• Nikolay Borisov's avatar
    fs/dcache.c: add cond_resched() in shrink_dentry_list() · 32785c05
    Nikolay Borisov authored
    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.comSigned-off-by: default avatarNikolay Borisov <nborisov@suse.com>
    Reviewed-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Acked-by: default avatarDavid 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: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
dcache.c 83.9 KB