All vnodes allocated by UMA are present on the global list used by
vnlru. getnewvnode modifies the state of the vnode (most notably
altering v_holdcnt) but never locks it. Moreover filesystems also
modify it in arbitrary manners sometimes before taking the vnode
lock or adding any other indicator that the vnode can be used.
Picking up such a vnode by vnlru would be problematic.
To that end there are 2 fixes:
- vlrureclaim, not recycling v_holdcnt == 0 vnodes, takes the
interlock and verifies that v_mount has been set. It is an
invariant that the vnode lock is held by that point, providing
the necessary serialisation against locking after vhold.
- vnlru_free_locked, only wanting to free v_holdcnt == 0 vnodes,
now makes sure to only transition the count 0->1 and newly allocated
vnodes start with v_holdcnt == VHOLD_NO_SMR. getnewvnode will only
transition VHOLD_NO_SMR->1 once more making the hold fail
Tested by: pho
It no longer protects any of tested fields, keeping all the checks racy.
While here make vtryrecycle drop the vnode on its own. Avoids an additional
lock trip.
mkdir -p /foo/bar/baz will mkdir each path component and ignore EEXIST.
The NOCACHE lookup will make the namecache unnecessarily evict the existing entry,
and then fallback to the fs lookup routine eventually leading namei to return an
error as the directory is already there.
For invocations like mkdir -p /usr/obj/usr/src/sys/GENERIC/modules this triggers
fallbacks to the slowpath for concurrently executing lookups.
Tested by: pho
Discussed with: kib
It is a common pattern for filesystems' VOP_INACTIVE() implementation
to forcibly reclaim the vnode when its state is final. For instance,
UFS vnode with zero link count is removed, and since it is
inactivated, the last open reference on it is dropped.
On the other hand, vnode might get spurious usecount reference for
many reasons. If the spurious reference exists while vgonel() checks
for active state of the vnode, it would recurse into VOP_INACTIVE().
Fix it by checking and not doing inactivation when vgone() was called
from inactive VOP.
Reported and tested by: pho
Discussed with: mjg
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
There are several negative side-effects of not calling into VOP layer
at all for page cache reads. The biggest is the missed activation of
EVFILT_READ knotes.
Also, it allows filesystem to make more fine grained decision to
refuse read from page cache.
Keep VIRF_PGREAD flag around, it is still useful for nullfs, and for
asserts.
Reviewed by: markj
Tested by: pho
Discussed with: mjg
Sponsored by: The FreeBSD Foundation
Differential revision: https://reviews.freebsd.org/D26346
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
