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[Qemu-devel] [PATCH] qemu-char: fix deadlock with "-monitor pty"
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH] qemu-char: fix deadlock with "-monitor pty" |
Date: |
Fri, 11 Jul 2014 12:11:38 +0200 |
qemu_chr_be_generic_open cannot be called with the write lock taken,
because it calls client code that may call qemu_chr_fe_write. This
actually happens for the monitor:
0x00007ffff27dbf79 in __GI_raise (address@hidden)
0x00007ffff27df388 in __GI_abort ()
0x00005555555ef489 in error_exit (err=<optimized out>, address@hidden
<__func__.5959> "qemu_mutex_lock")
0x00005555558f9080 in qemu_mutex_lock (address@hidden)
0x0000555555713936 in qemu_chr_fe_write (s=0x555556248a30, address@hidden
"QEMU 2.0.90 monitor - type 'help' for more information\r\n", len=56)
0x00005555556217fd in monitor_flush_locked (address@hidden)
0x0000555555621a12 in monitor_flush_locked (mon=0x555556251fd0)
monitor_puts (address@hidden, str=0x55555634bfa7 "", address@hidden "QEMU
2.0.90 monitor - type 'help' for more information\n")
0x0000555555624359 in monitor_vprintf (mon=0x555556251fd0, fmt=<optimized
out>, ap=<optimized out>)
0x0000555555624414 in monitor_printf (mon=<optimized out>, address@hidden
"QEMU %s monitor - type 'help' for more information\n")
0x0000555555629806 in monitor_event (opaque=0x555556251fd0,
event=<optimized out>)
0x000055555571343c in qemu_chr_be_generic_open (s=0x555556248a30)
To avoid this, defer the call to an idle callback, which will be
called as soon as the main loop is re-entered. In order to simplify
the cleanup and do it in one place only, change pty_chr_close to
call pty_chr_state.
To reproduce, run with "-monitor pty", then try to read from the
slave /dev/pts/FOO that it creates.
Fixes: 9005b2a7589540a3733b3abdcfbccfe7746cd1a1
Reported-by: Li Liang <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
---
qemu-char.c | 23 +++++++++++++++++++++--
1 file changed, 21 insertions(+), 2 deletions(-)
diff --git a/qemu-char.c b/qemu-char.c
index 51917de..5bf99d1 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -1080,6 +1080,7 @@ typedef struct {
/* Protected by the CharDriverState chr_write_lock. */
int connected;
guint timer_tag;
+ guint open_tag;
} PtyCharDriver;
static void pty_chr_update_read_handler_locked(CharDriverState *chr);
@@ -1092,6 +1093,7 @@ static gboolean pty_chr_timer(gpointer opaque)
qemu_mutex_lock(&chr->chr_write_lock);
s->timer_tag = 0;
+ s->open_tag = 0;
if (!s->connected) {
/* Next poll ... */
pty_chr_update_read_handler_locked(chr);
@@ -1194,12 +1196,26 @@ static gboolean pty_chr_read(GIOChannel *chan,
GIOCondition cond, void *opaque)
return TRUE;
}
+static gboolean qemu_chr_be_generic_open_func(gpointer opaque)
+{
+ CharDriverState *chr = opaque;
+ PtyCharDriver *s = chr->opaque;
+
+ s->open_tag = 0;
+ qemu_chr_be_generic_open(chr);
+ return FALSE;
+}
+
/* Called with chr_write_lock held. */
static void pty_chr_state(CharDriverState *chr, int connected)
{
PtyCharDriver *s = chr->opaque;
if (!connected) {
+ if (s->open_tag) {
+ g_source_remove(s->open_tag);
+ s->open_tag = 0;
+ }
remove_fd_in_watch(chr);
s->connected = 0;
/* (re-)connect poll interval for idle guests: once per second.
@@ -1212,8 +1228,9 @@ static void pty_chr_state(CharDriverState *chr, int
connected)
s->timer_tag = 0;
}
if (!s->connected) {
+ g_assert(s->open_tag == 0);
s->connected = 1;
- qemu_chr_be_generic_open(chr);
+ s->open_tag = g_idle_add(qemu_chr_be_generic_open_func, chr);
}
if (!chr->fd_in_tag) {
chr->fd_in_tag = io_add_watch_poll(s->fd, pty_chr_read_poll,
@@ -1227,7 +1244,8 @@ static void pty_chr_close(struct CharDriverState *chr)
PtyCharDriver *s = chr->opaque;
int fd;
- remove_fd_in_watch(chr);
+ qemu_mutex_lock(&chr->chr_write_lock);
+ pty_chr_state(chr, 0);
fd = g_io_channel_unix_get_fd(s->fd);
g_io_channel_unref(s->fd);
close(fd);
@@ -1235,6 +1253,7 @@ static void pty_chr_close(struct CharDriverState *chr)
g_source_remove(s->timer_tag);
s->timer_tag = 0;
}
+ qemu_mutex_unlock(&chr->chr_write_lock);
g_free(s);
qemu_chr_be_event(chr, CHR_EVENT_CLOSED);
}
--
1.8.3.1
- [Qemu-devel] [PATCH] qemu-char: fix deadlock with "-monitor pty",
Paolo Bonzini <=