Re: 2.6.12-mm1: BUG() in fd_install, RCU related?

[Dipankar Sarma]

On Thu, Jun 23, 2005 at 01:50:11PM +0200, syrius.ml@xxxxxxxxxx wrote:
> Dipankar Sarma <dipankar@xxxxxxxxxx> writes:
> 
> > Some things are common - always with fcntl() or fcntl64() and with
> > a daemon. Does your box come up at all ? If so, can you get me an
> > strace on the process that triggers this ? If I can narrow it
> > down to a small testcase, it would be a lot easier. Also, does
> > switching off CONFIG_PREEMPT fix this problem ?
> 
> I haven't read about this thread. I hope u'll find a way to reproduce
> it. here debian/sid i386 (.config sent in an earlier message), it 100%
> reproducible when restarting bind9. (it also happens on its own on
> different occasion)
> 
> 
> then i restart the daemon:
> 
> end of a strace -f /etc/init.d/bind9 start
> 6541  rt_sigaction(SIGPIPE, {0xb7ca2a70, [], 0}, {SIG_IGN}, 8) = 0
> 6541  send(3, "<30>Jun 23 00:51:35 named[6540]:"..., 82, 0) = 82
> 6541  rt_sigaction(SIGPIPE, {SIG_IGN}, NULL, 8) = 0
> 6541  socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP) = 10
> 6541  fcntl64(10, F_DUPFD, 20)          = 32
> 6541  close(10)                         = 0
> 6541  fcntl64(32, F_GETFL)              = 0x2 (flags O_RDWR)
> 6541  fcntl64(32, F_SETFL, O_RDWR|O_NONBLOCK) = 0
> 6541  setsockopt(32, SOL_SOCKET, SO_TIMESTAMP, [1], 4) = 0
> 6541  setsockopt(32, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
> 6541  bind(32, {sa_family=AF_INET, sin_port=htons(53),
> sin_addr=inet_addr("172.16.254.1")}, 16) = 0
> 6541  socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 10
> 6541  fcntl64(10, F_DUPFD, 20

Aha, this has been extremely helpful. Could you all please try the
following (untested) patch ? This should fix the problem, or
atleast one problem that I can see.

Thanks
Dipankar


locate_fd() may expand fdtable, so the fdtable pointer must be
reloaded after locate_fd().

Signed-of-by: Dipankar Sarma <dipankar@xxxxxxxxxx>
---


 fs/fcntl.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletion(-)

diff -puN fs/fcntl.c~fix-dupfd-reacquire-fdt fs/fcntl.c
--- linux-2.6.12-mm1-fix/fs/fcntl.c~fix-dupfd-reacquire-fdt	2005-06-25 14:56:58.000000000 +0530
+++ linux-2.6.12-mm1-fix-dipankar/fs/fcntl.c	2005-06-25 14:58:26.000000000 +0530
@@ -118,9 +118,10 @@ static int dupfd(struct file *file, unsi
 	int fd;
 
 	spin_lock(&files->file_lock);
-	fdt = files_fdtable(files);
 	fd = locate_fd(files, file, start);
 	if (fd >= 0) {
+		/* locate_fd() may have expanded fdtable, load the ptr */
+		fdt = files_fdtable(files);
 		FD_SET(fd, fdt->open_fds);
 		FD_CLR(fd, fdt->close_on_exec);
 		spin_unlock(&files->file_lock);

_
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