The patch titled
Subject: fs/dcache.c: add cond_resched() in shrink_dentry_list()
has been removed from the -mm tree. Its filename was
dcache-add-cond_resched-in-shrink_dentry_list.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Nikolay Borisov <nborisov@xxxxxxxx>
Subject: fs/dcache.c: add cond_resched() in shrink_dentry_list()
As previously reported (https://patchwork.kernel.org/patch/8642031/) it's
possible to call shrink_dentry_list with a large number of dentries (>
10000). This, in turn, could trigger the softlockup detector and possibly
trigger a panic. In addition to the unmount path being vulnerable to this
scenario, at SuSE we've observed similar situation happening during
process exit on processes that touch a lot of dentries. Here is an
excerpt from a crash dump. The number after the colon are the number of
dentries on the list passed to shrink_dentry_list:
PID 99760: 10722
PID 107530: 215
PID 108809: 24134
PID 108877: 21331
PID 141708: 16487
So we want to kill between 15k-25k dentries without yielding.
And one possible call stack looks like:
4 [ffff8839ece41db0] _raw_spin_lock at ffffffff8152a5f8
5 [ffff8839ece41db0] evict at ffffffff811c3026
6 [ffff8839ece41dd0] __dentry_kill at ffffffff811bf258
7 [ffff8839ece41df0] shrink_dentry_list at ffffffff811bf593
8 [ffff8839ece41e18] shrink_dcache_parent at ffffffff811bf830
9 [ffff8839ece41e50] proc_flush_task at ffffffff8120dd61
10 [ffff8839ece41ec0] release_task at ffffffff81059ebd
11 [ffff8839ece41f08] do_exit at ffffffff8105b8ce
12 [ffff8839ece41f78] sys_exit at ffffffff8105bd53
13 [ffff8839ece41f80] system_call_fastpath at ffffffff81532909
While some of the callers of shrink_dentry_list do use cond_resched, this
is not sufficient to prevent softlockups. So just move cond_resched into
shrink_dentry_list from its callers.
David said: I've found hundreds of occurrences of warnings that we emit
when need_resched stays set for a prolonged period of time with the
stack trace that is included in the change log.
Link: http://lkml.kernel.org/r/1521718946-31521-1-git-send-email-nborisov@xxxxxxxx
Signed-off-by: Nikolay Borisov <nborisov@xxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Goldwyn Rodrigues <rgoldwyn@xxxxxxx>
Cc: Jeff Mahoney <jeffm@xxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/dcache.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff -puN fs/dcache.c~dcache-add-cond_resched-in-shrink_dentry_list fs/dcache.c
--- a/fs/dcache.c~dcache-add-cond_resched-in-shrink_dentry_list
+++ a/fs/dcache.c
@@ -1052,6 +1052,8 @@ static void shrink_dentry_list(struct li
while (!list_empty(list)) {
struct dentry *dentry, *parent;
+ cond_resched();
+
dentry = list_entry(list->prev, struct dentry, d_lru);
spin_lock(&dentry->d_lock);
rcu_read_lock();
@@ -1205,7 +1207,6 @@ void shrink_dcache_sb(struct super_block
this_cpu_sub(nr_dentry_unused, freed);
shrink_dentry_list(&dispose);
- cond_resched();
} while (list_lru_count(&sb->s_dentry_lru) > 0);
}
EXPORT_SYMBOL(shrink_dcache_sb);
@@ -1487,7 +1488,6 @@ void shrink_dcache_parent(struct dentry
break;
shrink_dentry_list(&data.dispose);
- cond_resched();
}
}
EXPORT_SYMBOL(shrink_dcache_parent);
@@ -1614,7 +1614,6 @@ void d_invalidate(struct dentry *dentry)
detach_mounts(data.mountpoint);
dput(data.mountpoint);
}
- cond_resched();
}
}
EXPORT_SYMBOL(d_invalidate);
_
Patches currently in -mm which might be from nborisov@xxxxxxxx are
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