From: NeilBrown <firstname.lastname@example.org>
To: Jeff Layton <email@example.com>, Krzysztof Kozlowski <firstname.lastname@example.org>
Cc: Alexander Viro <email@example.com>,
"J. Bruce Fields" <firstname.lastname@example.org>,
Subject: Re: [BUG][BISECT] NFSv4 root failures after "fs/locks: allow a lock request to block other requests."
Date: Thu, 16 Aug 2018 15:19:59 +1000 [thread overview]
Message-ID: <email@example.com> (raw)
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On Wed, Aug 15 2018, Jeff Layton wrote:
> On Wed, 2018-08-15 at 14:28 +0200, Krzysztof Kozlowski wrote:
>> 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:
>> With several errors:
>> kernel BUG at ../fs/locks.c:336!
>> Unable to handle kernel NULL pointer dereference at virtual address 00000004
>> 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
>> Best regards,
Thanks 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.
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next prev parent reply other threads:[~2018-08-16 8:15 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-15 12:28 [BUG][BISECT] NFSv4 root failures after "fs/locks: allow a lock request to block other requests." Krzysztof Kozlowski
2018-08-15 12:44 ` Jeff Layton
2018-08-15 14:19 ` Jeff Layton
2018-08-16 5:19 ` NeilBrown [this message]
2018-08-21 5:11 ` NeilBrown
2018-08-21 11:14 ` Jeff Layton
2018-08-21 21:15 ` NeilBrown
2018-08-23 23:17 ` NeilBrown
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