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Re: svn commit: r1591919 - in /subversion/trunk/subversion: include/ include/private/ libsvn_fs/ libsvn_fs_base/bdb/ libsvn_fs_fs/ libsvn_fs_x/ libsvn_ra_svn/ libsvn_subr/ svnserve/ tests/ tests/libsvn_fs_fs/

From: Ivan Zhakov <ivan_at_visualsvn.com>
Date: Mon, 5 May 2014 16:57:41 +0400

On 5 May 2014 16:47, Bert Huijben <bert_at_qqmail.nl> wrote:
>
>
>> -----Original Message-----
>> From: stefan2_at_apache.org [mailto:stefan2_at_apache.org]
>> Sent: vrijdag 2 mei 2014 16:08
>> To: commits_at_subversion.apache.org
>> Subject: svn commit: r1591919 - in /subversion/trunk/subversion: include/
>> include/private/ libsvn_fs/ libsvn_fs_base/bdb/ libsvn_fs_fs/ libsvn_fs_x/
>> libsvn_ra_svn/ libsvn_subr/ svnserve/ tests/ tests/libsvn_fs_fs/
>>
>> Author: stefan2
>> Date: Fri May 2 14:07:40 2014
>> New Revision: 1591919
>>
>> URL: http://svn.apache.org/r1591919
>> Log:
>> APR mutexes don't support recursive locking on all platforms.
>> As a result, trying to take out the same lock twice in the
>> same thread will cause a lock up under e.g. Linux. This patch
>> adds an option to svn_mutex__t that detects recursive locking
>> attempts in most cases and returns a proper error.
>>
>> The idea is simply to store the thread ID of the lock OWNER
>> along the actual mutex object. If that matches the current
>> thread's ID, there is a violation. As the current thread
>> cannot race with itself and because any other thread uses a
>> different thread ID, setting and comparing this aux. info can
>> be done safely.
>>
>> Also, we may allow for false negatives here since we only try
>> to detect code sequences that are already illegal in the first
>> place. We also don't make that check mandatory as access to
>> thread IDs and their comparison may be somewhat expensive on
>> some systems - which would impair the futex-like behavior that
>> we assume in some places like the caches.
>>
>> A more detailed description has been added to the source code.
>> A FSFS-based test is added as that has been the origin of the
>> feature request.
>>
>> Current users will be updated as follows. FS level locks and
>> library / module initialization will enable recursion detection.
>> Potentially runtime critical, internal use disables it.
>>
>> * subversion/include/svn_error_codes.h
>> (SVN_ERR_RECURSIVE_LOCK): Define a new error code for invalid
>> locking schemes.
>>
>> * subversion/include/private/svn_mutex.h
>> (svn_mutex__t): Our mutex is now a struct as we add aux.
>> data to it.
>> (svn_mutex__init): Add the CHECKED option.
>>
>> * subversion/libsvn_subr/mutex.c
>> (svn_mutex__t): Define the mutex structure and and document
>> the aux. data extensively.
>> (svn_mutex__init): Update constructor.
>> (svn_mutex__lock): Optionally, check for recursive locking attempts
>> and update the associtated aux. data.
>> (svn_mutex__unlock): Optionally, update the aux. data for recursive
>> lock detection.
>>
>> * subversion/tests/libsvn_fs_fs/fs-fs-pack-test.c
>> (never_reached,
>> lock_again): Callback functions required by the new test.
>> (recursive_locking): New test expecting an SVN_ERR_RECURSIVE_LOCK.
>> (test_funcs): Register the new test.
>
> This new test currently causes a deadlock on Windows and a test failure on OpenBSD.
>
[...]

> Windows:
> Hang in
> [[[
>> libapr-1.dll!apr_file_lock(apr_file_t * thefile, int type) Line 35 C
> fs-fs-pack-test.exe!svn_io_lock_open_file(apr_file_t * lockfile_handle, int exclusive, int nonblocking, apr_pool_t * pool) Line 2137 C
> fs-fs-pack-test.exe!svn_io_file_lock2(const char * lock_file, int exclusive, int nonblocking, apr_pool_t * pool) Line 2239 C
> fs-fs-pack-test.exe!get_lock_on_filesystem(const char * lock_filename, apr_pool_t * pool) Line 115 C
> fs-fs-pack-test.exe!with_some_lock_file(with_lock_baton_t * baton) Line 202 C
> fs-fs-pack-test.exe!with_lock(void * baton, apr_pool_t * pool) Line 248 C
> fs-fs-pack-test.exe!svn_fs_fs__with_all_locks(svn_fs_t * fs, svn_error_t * (void *, apr_pool_t *) * body, void * baton, apr_pool_t * pool) Line 424 C
> fs-fs-pack-test.exe!lock_again(void * baton, apr_pool_t * pool) Line 1148 C
> fs-fs-pack-test.exe!with_some_lock_file(with_lock_baton_t * baton) Line 230 C
> fs-fs-pack-test.exe!with_lock(void * baton, apr_pool_t * pool) Line 248 C
> fs-fs-pack-test.exe!with_some_lock_file(with_lock_baton_t * baton) Line 230 C
> fs-fs-pack-test.exe!with_lock(void * baton, apr_pool_t * pool) Line 248 C
> fs-fs-pack-test.exe!with_some_lock_file(with_lock_baton_t * baton) Line 230 C
> fs-fs-pack-test.exe!with_lock(void * baton, apr_pool_t * pool) Line 248 C
> fs-fs-pack-test.exe!svn_fs_fs__with_all_locks(svn_fs_t * fs, svn_error_t * (void *, apr_pool_t *) * body, void * baton, apr_pool_t * pool) Line 424 C
> fs-fs-pack-test.exe!recursive_locking(const svn_test_opts_t * opts, apr_pool_t * pool) Line 1159 C
> fs-fs-pack-test.exe!test_thread(apr_thread_t * thread, void * data) Line 519 C
> libapr-1.dll!dummy_worker(void * opaque) Line 79 C
> ]]]
>
Most likely this happens because file locks are *per file handle* on
Windows: not per-process as on posix. That means that one thread
cannot obtain lock to file using different file handles.

-- 
Ivan Zhakov
CTO | VisualSVN | http://www.visualsvn.com
Received on 2014-05-05 14:59:30 CEST

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