Deadlock while accessing mtdchar device while erase in progress
Laurent Pinchart
laurentp at cse-semaphore.com
Fri Dec 28 05:04:26 EST 2007
Hi everybody,
I sent a mail two weeks ago about an MTD-related deadlock. I haven't received
any answer so far, so I'm pinging the list just in case the message was
missed. Here's the original mail.
I'm having troubles fixing an MTD-related deadlock. I'm not sure if the
problem comes from an MTD and/or JFFS2 kernel bug, or from some userspace
operation performed as root that I shouldn't have started in the first place.
I'd appreciate if someone could share his thoughts (and experience :-)) about
this.
Some background.
My embedded system has a single NOR flash chip (cfi_cmdset_0002 driver) with
128kB sectors. Flash space is divided in 4 partitions, the last one used with
a JFFS2 filesystem.
A userspace process run as root sets its scheduling policy to SCHED_RR. It
writes 400kB of data to the JFFS2 filesystem and restarts by exec()ing
itself, inheriting the SCHED_RR policy.
Soon after being restarted, it opens /dev/mtd0 (boot loader partition) and
reads a few bytes of data. It then close() /dev/mtd0, at which point the
kernel deadlocks.
I added debugging messages to the MTD subsystem and it turned out my process
blocks in cfi_amdstd_sync (drivers/mtd/chips/cfi_cmdset_0002.c). chip->state
is set to FL_ERASING, and the kernel keeps scheduling in the default case.
I'm not sure what goes wrong. I expect the JFFS2 garbage collector to have
kicked in. It might be erasing sectors when I close() /dev/mtd0, at which
point the mtdchar driver tries to sync() the flash and locks in
cfi_amdstd_sync because my process, being scheduled with a SCHED_RR policy,
never gives the JFFS2 garbage collector a chance to run. That's just a wild
guess though.
Any help regarding how to better diagnose the problem (to confirm or reject
the above suspicion) will be appreciated. A fix would be even more
welcome :-)
Best regards,
--
Laurent Pinchart
CSE Semaphore Belgium
Chaussée de Bruxelles, 732A
B-1410 Waterloo
Belgium
T +32 (2) 387 42 59
F +32 (2) 387 42 75
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