linux-kernel - Re: [PATCH v8] sbitmap: fix io hung due to race on sbitmap

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-Id: <172140359332.12097.1558892281494577679.b4-ty@kernel.dk>
Date: Fri, 19 Jul 2024 09:39:53 -0600
From: Jens Axboe <axboe@...nel.dk>
To: Bart Van Assche <bvanassche@....org>, 
 Andrew Morton <akpm@...ux-foundation.org>, Ming Lei <ming.lei@...hat.com>, 
 Omar Sandoval <osandov@...com>, linux-kernel@...r.kernel.org, 
 linux-block@...r.kernel.org, Yang Yang <yang.yang@...o.com>
Subject: Re: [PATCH v8] sbitmap: fix io hung due to race on
 sbitmap_word::cleared


On Tue, 16 Jul 2024 16:26:27 +0800, Yang Yang wrote:
> Configuration for sbq:
>   depth=64, wake_batch=6, shift=6, map_nr=1
> 
> 1. There are 64 requests in progress:
>   map->word = 0xFFFFFFFFFFFFFFFF
> 2. After all the 64 requests complete, and no more requests come:
>   map->word = 0xFFFFFFFFFFFFFFFF, map->cleared = 0xFFFFFFFFFFFFFFFF
> 3. Now two tasks try to allocate requests:
>   T1:                                       T2:
>   __blk_mq_get_tag                          .
>   __sbitmap_queue_get                       .
>   sbitmap_get                               .
>   sbitmap_find_bit                          .
>   sbitmap_find_bit_in_word                  .
>   __sbitmap_get_word  -> nr=-1              __blk_mq_get_tag
>   sbitmap_deferred_clear                    __sbitmap_queue_get
>   /* map->cleared=0xFFFFFFFFFFFFFFFF */     sbitmap_find_bit
>     if (!READ_ONCE(map->cleared))           sbitmap_find_bit_in_word
>       return false;                         __sbitmap_get_word -> nr=-1
>     mask = xchg(&map->cleared, 0)           sbitmap_deferred_clear
>     atomic_long_andnot()                    /* map->cleared=0 */
>                                               if (!(map->cleared))
>                                                 return false;
>                                      /*
>                                       * map->cleared is cleared by T1
>                                       * T2 fail to acquire the tag
>                                       */
> 
> [...]

Applied, thanks!

[1/1] sbitmap: fix io hung due to race on sbitmap_word::cleared
      commit: 72d04bdcf3f7d7e07d82f9757946f68802a7270a

Best regards,
-- 
Jens Axboe