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Subject[RFC, PATCH] cond_resched() added to close_files()
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When a process exits, it might spend a lot of time in close_files() closing 
thousand of files.

This is bad for latency, and in some cases can trigger 'BUG: soft lockup
detected on CPU#0!'

Call Trace: <IRQ> <ffffffff8024dafa>{softlockup_tick+250}
<ffffffff80236cd7>{update_process_times+87}
<ffffffff80215ed3>{smp_local_timer_interrupt+35}
<ffffffff80216411>{smp_apic_timer_interrupt+65}
<ffffffff8020a866>{apic_timer_interrupt+98} <EOI>
<ffffffff803a7100>{sock_destroy_inode+0}
<ffffffff803e4b1f>{tcp_send_fin+207}
<ffffffff803e4ac4>{tcp_send_fin+116} <ffffffff803d988a>{tcp_close+698}
<ffffffff803f4a07>{inet_release+87} <ffffffff803a84e9>{sock_release+25}
<ffffffff803a87f5>{sock_close+53} <ffffffff802767a8>{__fput+88}
<ffffffff8027382d>{filp_close+93}
<ffffffff8022ee2e>{put_files_struct+110}
<ffffffff8023025a>{do_exit+650}
<ffffffff80237bee>{__dequeue_signal+478}
<ffffffff80230998>{do_group_exit+200}
<ffffffff80239c6a>{get_signal_to_deliver+1178}
<ffffffff80209d47>{sysret_signal+28} <ffffffff80209001>{do_signal+129}
<ffffffff8028d623>{dput+35} <ffffffff803a92db>{sys_accept+443}
<ffffffff80241eec>{add_wait_queue+28} <ffffffff802ec581>{__up_write+33}
<ffffffff80209d47>{sysret_signal+28}
<ffffffff8020a033>{ptregscall_common+103}
This patch makes sure a cond_resched() call is done every 32 (or 64) files
closed. This also helps reducing number of files waiting in RCU queues for
final freeing as call_rcu() might have called force_quiescent_state()

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
--- a/kernel/exit.c 2006-05-02 17:31:39.000000000 +0200
+++ b/kernel/exit.c 2006-05-02 17:32:06.000000000 +0200
@@ -445,20 +445,21 @@
set = fdt->open_fds->fds_bits[j++];
while (set) {
if (set & 1) {
struct file * file = xchg(&fdt->fd[i], NULL);
if (file)
filp_close(file, files);
}
i++;
set >>= 1;
}
+ cond_resched();
}
}

struct files_struct *get_files_struct(struct task_struct *task)
{
struct files_struct *files;

task_lock(task);
files = task->files;
if (files)
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