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<p style="color: #777777;">
<a href="https://gitlab.rtems.org/sebhub">Sebastian Huber</a>
<a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/issues/5311#note_134878">commented</a>:
</p>
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<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">There are more issues associated with the reference counting change.</p>
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<p style="color: #3a383f; margin: 0 0 1rem;">There is an API change on a release branch (<code style='font-size: 90%; color: #18171d; word-wrap: break-word; border-radius: .25rem; background-color: #ececef; margin-top: 0; font-weight: inherit; white-space: break-spaces; overflow-wrap: break-word; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;'>rtems_libio_fcntl_flags()</code> was renamed).</p>
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<p style="color: #3a383f; margin: 0 0 1rem;">There are ABI changes (<code style='font-size: 90%; color: #18171d; word-wrap: break-word; border-radius: .25rem; background-color: #ececef; margin-top: 0; font-weight: inherit; white-space: break-spaces; overflow-wrap: break-word; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;'>LIBIO_FLAGS_FREE</code> and related flags).</p>
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<p style="color: #3a383f; margin: 0 0 1rem;">With reference counting you must never set the count to a specific value. The only valid operations are increments and decrements. This leads to problems:</p>
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<pre class="code highlight js-syntax-highlight language-plaintext" v-pre="true" style='display: block; font-size: 14px; color: #3a383f; line-height: 1.6em; overflow-x: auto; border-radius: .25rem; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: #fbfafd; margin: 0 0 1rem; padding: 12px; border: 1px solid #dcdcde;'><code style='font-size: inherit; color: inherit; word-wrap: normal; word-break: keep-all; border-radius: .25rem; background-color: inherit; white-space: pre; margin-top: 0; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; overflow-wrap: normal; padding: unset;'><span id="LC1" class="line" lang="plaintext" style="margin-top: 0;">void rtems_libio_free_iop(</span>
<span id="LC2" class="line" lang="plaintext"> rtems_libio_t *iop</span>
<span id="LC3" class="line" lang="plaintext">)</span>
<span id="LC4" class="line" lang="plaintext">{</span>
<span id="LC5" class="line" lang="plaintext"> size_t zero;</span>
<span id="LC6" class="line" lang="plaintext"></span>
<span id="LC7" class="line" lang="plaintext"> rtems_libio_lock();</span>
<span id="LC8" class="line" lang="plaintext"></span>
<span id="LC9" class="line" lang="plaintext"> if ( !rtems_libio_iop_is_free( iop ) ) {</span>
<span id="LC10" class="line" lang="plaintext"><- Lets assume someone calls rtems_libio_iop_hold() here and gets a reference count of 1.</span>
<span id="LC11" class="line" lang="plaintext"> /*</span>
<span id="LC12" class="line" lang="plaintext"> * Clear the flags. All references should have been dropped.</span>
<span id="LC13" class="line" lang="plaintext"> */</span>
<span id="LC14" class="line" lang="plaintext"> _Atomic_Store_uint( &iop->flags, LIBIO_FLAGS_FREE, ATOMIC_ORDER_RELAXED );</span>
<span id="LC15" class="line" lang="plaintext"><- This sets the reference count to zero. Lets assume the caller of rtems_libio_iop_hold() notices that the file descriptor is bad. It calls rtems_libio_iop_drop(). The reference count is now -1.</span>
<span id="LC16" class="line" lang="plaintext"></span>
<span id="LC17" class="line" lang="plaintext"> rtems_filesystem_location_free( &iop->pathinfo );</span></code></pre>
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<p style="color: #3a383f; margin: 0 0 1rem;">Calling <code style='font-size: 90%; color: #18171d; word-wrap: break-word; border-radius: .25rem; background-color: #ececef; margin-top: 0; font-weight: inherit; white-space: break-spaces; overflow-wrap: break-word; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;'>rtems_filesystem_location_free( &iop->pathinfo )</code> while owning the libio lock (<code style='font-size: 90%; color: #18171d; word-wrap: break-word; border-radius: .25rem; background-color: #ececef; font-weight: inherit; white-space: break-spaces; overflow-wrap: break-word; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;'>rtems_libio_lock()</code>) may cause lock order reversal issues (deadlock).</p>
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<p style="color: #3a383f; margin: 0 0 1rem;">You should not use snapshots of the flags, actions should be based on state changes. For example:</p>
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<pre class="code highlight js-syntax-highlight language-plaintext" v-pre="true" style='display: block; font-size: 14px; color: #3a383f; line-height: 1.6em; overflow-x: auto; border-radius: .25rem; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: #fbfafd; margin: 0 0 1rem; padding: 12px; border: 1px solid #dcdcde;'><code style='font-size: inherit; color: inherit; word-wrap: normal; word-break: keep-all; border-radius: .25rem; background-color: inherit; white-space: pre; margin-top: 0; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; overflow-wrap: normal; padding: unset;'><span id="LC1" class="line" lang="plaintext" style="margin-top: 0;">@@ -226,7 +226,10 @@ static int vfcntl(</span>
<span id="LC2" class="line" lang="plaintext"> </span>
<span id="LC3" class="line" lang="plaintext"> if (ret >= 0) {</span>
<span id="LC4" class="line" lang="plaintext"> int err = (*iop->pathinfo.handlers->fcntl_h)( iop, cmd );</span>
<span id="LC5" class="line" lang="plaintext">- if (err) {</span>
<span id="LC6" class="line" lang="plaintext"></span>
<span id="LC7" class="line" lang="plaintext"><-- Here you started with a valid open file descriptor. The higher level code cannot decide the outcome of the fcntl_h handler.</span>
<span id="LC8" class="line" lang="plaintext"></span>
<span id="LC9" class="line" lang="plaintext">+ if (err == 0 && !rtems_libio_iop_is_open( iop ) ) {</span>
<span id="LC10" class="line" lang="plaintext">+ err = EBADF;</span>
<span id="LC11" class="line" lang="plaintext">+ }</span>
<span id="LC12" class="line" lang="plaintext">+ if (err != 0) {</span>
<span id="LC13" class="line" lang="plaintext"> errno = err;</span>
<span id="LC14" class="line" lang="plaintext"> ret = -1;</span>
<span id="LC15" class="line" lang="plaintext"> }</span></code></pre>
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<p style="color: #3a383f; margin: 0 0 1rem;">I think there is an issue with the recent fixes.</p>
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<p style="color: #3a383f; margin: 0 0 1rem;">My patch doesn't work also.</p>
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