Re: [PATCH v3 1/1] md/raid1: serialize overlap io for writemostly disk

["Yu Kuai" <yukuai@fnnas.com>]

在 2026/3/24 15:24, Xiao Ni 写道:

> Previously, using wait_event() would wake up all waiters simultaneously,
> and they would compete for the tree lock. The bio which gets the lock
> first will be handled, so the write sequence cannot be guaranteed.
>
> For example:
> bio1(100,200)
> bio2(150,200)
> bio3(150,300)
>
> The write sequence of fast device is bio1,bio2,bio3. But the write sequence
> of slow device could be bio1,bio3,bio2 due to lock competition. This causes
> data corruption.
>
> Replace waitqueue with a fifo list to guarantee the write sequence. And it
> also needs to iterate the list when removing one entry. If not, it may miss
> the opportunity to wake up the waiting io.
>
> For example:
> bio1(1,3), bio2(2,4)
> bio3(5,7), bio4(6,8)
> These four bios are in the same bucket. bio1 and bio3 are inserted into
> the rbtree. bio2 and bio4 are added to the waiting list and bio2 is the
> first one. bio3 returns from slow disk and tries to wake up the waiting
> bios. bio2 is removed from the list and will be handled. But bio1 hasn't
> finished. So bio2 will be added into waiting list again. Then bio1 returns
> from slow disk and wakes up waiting bios. bio4 is removed from the list
> and will be handled. Now bio1, bio3 and bio4 all finish and bio2 is left
> on the waiting list. So it needs to iterate the waiting list to wake up
> the right bio.
>
> Signed-off-by: Xiao Ni<xni@redhat.com>
> ---
> v2: use prepare_to_wait_exclusive
> v3: return back to self managed fifo list to find the right waiting node
>   drivers/md/md.c    |  1 -
>   drivers/md/md.h    |  5 ++++-
>   drivers/md/raid1.c | 45 ++++++++++++++++++++++++++++++++++-----------
>   3 files changed, 38 insertions(+), 13 deletions(-)
Applied to md-7.1

-- 
Thansk,
Kuai