JFFS2 deadlock, kernel 3.4.11

[Joakim Tjernlund]

linux-mtd-bounces at lists.infradead.org wrote on 2012/10/02 16:19:10:
>
> Hello all,
>
> I have encountered multiple times a deadlock between two JFFS2 threads:

[SNIP]

>
> The target system is an SoC with a dual ARMv7 (Cortex-A9), and we are
> running the long-term 3.4.11 kernel (whose fs/jffs2/ seems to be pretty
> close to the latest mainline kernel). The deadlock occurred when using scp
> to copy files from a host system to the target system.
>
> The GC thread hangs in lock_page(page), the write thread hangs in the
> first mutex_lock(&f->sem). The cause seems to be an AB-BA deadlock:
>
> jffs2_garbage_collect_live
>     mutex_lock(&f->sem)                         (A)
>     jffs2_garbage_collect_dnode [inlined]
>         jffs2_gc_fetch_page
>             read_cache_page_async
>                 do_read_cache_page
>                     lock_page(page) [inlined]
>                         __lock_page             (B) ***
>
> jffs2_write_begin
>     grab_cache_page_write_begin
>         find_lock_page
>             lock_page(page)                     (B)
>     mutex_lock(&f->sem)                         (A) ***
>
> I have manually analyzed the stacks and confirmed that both threads sit on
> the theme 'struct page'.
>

hmm, not something I have seen but your analysis seems spot on. With any luck
you only need to move the mutex_lock in the write begin before lock_page. I
am only guessing now though.

 Jocke