[RCU problem] was VFS: file-max limit 50044 reached

[Eric Dumazet <dada1@cosmosbay.com>]

Dipankar Sarma a écrit :
> On Mon, Oct 17, 2005 at 11:10:04AM +0200, Eric Dumazet wrote:
> > Fixing the 'file count' wont fix the real problem : Batch freeing is good 
> > but should be limited so that not more than *billions* of file struct are 
> > queued for deletion.
>
>
> Agreed. It is not designed to work that way, so there must be
> a bug somewhere and I am trying to track it down. It could very well
> be that at maxbatch=10 we are just queueing at a rate far too high
> compared to processing.

I can freeze my test machine with a program that 'only' use dentries, no files.

No message, no panic, but machine becomes totally unresponsive after few seconds.

Just greping for call_rcu in kernel sources gave me another call_rcu() use 
from syscalls. And yes 2.6.13 has the same problem.

Here is the killer on by HT Xeon machine (2GB ram)

Eric

#include <unistd.h>
#include <sys/types.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/stat.h>

int main(void)
{
	int i, rc;	
	struct stat st;
	char name[1024];

	memset(name, 'a', sizeof(name));

	for (i = 0; i < 1000000000;i++) {
		sprintf(name + 220, "%d", i);
		rc = stat(name, &st);
		if (rc == -1 && errno != ENOENT) {
			perror(name);
		}
	}
	return 0;
}