If possible, i.e. if the requested range is resident valid in the vm
object queue, and some secondary conditions hold, copy data for
read(2) directly from the valid cached pages, avoiding vnode lock and
instantiating buffers. I intentionally do not start read-ahead, nor
handle the advises on the cached range.
Filesystems indicate support for VMIO reads by setting VIRF_PGREAD
flag, which must not be cleared until vnode reclamation.
Currently only filesystems that use vnode pager for v_objects can
enable it, due to reliance on vnp_size. There is a WIP to handle it
for tmpfs.
Reviewed by: markj
Discussed with: jeff
Tested by: pho
Benchmarked by: mjg
Sponsored by: The FreeBSD Foundation
Differential revision: https://reviews.freebsd.org/D25968
This removes a lot of special casing from the VFS layer.
Reviewed by: kib (previous version)
Tested by: pho (previous version)
Differential Revision: https://reviews.freebsd.org/D25612
This means there is no expectation lookup will purge the terminal entry,
which simplifies lockless lookup.
Tested by: pho
Sponsored by: The FreeBSD Foundation
- Convert panic() calls to INVARIANTS-only assertions. The PCTRIE code
provides some of the same protection since it will panic upon an
attempt to remove a non-resident buffer.
- Update the comment above reassignbuf() to reflect reality.
Reviewed by: cem, kib, mjg
MFC after: 1 week
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D25965
As the 20-year old comment above it suggests, the counter is of dubious
value. Moreover, the (global) counter was not updated precisely and
hurts scalability.
Reviewed by: cem, kib, mjg
MFC after: 1 week
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D25965
cache_purge locklessly checks whether the vnode at hand has any namecache
entries. This can race with a concurrent purge which managed to remove
the last entry, but may not be done touching the vnode.
Make sure we observe the relevant vnode lock as not taken before proceeding
with vgone.
Paired with the fact that doomed vnodes cannnot receive entries this restores
the invariant that there are no namecache-related writing users past cache_purge
in vgone.
Reported by: pho
Modified on each permission change and link/unlink.
Reviewed by: kib
Tested by: pho (in a patchset)
Differential Revision: https://reviews.freebsd.org/D25573
Convert the bufobj tries to an SMR zone/PCTRIE and add a gbincore_unlocked()
API wrapping this functionality. Use it for a fast path in getblkx(),
falling back to locked lookup if we raced a thread changing the buf's
identity.
Reported by: Attilio
Reviewed by: kib, markj
Testing: pho (in progress)
Sponsored by: Isilon
Differential Revision: https://reviews.freebsd.org/D25782
vget_prep_smr and vhold_smr can be used to ref a vnode while within vfs_smr
section, allowing consumers to get away without locking.
See vhold_smr and vdropl for comments explaining caveats.
Reviewed by: kib
Testec by: pho
Differential Revision: https://reviews.freebsd.org/D23913
Comparing fsid_t objects requires internal knowledge of the fsid structure
and yet this is duplicated across a number of places in the code.
Simplify by creating a fsidcmp function (macro).
Reviewed by: mjg, rmacklem
Approved by: mav (mentor)
MFC after: 1 week
Sponsored by: iXsystems, Inc.
Differential Revision: https://reviews.freebsd.org/D24749
file systems to safely access their disk devices, and adapt FFS to use it.
Also add a new BO_NOBUFS flag to allow enforcing that file systems using
mntfs vnodes do not accidentally use the original devfs vnode to create buffers.
Reviewed by: kib, mckusick
Approved by: imp (mentor)
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D23787
virtual address or physical page allocation need to be marked with this
flag.
Reviewed by: markj
Tested by: pho
Differential Revision: https://reviews.freebsd.org/D23712
The routine was checking for ->v_type == VBAD. Since vgone drops the interlock
early sets this type at the end of the process of dooming a vnode, this opens
a time window where it can clear the pointer while the inerlock-holders is
accessing it.
Another note is that the code was:
(vp->v_object != NULL &&
vp->v_object->resident_page_count > trigger)
With the compiler being fully allowed to emit another read to get the pointer,
and in fact it did on the kernel used by pho.
Use atomic_load_ptr and remember the result.
Note that this depends on type-safety of vm_object.
Reported by: pho
In particular on amd64 this eliminates an atomic op in the common case,
trading it for IPIs in the uncommon case of catching CPUs executing the
code while the filesystem is getting suspended or unmounted.
vdrop can set the hold count to 0 and wait for the ->mnt_listmtx held by
mnt_vnode_next_lazy_relock caller. The routine incorrectly asserted the
count has to be > 0.
Reported by: pho
Tested by: pho
The race is:
CPU1 CPU2
devfs_reclaim_vchr
make v_usecount 0
VI_LOCK
sees v_usecount == 0, no updates
vp->v_rdev = NULL;
...
VI_UNLOCK
VI_LOCK
v_decr_devcount
sees v_rdev == NULL, no updates
In this scenario si_devcount decrement is not performed.
Note this can only happen if the vnode lock is not held.
Reviewed by: kib
Tested by: pho
Differential Revision: https://reviews.freebsd.org/D23529
vrele is supposed to be called with an unlocked vnode, but this was never
asserted for if v_usecount was > 0. For such counts the lock is never touched
by the routine. As a result the kernel has several consumers which expect
vunref semantics and get away with calling vrele since they happen to never do
it when this is the last reference (and for some of them this may happen to be
a guarantee).
Work around the problem by changing vrele semantics to tolerate being called
with a lock. This eliminates a possible bug where the lock is already held and
vputx takes it anyway.
Reviewed by: kib
Tested by: pho
Differential Revision: https://reviews.freebsd.org/D23528
O_SEARCH is defined by POSIX [0] to open a directory for searching, skipping
permissions checks on the directory itself after the initial open(). This is
close to the semantics we've historically applied for O_EXEC on a directory,
which is UB according to POSIX. Conveniently, O_SEARCH on a file is also
explicitly undefined behavior according to POSIX, so O_EXEC would be a fine
choice. The spec goes on to state that O_SEARCH and O_EXEC need not be
distinct values, but they're not defined to be the same value.
This was pointed out as an incompatibility with other systems that had made
its way into libarchive, which had assumed that O_EXEC was an alias for
O_SEARCH.
This defines compatibility O_SEARCH/FSEARCH (equivalent to O_EXEC and FEXEC
respectively) and expands our UB for O_EXEC on a directory. O_EXEC on a
directory is checked in vn_open_vnode already, so for completeness we add a
NOEXECCHECK when O_SEARCH has been specified on the top-level fd and do not
re-check that when descending in namei.
[0] https://pubs.opengroup.org/onlinepubs/9699919799/
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D23247
