From: Thomas Lamprecht <t.lamprecht@proxmox.com>
To: Proxmox VE development discussion <pve-devel@lists.proxmox.com>,
Fiona Ebner <f.ebner@proxmox.com>
Subject: Re: [pve-devel] [PATCH qemu] add fix for crash during live migration in combination with block flush
Date: Wed, 15 Jan 2025 17:28:17 +0100 [thread overview]
Message-ID: <3e462976-81be-4025-b7b0-b546a51c2246@proxmox.com> (raw)
In-Reply-To: <20250108130304.343460-1-f.ebner@proxmox.com>
Am 08.01.25 um 14:03 schrieb Fiona Ebner:
> Setting blk->root is a graph change operation and thus needs to be
> protected by the block graph write lock in blk_remove_bs(). The
> assignment to blk->root in blk_insert_bs() is already protected by
> the block graph write lock.
>
> In particular, the graph read lock in blk_co_do_flush() could
> previously not ensure that blk_bs(blk) would always return the same
> value during the locked section, which could lead to a segfault [0] in
> combination with migration [1].
>
> From the user-provided backtraces in the forum thread [1], it seems
> like blk_co_do_flush() managed to get past the
> blk_co_is_available(blk) check, meaning that blk_bs(blk) returned a
> non-NULL value during the check, but then, when calling
> bdrv_co_flush(), blk_bs(blk) returned NULL.
>
> [0]:
>
>> 0 bdrv_primary_child (bs=bs@entry=0x0) at ../block.c:8287
>> 1 bdrv_co_flush (bs=0x0) at ../block/io.c:2948
>> 2 bdrv_co_flush_entry (opaque=0x7a610affae90) at block/block-gen.c:901
>
> [1]: https://forum.proxmox.com/threads/158072
>
> Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
> ---
>
> Upstream submission of the same patch:
> https://lore.kernel.org/qemu-devel/20250108124649.333668-1-f.ebner@proxmox.com/T/
I only skimmed the upstream discussion, but seems that there is still some
issue left; so should I wait this version out?
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next prev parent reply other threads:[~2025-01-15 16:28 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-01-08 13:03 Fiona Ebner
2025-01-15 16:28 ` Thomas Lamprecht [this message]
2025-01-16 10:30 ` Fiona Ebner
2025-01-16 13:10 ` Thomas Lamprecht
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