Date: Wed, 14 Jan 2009 08:32:13 +0100 From: Christoph Mallon <christoph.mallon@gmx.de> To: FreeBSD Current <freebsd-current@freebsd.org> Cc: uwe@grohnwaldt.eu, miwi@freebsd.org Subject: Question about panic in brelse() Message-ID: <496D94FD.9030300@gmx.de>
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Hi,
I wrote this to hackers@ two days ago, but I got no response so far.
Maybe somebody with some VFS experience sees it on this list.
I observe a failed assertion in the VFS regarding a buffer. I
investigated a bit and now I want to present my findings and I have a
question:
Assume I have a buffer with
b_iocmd = BIO_WRITE
b_ioflags = BIO_ERROR
b_error = EIO
b_flags = B_NOCACHE
passed to brelse() in kern/vfs_bio.c[0].
- This particular combination of values (line 1144) causes BIO_ERROR to
be cleared (line 1152) and B_DELWRI is set in bdirty() (line 1031,
called in line 1153).
- Because of B_NOCACHE (line 1343) this buffer gets moved to QUEUE_CLEAN
(line 1349). Also B_INVAL gets set here (line 1345).
- A few lines down (line 1375) bundirty() gets called because of B_INVAL
and B_DELWRI.
- bundirty() instantly panics because the buffer is not in QUEUE_NONE
(line 1075).
My question is: Is this a bug in brelse() or was the combination of flag
B_NOCACHE with a failed write attempt (BIO_WRITE, BIO_ERROR, EIO)
invalid when the buffer was passed to brelse()?
Below is a dump of the buffer right when the assertion is triggered. If
you want any further information about this issue, please tell me.
Hopefully somebody can shed some light on this
Christoph
{
b_bufobj = 0xffffff0030005e00,
b_bcount = 16384,
b_caller1 = 0x0,
b_data = 0xfffffffea2c57000 "",
b_error = 5, (EIO)
b_iocmd = 2 '\002', (BIO_WRITE)
b_ioflags = 2 '\002', (BIO_DONE)
b_iooffset = 98304,
b_resid = 16384,
b_iodone = 0,
b_blkno = 192,
b_offset = 98304,
b_bobufs = { tqe_next = 0x0, tqe_prev = 0xffffff0030005e40},
b_left = 0x0,
b_right = 0x0,
b_vflags = 0,
b_freelist = {
tqe_next = 0xfffffffe92d747c8,
tqe_prev = 0xffffffff80d340f0
},
b_qindex = 1, (QUEUE_CLEAN)
b_flags = 41092, (B_NOCACHE | b_INVAL | B_DELWRI | B_ASYNC)
b_xflags = 33 '!',
b_lock = {
lock_object = {
lo_name = 0xffffffff808d01b6 "bufwait",
lo_flags = 91947008,
lo_data = 0,
lo_witness = 0xfffffffe40206180
},
lk_lock = 18446744073709551608,
lk_timo = 0,
lk_pri = 80
},
b_bufsize = 16384,
b_runningbufspace = 0,
b_kvabase = 0xfffffffea2c57000 "",
b_kvasize = 16384,
b_lblkno = 192,
b_vp = 0xffffff0030005ce8,
b_dirtyoff = 0,
b_dirtyend = 0,
b_rcred = 0x0,
b_wcred = 0x0,
b_saveaddr = 0xfffffffea2c57000,
b_pager = {pg_reqpage = 0},
b_cluster = {
cluster_head = {
tqh_first = 0xfffffffe92d747c8,
tqh_last = 0xfffffffe92d73ad0
},
cluster_entry = {
tqe_next = 0xfffffffe92d747c8,
tqe_prev = 0xfffffffe92d73ad0
}
},
b_pages = {
0xffffff00de3ce5a0, 0xffffff00de3ce610,
0xffffff00de3ce680, 0xffffff00de3ce6f0,
$0x0 <repeats 28 times>
},
b_npages = 4,
b_dep = { lh_first = 0x0 },
b_fsprivate1 = 0x0,
b_fsprivate2 = 0x0,
b_fsprivate3 = 0x0,
b_pin_count = 0
}
[0] r183754 in head/, which is the latest version of kern/vfs_bio.c.
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