Date: Sat, 16 May 2026 11:47:12 +0200 From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@FreeBSD.org> To: current@freebsd.org Cc: kib@freebsd.org Subject: rms_rlock with non-sleepable locks held Message-ID: <86lddjelen.fsf@ltc.des.dev>
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On recent main with a debugging kernel, I am unable to build anything as
the system slows to a crawl while the console is inundated with stack
traces:
rms_rlock with the following non-sleepable locks held:
exclusive sleep mutex kqueue (kqueue) r = 0 (0xfffff8013615cc00) locked @ /usr/src/sys/kern/kern_event.c:2588
stack backtrace:
#0 0xffffffff805d571c at witness_debugger+0x6c
#1 0xffffffff805d7019 at witness_warn+0x4b9
#2 0xffffffff8055841f at rms_rlock+0x1f
#3 0xffffffff81418f08 at zfs_freebsd_getattr+0xb8
#4 0xffffffff808c1ede at VOP_GETATTR_APV+0x4e
#5 0xffffffff8065add0 at vn_getsize_locked+0x70
#6 0xffffffff806610c2 at filt_vfsread+0x82
#7 0xffffffff805018f4 at knote+0xc4
#8 0xffffffff80658f2e at vop_open_post+0x3e
#9 0xffffffff808c1572 at VOP_OPEN_APV+0x92
#10 0xffffffff8066e67b at vn_open_vnode+0x19b
#11 0xffffffff8066de18 at vn_open_cred+0x698
#12 0xffffffff8066364e at openatfp+0x2be
#13 0xffffffff8066336d at sys_openat+0x3d
#14 0xffffffff822153a2 at filemon_wrapper_openat+0x12
#15 0xffffffff808a05b8 at amd64_syscall+0x168
#16 0xffffffff8086f86b at fast_syscall_common+0xf8
They vary in how they get to knote() but they're all the same from frame
7 and up.
BTW, filt_vfsread() is an excellent argument for VOP_GETSIZE, with
vn_getsize() falling back to a full VOP_GETATTR() only when the vnode's
vop table does not provide it, as the size of a ZFS vnode is very easy
to get:
size_t zfs_getsize(vnode_t *vp) { return (VTOZ(vp)->z_size); }
while a full VOP_GETATTR() is several hundred lines of code.
DES
--
Dag-Erling Smørgrav - des@FreeBSD.org
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