Hi all,
I have a kernel Oops on ppc kernel 2.4.5 with an application listenning
to a high throughput of incoming messages on a netlink socket. The
application is running select() on the netlink socket file descriptor
followed with recvmsg() call (in a forever loop).
The Oops (not saved, and hard to reproduce) showed a crash in the
sock_poll function (kernel/net/socket.c); after investigations, crash is
due to a NULL pointer in f_dentry member of the file structure. This
pointer is set to NULL in the fput (kernel/fs/file_table.c) function.
The backtraces show that the calling function is the sys_recvmsg
(kernel/net/socket.c).
My understanding of the problem is the following:
- When everything goes right:
A/ When netlink socket is opened, its associated file structure is
initialised with f_count to 1, and a dentry;
B/ When select is executed, f_count is increased to 2;
C/ When select ends, f_count is decreased to 1;
D/ When recvmsg is executed, f_count is increased to 2;
E/ When recvmsg ends, f_count is decreased to 1;
F/ Loop forever to B/
- When the problem occurs:
A/ When netlink socket is opened, its associated file structure is
initialised with f_count to 1, and a dentry;
B/ When select is executed, f_count is increased to 2;
C/ When select ends, f_count is decreased to 1;
D/ When recvmsg is executed, f_count is increased to 2;
????/ SOMETHING decreases f_count to 1;
E/ When recvmsg ends, f_count is decreased to 0, AND THEREFORE f_dentry
member of file is set to NULL (since file is considered as not used) ;
F/ When select is executed, f_count is incremented to 1, but f_dentry is
NULL and therefore following code crashes in sock_poll function:
sock = socki_lookup(file->f_dentry->d_inode);
Do you have an idea of the event that could have decreased the f_count
member between D/ and E/ ?
Could you give me elements to continue my investigation ?
Thanks a lot for you help,
Fabien
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This archive was generated by hypermail 2b29 : Wed Jan 23 2002 - 21:00:21 EST