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); _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
