add environment variable to avoid RTLD_DEEPBIND when loading modules
#6063
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grondo
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Jun 28, 2024
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This LGTM. I just wonder about the need for flux_deepbind() in the public API.
Also, I wonder if the result of getenv () could be cached so we don't check multiple times for an environment variable that will almost never be present (or that could just be premature optimization)
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grondo
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Jul 1, 2024
garlick
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Jul 1, 2024
src/common/libflux/plugin.c
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| @@ -34,6 +36,21 @@ | |||
| #define UUID_STR_LEN 37 // defined in later libuuid headers | |||
| #endif | |||
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| static int use_deepbind = 1; | |||
| static pthread_once_t deepbind_once = PTHREAD_ONCE_INIT; | |||
| static void init_use_deepbind () { | |||
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Style: void parameter, open brace on new line
src/common/libflux/plugin.c
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| } | ||
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| int plugin_deepbind () { | ||
| pthread_once(&deepbind_once, init_use_deepbind); |
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Style: open brace for function on new line, space before open paren in pthread_once
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I think that's all addressed. |
garlick
reviewed
Jul 1, 2024
src/common/libflux/plugin_private.h
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| #ifndef FLUX_CORE_PLUGIN_PRIVATE_H | ||
| #define FLUX_CORE_PLUGIN_PRIVATE_H | ||
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| int plugin_deepbind (); |
grondo
changed the title
RTLD_DEEPBIND when loading modules
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Restarted the inception builder which had failed. I could not discern why. |
problem: I recently needed to get a heap trace of flux to track down why fluxion was using so much memory, that's another sordid tale I'm afraid, but every tool I tried reported freeing unallocated pointers. There is a bad interaction between recent versions of glibc, that removed the allocator hooks, and the RTLD_DEEPBIND flag. Essentially it's nearly impossible to consistely replace the allocator interface in all the libraries consistently, whether using LD_PRELOAD or anything else. Thankfully just turning that off works, as long as we don't have symbol conflicts. solution: Replace use of FLUX_DEEPBIND with calls to `flux_deepbind ()` which checks for an environment variable, `FLUX_LOAD_WITH_DEEPBIND`, and if that variable is both set and contains 0 returns 0, otherwise it returns FLUX_DEEPBIND. This allows for easy flipping to load flux using say jemalloc, tcmalloc or the interposer library for heaptrack without a rebuild.
problem: spellcheck failed on the explanation of the deepbind environment variable solution: add appropriate tokens to dictionary
Codecov ReportAttention: Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## master #6063 +/- ##
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- Coverage 83.34% 83.31% -0.03%
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Files 521 521
Lines 84389 84396 +7
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- Hits 70330 70317 -13
- Misses 14059 14079 +20
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Add an environment variable to control whether we actually apply the RTLD_DEEPBIND flag when calling dlopen. More details in the commit message, but this makes it possible to run flux with an alternate allocator using LD_PRELOAD or certain other things that make heap tracing and certain other debugging and tracing tasks much easier.