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restorer: fix a race condition between access and unmap to task_entries

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If we have tree threads, a following situation can occur:

T2: dec task_entries->nr_in_progress
T3: dec task_entries->nr_in_progress
T3: futex(&task_entries->nr_in_progress, WAKE_UP);
T1: unmap task_entries
T2: futex(&task_entries->nr_in_progress, WAKE_UP) -> EFAULT -> BUG_ON()

This patch adds a futex for synchronising threads.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
This commit is contained in:
Andrey Vagin 2012-11-26 18:46:11 +04:00 committed by Pavel Emelyanov
parent 6b1d64ca9a
commit bae333dfcb
1 changed files with 8 additions and 0 deletions
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8
pie/restorer.c
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@ -36,6 +36,7 @@
})
static struct task_entries *task_entries;
static futex_t thread_inprogress;
static void sigchld_handler(int signal, siginfo_t *siginfo, void *data)
{
@ -237,6 +238,8 @@ long __export_restore_thread(struct thread_restore_args *args)
futex_wait_while(&task_entries->start, CR_STATE_RESTORE);
futex_dec_and_wake(&task_entries->nr_in_progress);
futex_wait_while(&task_entries->start, CR_STATE_RESTORE_SIGCHLD);
futex_dec_and_wake(&thread_inprogress);
new_sp = (long)rt_sigframe + 8;
asm volatile(
@ -737,10 +740,15 @@ long __export_restore_task(struct task_restore_core_args *args)
sys_sigaction(SIGCHLD, &args->sigchld_act, NULL, sizeof(rt_sigset_t));
futex_set_and_wake(&thread_inprogress, args->nr_threads);
futex_dec_and_wake(&args->task_entries->nr_in_progress);
futex_wait_while(&args->task_entries->start, CR_STATE_RESTORE_SIGCHLD);
/* Wait until children stop to use args->task_entries */
futex_wait_while_gt(&thread_inprogress, 1);
rst_tcp_socks_all(args->rst_tcp_socks, args->rst_tcp_socks_size);
log_set_fd(-1);