Running the following command:

 busybox cat /sys/kernel/debug/tracing/trace_pipe > /dev/null

with any tracing enabled pretty very quickly leads to various NULL
pointer dereferences and VM BUG_ON()s, such as these:

 BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
 IP: [<ffffffff8119df6c>] generic_pipe_buf_release+0xc/0x40
 Call Trace:
  [<ffffffff811c48a3>] splice_direct_to_actor+0x143/0x1e0
  [<ffffffff811c42e0>] ? generic_pipe_buf_nosteal+0x10/0x10
  [<ffffffff811c49cf>] do_splice_direct+0x8f/0xb0
  [<ffffffff81196869>] do_sendfile+0x199/0x380
  [<ffffffff81197600>] SyS_sendfile64+0x90/0xa0
  [<ffffffff8192cbee>] entry_SYSCALL_64_fastpath+0x12/0x6d

 page dumped because: VM_BUG_ON_PAGE(atomic_read(&page->_count) == 0)
 kernel BUG at include/linux/mm.h:367!
 invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
 RIP: [<ffffffff8119df9c>] generic_pipe_buf_release+0x3c/0x40
 Call Trace:
  [<ffffffff811c48a3>] splice_direct_to_actor+0x143/0x1e0
  [<ffffffff811c42e0>] ? generic_pipe_buf_nosteal+0x10/0x10
  [<ffffffff811c49cf>] do_splice_direct+0x8f/0xb0
  [<ffffffff81196869>] do_sendfile+0x199/0x380
  [<ffffffff81197600>] SyS_sendfile64+0x90/0xa0
  [<ffffffff8192cd1e>] tracesys_phase2+0x84/0x89

(busybox's cat uses sendfile(2), unlike the coreutils version)

This is because tracing_splice_read_pipe() can call splice_to_pipe()
with spd->nr_pages == 0.  spd_pages underflows in splice_to_pipe() and
we fill the page pointers and the other fields of the pipe_buffers with
garbage.

All other callers of splice_to_pipe() avoid calling it when nr_pages ==
0, and we could make tracing_splice_read_pipe() do that too, but it
seems reasonable to have splice_to_page() handle this condition
gracefully.

Cc: stable@vger.kernel.org
Signed-off-by: Rabin Vincent <rabin@rab.in>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Explicitly check show_devname method return code and bail out in case
of an error.  This fixes regression introduced by commit 9d4d6574.

Cc: stable@vger.kernel.org
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

d_add() with inode->i_lock already held; common to d_add() and
d_splice_alias().  All ->lookup() instances that end up hashing
the dentry they are given will hash it here.

This almost completes the preparations to parallel lookups
proper - the only remaining bit is taking security_d_instantiate()
past d_rehash() and doing rehashing without dropping ->d_lock.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

it's a no-op - bumping ->d_seq is pointless there.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

First of all, don't bother calling it if inode is NULL -
that makes inode argument unused.  Moreover, do it *before*
dropping ->d_lock, not right after that (and don't bother
grabbing ->d_lock in it, of course).
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

new primitive: d_exact_alias(dentry, inode).  If there is an unhashed
dentry with the same name/parent and given inode, rehash, grab and
return it.  Otherwise, return NULL.  The only caller of d_add_unique()
switched to d_exact_alias() + d_splice_alias().
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

the last user is gone
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

... and use d_add(dn, NULL) in case we need to hash a negative
unhashed rather than using d_rehash() directly.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

... and turn it into d_add in there
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

d_splice_alias() guarantees that it'll be always hashed
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

... and make mountpoint_last() use it.  That makes all
candidates for lookup with parent locked shared go
through lookup_slow().
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Return dentry and don't pass nameidata or path; lift crossing mountpoints
into the caller.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

No need to lock parent just because of ->d_revalidate() on child;
contrary to the stale comment, lookup_dcache() *can* be used without
locking the parent.  Result can be moved as soon as we return, of
course, but the same is true for lookup_one_len_unlocked() itself.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Have lookup_fast() return 1 on success and 0 on "need to fall back";
lookup_slow() and follow_managed() return positive (1) on success.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

d_instantiate(new_dentry, old_inode) is absolutely wrong thing to
do - it will oops if new_dentry used to be positive, for starters.
What we need is d_invalidate() the target and be done with that.

