcf01128d0a ("af_unix: fix garbage collect vs MSG_PEEK"). See the extended comment about the garbage collection requirements added to unix_peek_fds() by that commit for details. The race comes from how we can locklessly look up a file descriptor just as it is in the process of being closed, and with the right artificial timing (Jann added a few strategic 'mdelay(500)' calls to do that), the Unix domain socket garbage collector could see the reference count decrement of the close() happen before fget() took its reference to the file and the file was attached onto a new file descriptor. This is all (intentionally) correct on the 'struct file *' side, with RCU lookups and lockless reference counting very much part of the design. Getting that reference count out of order isn't a problem per se. But the garbage collector can get confused by seeing this situation of having seen a file not having any remaining external references and then seeing it being attached to an fd. In commit cbcf01128d0a ("af_unix: fix garbage collect vs MSG_PEEK") the fix was to serialize the file descriptor install with the garbage collector by taking and releasing the unix_gc_lock. That's not really an option here, but since this all happens when we are in the process of looking up a file descriptor, we can instead simply just re-check that the file hasn't been closed in the meantime, and just re-do the lookup if we raced with a concurrent close() of the same file descriptor. Reported-and-tested-by: Jann Horn <jannh@google.com> Acked-by: Miklos Szeredi <mszeredi@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 054aa8d439b9185d4f5eb9a90282d1ce74772969 upstream.

Jann Horn points out that there is another possible race wrt Unix domain
socket garbage collection, somewhat reminiscent of the one fixed in
commit cbcf01128d0a ("af_unix: fix garbage collect vs MSG_PEEK").

See the extended comment about the garbage collection requirements added
to unix_peek_fds() by that commit for details.

The race comes from how we can locklessly look up a file descriptor just
as it is in the process of being closed, and with the right artificial
timing (Jann added a few strategic 'mdelay(500)' calls to do that), the
Unix domain socket garbage collector could see the reference count
decrement of the close() happen before fget() took its reference to the
file and the file was attached onto a new file descriptor.

This is all (intentionally) correct on the 'struct file *' side, with
RCU lookups and lockless reference counting very much part of the
design.  Getting that reference count out of order isn't a problem per
se.

But the garbage collector can get confused by seeing this situation of
having seen a file not having any remaining external references and then
seeing it being attached to an fd.

In commit cbcf01128d0a ("af_unix: fix garbage collect vs MSG_PEEK") the
fix was to serialize the file descriptor install with the garbage
collector by taking and releasing the unix_gc_lock.

That's not really an option here, but since this all happens when we are
in the process of looking up a file descriptor, we can instead simply
just re-check that the file hasn't been closed in the meantime, and just
re-do the lookup if we raced with a concurrent close() of the same file
descriptor.

Reported-and-tested-by: Jann Horn <jannh@google.com>
Acked-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
fs: add fget_many() and fput_many() 2021-12-08T07:45:06+00:00 Jens Axboe axboe@kernel.dk 2018-11-21T17:32:39+00:00 0917c0b01f27bf4101c5716884861e7bd94d26c8 commit 091141a42e15fe47ada737f3996b317072afcefb upstream. Some uses cases repeatedly get and put references to the same file, but the only exposed interface is doing these one at the time. As each of these entail an atomic inc or dec on a shared structure, that cost can add up. Add fget_many(), which works just like fget(), except it takes an argument for how many references to get on the file. Ditto fput_many(), which can drop an arbitrary number of references to a file. Reviewed-by: Hannes Reinecke <hare@suse.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 091141a42e15fe47ada737f3996b317072afcefb upstream.

Some uses cases repeatedly get and put references to the same file, but
the only exposed interface is doing these one at the time. As each of
these entail an atomic inc or dec on a shared structure, that cost can
add up.

Add fget_many(), which works just like fget(), except it takes an
argument for how many references to get on the file. Ditto fput_many(),
which can drop an arbitrary number of references to a file.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
fix multiplication overflow in copy_fdtable() 2020-05-27T14:41:40+00:00 Al Viro viro@zeniv.linux.org.uk 2020-05-19T21:48:52+00:00 26204c47c87966ec458258a74555bc11ce6fca68 [ Upstream commit 4e89b7210403fa4a8acafe7c602b6212b7af6c3b ] cpy and set really should be size_t; we won't get an overflow on that, since sysctl_nr_open can't be set above ~(size_t)0 / sizeof(void *), so nr that would've managed to overflow size_t on that multiplication won't get anywhere near copy_fdtable() - we'll fail with EMFILE before that. Cc: stable@kernel.org # v2.6.25+ Fixes: 9cfe015aa424 (get rid of NR_OPEN and introduce a sysctl_nr_open) Reported-by: Thiago Macieira <thiago.macieira@intel.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 4e89b7210403fa4a8acafe7c602b6212b7af6c3b ]

cpy and set really should be size_t; we won't get an overflow on that,
since sysctl_nr_open can't be set above ~(size_t)0 / sizeof(void *),
so nr that would've managed to overflow size_t on that multiplication
won't get anywhere near copy_fdtable() - we'll fail with EMFILE
before that.

