Dominique Martinet wrote on Thu, Jul 30, 2015 at 01:50:45PM +0200:
> > My guess is that I'm just seeing a race condition that already existed
> > but the barriers make it easier to reproduce it.
> > This commit came with 2b0143b5c9 "VFS: normal filesystems (and lustre):
> > d_inode() annotations" which made 9P access d_inode through the helper,
> > which could have helped with ordering, but I'm still hitting the bug
> > "easily" with that commit.
>
> Still looking for ideas to help diagnose further...
Slowly progressing, through carefully placed systemtap probes I got down
to this check in link_path_walk in fs/namei.c:
if (!d_can_lookup(nd->path.dentry)) {
err = -ENOTDIR;
break;
}
going all the way to path_init -> path_openat -> do_filp_open -> user.
Could then add a break in gdb on the err = -ENOTDIR instruction:
#0 link_path_walk (name=0xffff88042b47b027 "f", nd=0xffff88042c19eff8)
at fs/namei.c:1845
#1 0xffffffff81209209 in path_init (dfd=<optimized out>, name=<optimized out>,
flags=64, nd=0x1 <irq_stack_union+1>) at fs/namei.c:1952
#2 0xffffffff8120bd42 in path_openat (dfd=<optimized out>, pathname=0xffff88042b47b000,
nd=0xffff88042a9cfe28, op=0xffff88042a9cff1c, flags=65) at fs/namei.c:3230
#3 0xffffffff8120d8e9 in do_filp_open (dfd=-100, pathname=0xffff88042b47b000,
op=0xffff88042a9cff1c) at fs/namei.c:3280
#4 0xffffffff811fb2d7 in do_sys_open (dfd=683933728, filename=<optimized out>,
flags=<optimized out>, mode=<optimized out>) at fs/open.c:1010
#5 0xffffffff811fb3fe in SYSC_open (mode=<optimized out>, flags=<optimized out>,
filename=<optimized out>) at fs/open.c:1028
#6 SyS_open (filename=<optimized out>, flags=<optimized out>, mode=<optimized out>)
at fs/open.c:1023
Unfortunately can't seem to get much more out of it, nd->path is borked
by the time gdb gets here:
(gdb) p nd->path
$1 = {mnt = 0x6f666e69000064, dentry = 0x7379656b64616564}
Looking at other values around:
- next->dentry seems to be the last dir (need to rename directories in
my test to check, bad idea to name them all the same)
- name is the name of the file that does exist
It's easy enough to reproduce for me with the script I got, so happy to
give more infos if someone has an idea...
--
Dominique
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