Cc: stable@vger.kernel.org # v3.18+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Failing to allocate an inode for child means that cache for *parent* is
incompletely populated.  So it's parent directory inode ('dir') that
needs NCPI_DIR_CACHE flag removed, *not* the child inode ('inode', which
is what we'd failed to allocate in the first place).

Fucked-up-in: commit 5e993e25 ("ncpfs: get rid of d_validate() nonsense")
Fucked-up-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@vger.kernel.org # v3.19
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

... and kill need_lookup thing
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

bugger off on negatives a bit earlier, simplify the tests
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

for the sake of namei.c fixes

Now that applications need to explicitly ask for polling we can enable it
by default in blk-mq drivers.  Note that this will only have an affect
on driver that supply a poll function, which currently only includes nvme.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Stephen Bates <stephen.bates@pmcs.com>
Tested-by: Stephen Bates <stephen.bates@pmcs.com>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Stephen Bates <stephen.bates@pmcs.com>
Tested-by: Stephen Bates <stephen.bates@pmcs.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

This adds a flag that tells the file system that this is a high priority
request for which it's worth to poll the hardware.  The flag is purely
advisory and can be ignored if not supported.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Stephen Bates <stephen.bates@pmcs.com>
Tested-by: Stephen Bates <stephen.bates@pmcs.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Signed-off-by: Milosz Tanski <milosz@adfin.com>
[hch: rebased due to newly added syscalls]
Reviewed-by: Stephen Bates <stephen.bates@pmcs.com>
Tested-by: Stephen Bates <stephen.bates@pmcs.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

New syscalls that take an flag argument.   No flags are added yet in this
patch.
Signed-off-by: Milosz Tanski <milosz@adfin.com>
[hch: rebased on top of my kiocb changes]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Stephen Bates <stephen.bates@pmcs.com>
Tested-by: Stephen Bates <stephen.bates@pmcs.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

This way we can set kiocb flags also from the sync read/write path for
the read_iter/write_iter operations.  For now there is no way to pass
flags to plain read/write operations as there is no real need for that,
and all flags passed are explicitly rejected for these files.
Signed-off-by: Milosz Tanski <milosz@adfin.com>
[hch: rebased on top of my kiocb changes]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Stephen Bates <stephen.bates@pmcs.com>
Tested-by: Stephen Bates <stephen.bates@pmcs.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Games with ordering and barriers are way too brittle.  Just
bump ->d_seq before and after updating ->d_inode and ->d_flags
type bits, so that verifying ->d_seq would guarantee they are
coherent.

Cc: stable@vger.kernel.org # v3.13+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

... or we risk seeing a bogus value of d_is_symlink() there.

Cc: stable@vger.kernel.org # v4.2+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

... otherwise d_is_symlink() above might have nothing to do with
the inode value we've got.

Cc: stable@vger.kernel.org # v4.2+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

both do_last() and walk_component() risk picking a NULL inode out
of dentry about to become positive, *then* checking its flags and
seeing that it's not negative anymore and using (already stale by
then) value they'd fetched earlier.  Usually ends up oopsing soon
after that...

Cc: stable@vger.kernel.org # v3.13+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

... into returning a positive to path_openat(), which would interpret that
as "symlink had been encountered" and proceed to corrupt memory, etc.
It can only happen due to a bug in some ->open() instance or in some LSM
hook, etc., so we report any such event *and* make sure it doesn't trick
us into further unpleasantness.

Cc: stable@vger.kernel.org # v3.6+, at least
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

-EBADF is a rather confusing error if an operations is not supported,
and nfsd gets rather upset about it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

The delete opration can allocate additional space on the HPFS filesystem
due to btree split. The HPFS driver checks in advance if there is
available space, so that it won't corrupt the btree if we run out of space
during splitting.

If there is not enough available space, the HPFS driver attempted to
truncate the file, but this results in a deadlock since the commit
7dd29d8d ("HPFS: Introduce a global mutex
and lock it on every callback from VFS").

This patch removes the code that tries to truncate the file and -ENOSPC is
returned instead. If the user hits -ENOSPC on delete, he should try to
delete other files (that are stored in a leaf btree node), so that the
delete operation will make some space for deleting the file stored in
non-leaf btree node.
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Mikulas Patocka <mikulas@artax.karlin.mff.cuni.cz>
Cc: stable@vger.kernel.org	# 2.6.39+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>