Cc: stable@kernel.org # v2.6.25+
Fixes: 9cfe015aa424 (get rid of NR_OPEN and introduce a sysctl_nr_open)
Reported-by: Thiago Macieira <thiago.macieira@intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
fs/file.c: initialize init_files.resize_wait 2019-04-05T20:29:07+00:00 Shuriyc Chu sureeju@gmail.com 2019-03-05T23:41:56+00:00 7368f9244c9de2b63d3a37e22f790a572c20e43a [ Upstream commit 5704a06810682683355624923547b41540e2801a ] (Taken from https://bugzilla.kernel.org/show_bug.cgi?id=200647) 'get_unused_fd_flags' in kthread cause kernel crash. It works fine on 4.1, but causes crash after get 64 fds. It also cause crash on ubuntu1404/1604/1804, centos7.5, and the crash messages are almost the same. The crash message on centos7.5 shows below: start fd 61 start fd 62 start fd 63 BUG: unable to handle kernel NULL pointer dereference at (null) IP: __wake_up_common+0x2e/0x90 PGD 0 Oops: 0000 [#1] SMP Modules linked in: test(OE) xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ipt_REJECT nf_reject_ipv4 tun bridge stp llc ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter devlink sunrpc kvm_intel kvm irqbypass crc32_pclmul ghash_clmulni_intel aesni_intel lrw gf128mul glue_helper ablk_helper cryptd sg ppdev pcspkr virtio_balloon parport_pc parport i2c_piix4 joydev ip_tables xfs libcrc32c sr_mod cdrom sd_mod crc_t10dif crct10dif_generic ata_generic pata_acpi virtio_scsi virtio_console virtio_net cirrus drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ttm crct10dif_pclmul crct10dif_common crc32c_intel drm ata_piix serio_raw libata virtio_pci virtio_ring i2c_core virtio floppy dm_mirror dm_region_hash dm_log dm_mod CPU: 2 PID: 1820 Comm: test_fd Kdump: loaded Tainted: G OE ------------ 3.10.0-862.3.3.el7.x86_64 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.10.2-0-g5f4c7b1-prebuilt.qemu-project.org 04/01/2014 task: ffff8e92b9431fa0 ti: ffff8e94247a0000 task.ti: ffff8e94247a0000 RIP: 0010:__wake_up_common+0x2e/0x90 RSP: 0018:ffff8e94247a2d18 EFLAGS: 00010086 RAX: 0000000000000000 RBX: ffffffff9d09daa0 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffffffff9d09daa0 RBP: ffff8e94247a2d50 R08: 0000000000000000 R09: ffff8e92b95dfda8 R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff9d09daa8 R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000003 FS: 0000000000000000(0000) GS:ffff8e9434e80000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000000 CR3: 000000017c686000 CR4: 00000000000207e0 Call Trace: __wake_up+0x39/0x50 expand_files+0x131/0x250 __alloc_fd+0x47/0x170 get_unused_fd_flags+0x30/0x40 test_fd+0x12a/0x1c0 [test] kthread+0xd1/0xe0 ret_from_fork_nospec_begin+0x21/0x21 Code: 66 90 55 48 89 e5 41 57 41 89 f7 41 56 41 89 ce 41 55 41 54 49 89 fc 49 83 c4 08 53 48 83 ec 10 48 8b 47 08 89 55 cc 4c 89 45 d0 <48> 8b 08 49 39 c4 48 8d 78 e8 4c 8d 69 e8 75 08 eb 3b 4c 89 ef RIP __wake_up_common+0x2e/0x90 RSP <ffff8e94247a2d18> CR2: 0000000000000000 This issue exists since CentOS 7.5 3.10.0-862 and CentOS 7.4 (3.10.0-693.21.1 ) is ok. Root cause: the item 'resize_wait' is not initialized before being used. Reported-by: Richard Zhang <zhang.zijian@h3c.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 5704a06810682683355624923547b41540e2801a ]

(Taken from https://bugzilla.kernel.org/show_bug.cgi?id=200647)

'get_unused_fd_flags' in kthread cause kernel crash.  It works fine on
4.1, but causes crash after get 64 fds.  It also cause crash on
ubuntu1404/1604/1804, centos7.5, and the crash messages are almost the
same.

