---
- branch: netbsd-10
  date: Sat Feb  3 12:39:17 UTC 2024
  files:
  - new: 1.42.4.1
    old: '1.42'
    path: src/sys/dev/sdmmc/ld_sdmmc.c
    pathrev: src/sys/dev/sdmmc/ld_sdmmc.c@1.42.4.1
    type: modified
  id: 20240203T123917Z.bfa91ba4c27348991b0f636a61739ba4f596f7a9
  log: "Pull up following revision(s) (requested by riastradh in ticket #566):\n\n\tsys/dev/sdmmc/ld_sdmmc.c:
    revision 1.43\n\nld@sdmmc(4): Hack around deadlock in cache sync on detach.\n\nYanking
    a card triggers the sdmmc discovery task, which runs in the\nsdmmc task thread,
    to detach any attached child devices.\n\nDetaching ld@sdmmc triggers a cache flush
    (via ldbegindetach ->\ndisk_begindetach -> ld_lastclose -> ld_flush -> ioctl DIOCCACHESYNC),\nwhich
    is implemented by scheduling a task to do sdmmc_mem_flush_cache\nand then waiting
    for it to complete.\n\nThe sdmmc_mem_cache_flush is done by an sdmmc task so it
    happens\nafter all previously scheduled I/O operations -- that way the cache\nflush
    doesn't complete until the previously scheduled I/O operations\nare complete.\n\nHowever,
    when the cache flush task is issued from the discovery task,\nthis doesn't work,
    because the cache flush task can't start until the\ndiscovery task has returned
    -- but the discovery task won't return\nuntil the cache flush task has completed.\n\nTo
    work around this deadlock, which usually happens only when the\ndevice has been
    yanked anyway so further I/O would be lost anyway,\njust do the cache flush synchronously
    in DIOCCACHESYNC if we're\nrunning in the task thread.\n\nThis isn't quite right
    -- implementation details of the task thread\nshouldn't bleed into ld@sdmmc, and
    running the cache sync _before_\nany subsequently scheduled I/O tasks is asking
    for trouble -- but it\nshould serve to avoid the deadlock in PR kern/57870 until
    we can fix\na host of concurrency bugs in sdmmc by fixing the locking scheme and\nrunning
    discovery in a separate thread from tasks.\n"
  module: src
  subject: 'CVS commit: [netbsd-10] src/sys/dev/sdmmc'
  unixtime: '1706963957'
  user: martin