From: Alexey Dobriyan <adobriyan@sw.ru>
To: Roland McGrath <roland@redhat.com>
Cc: akpm@osdl.org, linux-kernel@vger.kernel.org, devel@openvz.org
Subject: Re: utrace, RCU and ia64
Date: Tue, 17 Apr 2007 15:20:48 +0400 [thread overview]
Message-ID: <20070417112048.GA10908@localhost.sw.ru> (raw)
In-Reply-To: <20070329203025.540841801C4@magilla.sf.frob.com>
[double freeing of struct utrace leading to oops in
__rcu_process_callbacks]
Hi, Roland,
utrace debugging you've put into 2.6.21-rc6-mm1 helped. Two double-frees
reproduced:
1) BUG at kernel/utrace.c:176
rcu_utrace_free
utrace_reap
utrace_release_task
release_task
flush_old_exec
load_elf_binary
search_binary_handler
do_execve
2) rcu_utrace_free
check_dead_utrace
remove_detached
finish_report_death
utrace_report_death
do_exit
debug_mutex_init
get_signal_to_deliver
do_notify_resume
ptregscall_common
sysret_signal
----------------
I've sprinkled more atomic_set's over utrace code to determine who is at
fault of first freeing. It seems to be
rcu_utrace_free
check_dead_utrace
wake_quiscent
utrace_detach
It was atomic_set(&utrace->debug, 42) right before wake_quiscent() call
and printk() in rcu_utrace_free() call. So it was 42 or garbage.
How I understand all this is that check_dead_utrace() can free struct
utrace, and don't clear ->utrace pointer.
prev parent reply other threads:[~2007-04-17 11:12 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-03-29 17:07 utrace, RCU and ia64 Alexey Dobriyan
2007-03-29 20:30 ` Roland McGrath
2007-04-17 11:20 ` Alexey Dobriyan [this message]
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