Re: [ECOS] Nested mutex problem (fdlock in fd.cxx)

[Gary Thomas <gary at chez-thomas dot org>]

On Wed, 2002-06-19 at 09:29, Jurica Baricevic wrote:
> Hi.
> 
> I have found a small problem with mutex 'fdlock' in
> 'io/fileio/current/src/fd.cxx' for one particular case. It seems that it is
> possible to create nested mutex lock case in a file system implementation.
> Specifically, call to close() function locks 'fdlock', which then may lead
> to another lock by calling 'printf' in lower layers (within the particular
> file system implementation). This is because 'printf' may get to
> cyg_fp_get() function, which is also locking 'fdlock'. Unfortunately, eCos
> does not support nested mutexes.
> 
> It may sound odd that 'printf' is used within file system functions.
> Nevertheless, it may be quite useful for reporting errors in low level
> functions (egg. bad block warning, write protect notification, etc.). It is
> worth to mention that I am debugging some proprietary file system under
> eCos.
> 

Because of situations like this, we recommend using 'diag_printf()'
for debug/error messages.

> 
> Please, take a look at the following stack backtrace (simplified for easier
> reading):
> 
> #0  cyg_assert_fail
> #1  Cyg_Mutex::lock at mutex.cxx:237
> #2  cyg_fp_get at fd.cxx:258    <- trying to lock fdlock for 2nd time
> #3  readwrite at io.cxx:87
> #4  write at io.cxx:148
> #5  Cyg_StdioStream::flush_output_unlocked at io.inl:131
> #6  Cyg_StdioStream::write at stream.cxx:673
> #7  vfnprintf at vfnprintf.cxx:265
> #8  printf at printf.cxx:66
> #9  (myfilesystem_write_sector)
> #10 (myfilesystem_flush_buffer)
> #11 (myfilesystem_fo_close)
> #12 fp_ucount_dec at fd.cxx:149
> #13 fd_close at fd.cxx:174
> #14 cyg_fd_free at fd.cxx:238   <- fdlock locked (1st time) prior to call to
> fd_close.
> #15 close at io.cxx:172
> (...)
> 
> 
> Due to the lack of time, I still did not switch to latest eCos 2.0 on CVS.
> Instead, I am using eCos CVS tree from February (I think). Therefore, I
> would apologize for asking this in the case that the issue has been already
> solved. Anyway, I checked the eCos 2.0 and didn't notice anything new
> related to my problem.
> 
> I would appreciate any advice on how to avoid this problem.
> 
> Thanks and best regards,
> Jura
> 
> 
> 
> -- 
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> and search the list archive: http://sources.redhat.com/ml/ecos-discuss



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