The crash message on centos7.5 shows below:

  start fd 61
  start fd 62
  start fd 63
  BUG: unable to handle kernel NULL pointer dereference at           (null)
  IP: __wake_up_common+0x2e/0x90
  PGD 0
  Oops: 0000 [#1] SMP
  Modules linked in: test(OE) xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ipt_REJECT nf_reject_ipv4 tun bridge stp llc ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter devlink sunrpc kvm_intel kvm irqbypass crc32_pclmul ghash_clmulni_intel aesni_intel lrw gf128mul glue_helper ablk_helper cryptd sg ppdev pcspkr virtio_balloon parport_pc parport i2c_piix4 joydev ip_tables xfs libcrc32c sr_mod cdrom sd_mod crc_t10dif crct10dif_generic ata_generic pata_acpi virtio_scsi virtio_console virtio_net cirrus drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ttm crct10dif_pclmul crct10dif_common crc32c_intel drm ata_piix serio_raw libata virtio_pci virtio_ring i2c_core
   virtio floppy dm_mirror dm_region_hash dm_log dm_mod
  CPU: 2 PID: 1820 Comm: test_fd Kdump: loaded Tainted: G           OE  ------------   3.10.0-862.3.3.el7.x86_64 #1
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.10.2-0-g5f4c7b1-prebuilt.qemu-project.org 04/01/2014
  task: ffff8e92b9431fa0 ti: ffff8e94247a0000 task.ti: ffff8e94247a0000
  RIP: 0010:__wake_up_common+0x2e/0x90
  RSP: 0018:ffff8e94247a2d18  EFLAGS: 00010086
  RAX: 0000000000000000 RBX: ffffffff9d09daa0 RCX: 0000000000000000
  RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffffffff9d09daa0
  RBP: ffff8e94247a2d50 R08: 0000000000000000 R09: ffff8e92b95dfda8
  R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff9d09daa8
  R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000003
  FS:  0000000000000000(0000) GS:ffff8e9434e80000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000000000000 CR3: 000000017c686000 CR4: 00000000000207e0
  Call Trace:
    __wake_up+0x39/0x50
    expand_files+0x131/0x250
    __alloc_fd+0x47/0x170
    get_unused_fd_flags+0x30/0x40
    test_fd+0x12a/0x1c0 [test]
    kthread+0xd1/0xe0
    ret_from_fork_nospec_begin+0x21/0x21
  Code: 66 90 55 48 89 e5 41 57 41 89 f7 41 56 41 89 ce 41 55 41 54 49 89 fc 49 83 c4 08 53 48 83 ec 10 48 8b 47 08 89 55 cc 4c 89 45 d0 <48> 8b 08 49 39 c4 48 8d 78 e8 4c 8d 69 e8 75 08 eb 3b 4c 89 ef
  RIP   __wake_up_common+0x2e/0x90
   RSP <ffff8e94247a2d18>
  CR2: 0000000000000000

This issue exists since CentOS 7.5 3.10.0-862 and CentOS 7.4
(3.10.0-693.21.1 ) is ok.  Root cause: the item 'resize_wait' is not
initialized before being used.

Reported-by: Richard Zhang <zhang.zijian@h3c.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
fs/file: more unsigned file descriptors 2016-09-27T22:47:38+00:00 Alexey Dobriyan adobriyan@gmail.com 2016-09-01T21:38:52+00:00 9b80a184eaadc117f27faad522008f31d571621b Propagate unsignedness for grand total of 149 bytes: $ ./scripts/bloat-o-meter ../vmlinux-000 ../obj/vmlinux add/remove: 0/0 grow/shrink: 0/10 up/down: 0/-149 (-149) function old new delta set_close_on_exec 99 98 -1 put_files_struct 201 200 -1 get_close_on_exec 59 58 -1 do_prlimit 498 497 -1 do_execveat_common.isra 1662 1661 -1 __close_fd 178 173 -5 do_dup2 219 204 -15 seq_show 685 660 -25 __alloc_fd 384 357 -27 dup_fd 718 646 -72 It mostly comes from converting "unsigned int" to "long" for bit operations. Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> 
Propagate unsignedness for grand total of 149 bytes:

