NULL pointer dereference in print_daily_error_info

[Sergey Senozhatsky]

Hello,
      
This patch fixes NULL pointer dereference in print_daily_error_info, when   
called
on unmounted fs (EXT4_SB(sb) returns NULL). Deleting error reporting timer  
in
ext4_put_super fixes oops.

IRQ:
run_timer_softirq
?run_timer_softirq
print_daily_error_info
?__do_softirq
__do_softirq
call_softirq
do_softirq
irq_exit
smp_apic_timer_interrupt
apic_timer_interrupt
EOI
intel_idle
intel_idle
...


By the way, isn't print_daily_error_info racy? Is it safe to call           
print_daily_error_info
(by timer event (softirq)) when we'are remounting fs, etc.?

Please kindly review.

---

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 2614774..751997d 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -719,6 +719,7 @@ static void ext4_put_super(struct super_block *sb)
 			ext4_abort(sb, "Couldn't clean up the journal");
 	}
 
+	del_timer(&sbi->s_err_report);
 	ext4_release_system_zone(sb);
 	ext4_mb_release(sb);
 	ext4_ext_release(sb);

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