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Commit fd30fc32 authored by Tom Zanussi's avatar Tom Zanussi Committed by Linus Torvalds
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[PATCH] relayfs: remove warning printk() in relay_switch_subbuf() 



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.

Signed-off-by: default avatarTom Zanussi <zanussi@us.ibm.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent bb44f116

fs/relayfs/relay.c

+6 −2
Original line number Diff line number Diff line
@@ -333,8 +333,7 @@ size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length) 
	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);

}

include/linux/relayfs_fs.h

+3 −2
Original line number Diff line number Diff line
@@ -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 */

};