2005-12-20 18:35:46

by Tom Zanussi

[permalink] [raw]
Subject: [PATCH] relayfs: remove warning printk() in relay_switch_subbuf()

Hi,

There's currently a diagnostic printk in relay_switch_subbuf() meant
as a warning if you accidentally try to log an event larger than the
sub-buffer size. The problem is if this happens while logging from
somewhere it's not safe to be doing printks, such as in the scheduler,
you can end up with a deadlock. This patch removes the warning from
relay_switch_subbuf() and instead prints some diagnostic info when the
channel is closed.

Thanks to Mathieu Desnoyers for pointing out the problem and
suggesting a fix.

Tom

Signed-off-by: Tom Zanussi <[email protected]>

diff --git a/fs/relayfs/relay.c b/fs/relayfs/relay.c
--- a/fs/relayfs/relay.c
+++ b/fs/relayfs/relay.c
@@ -333,8 +333,7 @@ size_t relay_switch_subbuf(struct rchan_
return length;

toobig:
- printk(KERN_WARNING "relayfs: event too large (%Zd)\n", length);
- WARN_ON(1);
+ buf->chan->last_toobig = length;
return 0;
}

@@ -399,6 +398,11 @@ void relay_close(struct rchan *chan)
relay_close_buf(chan->buf[i]);
}

+ if (chan->last_toobig)
+ printk(KERN_WARNING "relayfs: one or more items not logged "
+ "[item size (%Zd) > sub-buffer size (%Zd)]\n",
+ chan->last_toobig, chan->subbuf_size);
+
kref_put(&chan->kref, relay_destroy_channel);
}

diff --git a/include/linux/relayfs_fs.h b/include/linux/relayfs_fs.h
--- a/include/linux/relayfs_fs.h
+++ b/include/linux/relayfs_fs.h
@@ -20,9 +20,9 @@
#include <linux/kref.h>

/*
- * Tracks changes to rchan_buf struct
+ * Tracks changes to rchan/rchan_buf structs
*/
-#define RELAYFS_CHANNEL_VERSION 5
+#define RELAYFS_CHANNEL_VERSION 6

/*
* Per-cpu relay channel buffer
@@ -60,6 +60,7 @@ struct rchan
struct rchan_callbacks *cb; /* client callbacks */
struct kref kref; /* channel refcount */
void *private_data; /* for user-defined data */
+ size_t last_toobig; /* tried to log event > subbuf size */
struct rchan_buf *buf[NR_CPUS]; /* per-cpu channel buffers */
};