	$ ./scripts/bloat-o-meter ../vmlinux-000 ../obj/vmlinux
	add/remove: 0/0 grow/shrink: 0/10 up/down: 0/-149 (-149)
	function                                     old     new   delta
	set_close_on_exec                             99      98      -1
	put_files_struct                             201     200      -1
	get_close_on_exec                             59      58      -1
	do_prlimit                                   498     497      -1
	do_execveat_common.isra                     1662    1661      -1
	__close_fd                                   178     173      -5
	do_dup2                                      219     204     -15
	seq_show                                     685     660     -25
	__alloc_fd                                   384     357     -27
	dup_fd                                       718     646     -72

It mostly comes from converting "unsigned int" to "long" for bit operations.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
give readdir(2)/getdents(2)/etc. uniform exclusion with lseek() 2016-05-02T23:49:28+00:00 Al Viro viro@zeniv.linux.org.uk 2016-04-20T21:08:21+00:00 63b6df14134ddd048984c8afadb46e721815bfc6 same as read() on regular files has, and for the same reason. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> 
same as read() on regular files has, and for the same reason.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
kmemcg: account certain kmem allocations to memcg 2016-01-15T00:00:49+00:00 Vladimir Davydov vdavydov@virtuozzo.com 2016-01-14T23:18:21+00:00 5d097056c9a017a3b720849efb5432f37acabbac Mark those kmem allocations that are known to be easily triggered from userspace as __GFP_ACCOUNT/SLAB_ACCOUNT, which makes them accounted to memcg. For the list, see below: - threadinfo - task_struct - task_delay_info - pid - cred - mm_struct - vm_area_struct and vm_region (nommu) - anon_vma and anon_vma_chain - signal_struct - sighand_struct - fs_struct - files_struct - fdtable and fdtable->full_fds_bits - dentry and external_name - inode for all filesystems. This is the most tedious part, because most filesystems overwrite the alloc_inode method. The list is far from complete, so feel free to add more objects. Nevertheless, it should be close to "account everything" approach and keep most workloads within bounds. Malevolent users will be able to breach the limit, but this was possible even with the former "account everything" approach (simply because it did not account everything in fact). [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Tejun Heo <tj@kernel.org> Cc: Greg Thelen <gthelen@google.com> Cc: Christoph Lameter <cl@linux.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: David Rientjes <rientjes@google.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> 
Mark those kmem allocations that are known to be easily triggered from
userspace as __GFP_ACCOUNT/SLAB_ACCOUNT, which makes them accounted to
memcg.  For the list, see below:

 - threadinfo
 - task_struct
 - task_delay_info
 - pid
 - cred
 - mm_struct
 - vm_area_struct and vm_region (nommu)
 - anon_vma and anon_vma_chain
 - signal_struct
 - sighand_struct
 - fs_struct
 - files_struct
 - fdtable and fdtable->full_fds_bits
 - dentry and external_name
 - inode for all filesystems. This is the most tedious part, because
   most filesystems overwrite the alloc_inode method.

The list is far from complete, so feel free to add more objects.
Nevertheless, it should be close to "account everything" approach and
keep most workloads within bounds.  Malevolent users will be able to
breach the limit, but this was possible even with the former "account
everything" approach (simply because it did not account everything in
fact).

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Greg Thelen <gthelen@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
fs/file.c: __const_max is actually __const_min :-) 2015-12-07T02:17:11+00:00 Rasmus Villemoes linux@rasmusvillemoes.dk 2015-10-29T11:01:41+00:00 752343be63d90c84d275f046e43371febe217863 7f4b36f9bb930 "get rid of files_defer_init()" inexplicably changed a min() to a __const_max() - but the __const_max macro actually gives the minimum... So no functional change, just less confusing naming. Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> 
7f4b36f9bb930 "get rid of files_defer_init()" inexplicably changed a
min() to a __const_max() - but the __const_max macro actually gives
the minimum... So no functional change, just less confusing naming.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
vfs: clear remainder of 'full_fds_bits' in dup_fd() 2015-11-06T07:05:32+00:00 Eric Biggers ebiggers3@gmail.com 2015-11-06T06:32:04+00:00 ea5c58e70c3a148ada0d3061a8f529589bb766ba This fixes a bug from commit f3f86e33dc3d ("vfs: Fix pathological performance case for __alloc_fd()"). v2: refactor to share fd bitmap copying code Signed-off-by: Eric Biggers <ebiggers3@gmail.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> 
This fixes a bug from commit f3f86e33dc3d ("vfs: Fix pathological
performance case for __alloc_fd()").

v2: refactor to share fd bitmap copying code
Signed-off-by: Eric Biggers <ebiggers3@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>