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author | Nikolay Borisov <nborisov@suse.com> | 2018-04-11 01:35:49 +0200 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2018-04-11 19:28:38 +0200 |
commit | 32785c0539b7e96f77a14a4f4ab225712665a5a4 (patch) | |
tree | aa35ab493a0b2f84e4ed19b3a8b46c69b6aa2573 /fs/dcache.c | |
parent | include/linux/kfifo.h: fix comment (diff) | |
download | linux-32785c0539b7e96f77a14a4f4ab225712665a5a4.tar.xz linux-32785c0539b7e96f77a14a4f4ab225712665a5a4.zip |
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@suse.com
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Goldwyn Rodrigues <rgoldwyn@suse.de>
Cc: Jeff Mahoney <jeffm@suse.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/dcache.c')
-rw-r--r-- | fs/dcache.c | 5 |
1 files changed, 2 insertions, 3 deletions
diff --git a/fs/dcache.c b/fs/dcache.c index 915816e90049..86d2de63461e 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1052,6 +1052,8 @@ static void shrink_dentry_list(struct list_head *list) 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 *sb) 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 *parent) 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); |