On Wed, Aug 15 2018, Jeff Layton wrote:
> On Wed, 2018-08-15 at 14:28 +0200, Krzysztof Kozlowski wrote:
>> Hi,
>>
>> Bisect pointed commit ce3147990450a68b3f549088b30f087742a08b5d
>> ("fs/locks: allow a lock request to block other requests.") to failure
>> boot of NFSv4 with root on several boards.
>>
>> Log is here:
>> https://krzk.eu/#/builders/21/builds/836/steps/12/logs/serial0
>>
>> With several errors:
>> kernel BUG at ../fs/locks.c:336!
>> Unable to handle kernel NULL pointer dereference at virtual address 00000004
>>
>> Configuration:
>> 1. exynos_defconfig
>> 2. Arch ARM Linux
>> 3. Boards:
>> a. Odroid family (ARMv7, octa-core (Cortex-A7+A15), Exynos5422 SoC)
>> b. Toradex Colibri VF50 (ARMv7, UP, Cortex-A5)
>> 4. Systemd: v236, 238
>> 5. All boards boot from TFTP with NFS root (NFSv4)
>>
>> On Colibri VF50 I got slightly different errors:
>> [ 11.663204] Internal error: Oops - undefined instruction: 0 [#1] ARM
>> [ 12.455273] Unable to handle kernel NULL pointer dereference at
>> virtual address 00000004
>> and only with some specific GCC (v6.3) or with other conditions which
>> I did not bisect yet. Maybe Colibri's failure is unrelated to that
>> commit.
>>
>> Best regards,
>> KrzysztofThanks a lot for the report Krzysztof!! > > The BUG is due to a lock being freed when the fl_blocked list wasn't > empty (implying that there were still blocked locks waiting on it). > > There are a number of calls to locks_delete_lock_ctx in posix_lock_inode > and I don't think the fl_blocked list is being handled properly with all > of them. It only transplants the blocked locks to a new lock when there > are surviving locks on the list, and that may not be the case when the > whole file is being unlocked. locks_delete_lock_ctx() calls locks_unlink_lock_ctx() which calls locks_wake_up_block() which doesn't only wake_up the blocks, but also detached them. When that function completes, ->fl_blocked must be empty. The trace shows the locks_free_lock() call at the end of fcntl_setlk64() as the problematic call. This suggests that do_lock_file_wait() exited with ->fl_blocked non-empty, which it shouldn't. I think we need to insert a call to locks_wake_up_block() in do_lock_file_wait() before it returns. I cannot find a sequence that would make this necessary, but it isn't surprising that there might be one. I'll dig through the code a bit more later and make sure I understand what is happening. Thanks, NeilBrown
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