linux.git/lib/stackdepot.c, branch v6.8-rc2

lib/stackdepot: add printk_deferred_enter/exit guards

2023-12-29T19:58:41+00:00

Patch series "lib/stackdepot, kasan: fixes for stack eviction series", v3.

A few fixes for the stack depot eviction series ("stackdepot: allow
evicting stack traces").

This patch (of 5):

Stack depot functions can be called from various contexts that do
allocations, including with console locks taken.  At the same time, stack
depot functions might print WARNING's or refcount-related failures.

This can cause a deadlock on console locks.

Add printk_deferred_enter/exit guards to stack depot to avoid this.

Link: https://lkml.kernel.org/r/cover.1703020707.git.andreyknvl@google.com
Link: https://lkml.kernel.org/r/82092f9040d075a161d1264377d51e0bac847e8a.1703020707.git.andreyknvl@google.com
Fixes: 108be8def46e ("lib/stackdepot: allow users to evict stack traces")
Fixes: cd11016e5f52 ("mm, kasan: stackdepot implementation. Enable stackdepot for SLAB")
Signed-off-by: Andrey Konovalov 
Reported-by: Tetsuo Handa 
Closes: https://lore.kernel.org/all/000000000000f56750060b9ad216@google.com/
Reviewed-by: Marco Elver 
Cc: Alexander Potapenko 
Cc: Dmitry Vyukov 
Cc: Evgenii Stepanov 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

lib/stackdepot: adjust DEPOT_POOLS_CAP for KMSAN

2023-12-11T00:51:48+00:00

KMSAN is frequently used in fuzzing scenarios and thus saves a lot of
stack traces.  As KMSAN does not support evicting stack traces from the
stack depot, the stack depot capacity might be reached quickly with large
stack records.

Adjust the maximum number of stack depot pools for this case.

The average size of a stack trace saved into the stack depot is ~16
frames.  Thus, adjust the maximum pools number accordingly to keep the
maximum number of stack traces that can be saved into the stack depot
similar to the one that was allowed before the stack trace eviction
changes.

Link: https://lkml.kernel.org/r/301a115cf7ce8ddb42ef6de9151c2bb76ba728fc.1700502145.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov 
Cc: Alexander Potapenko 
Cc: Dmitry Vyukov 
Cc: Evgenii Stepanov 
Cc: Marco Elver 
Cc: Oscar Salvador 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

lib/stackdepot: allow users to evict stack traces

2023-12-11T00:51:47+00:00

Add stack_depot_put, a function that decrements the reference counter on a
stack record and removes it from the stack depot once the counter reaches
0.

Internally, when removing a stack record, the function unlinks it from the
hash table bucket and returns to the freelist.

With this change, the users of stack depot can call stack_depot_put when
keeping a stack trace in the stack depot is not needed anymore.  This
allows avoiding polluting the stack depot with irrelevant stack traces and
thus have more space to store the relevant ones before the stack depot
reaches its capacity.

Link: https://lkml.kernel.org/r/1d1ad5692ee43d4fc2b3fd9d221331d30b36123f.1700502145.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov 
Cc: Alexander Potapenko 
Cc: Dmitry Vyukov 
Cc: Evgenii Stepanov 
Cc: Marco Elver 
Cc: Oscar Salvador 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

lib/stackdepot: add refcount for records

2023-12-11T00:51:46+00:00

Add a reference counter for how many times a stack records has been
  added to stack depot.

Add a new STACK_DEPOT_FLAG_GET flag to stack_depot_save_flags that
  instructs the stack depot to increment the refcount.

Do not yet decrement the refcount; this is implemented in one of the
  following patches.

Do not yet enable any users to use the flag to avoid overflowing the
  refcount.

This is preparatory patch for implementing the eviction of stack records
  from the stack depot.

Link: https://lkml.kernel.org/r/a3fc14a2359d019d2a008d4ff8b46a665371ffee.1700502145.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov 
Reviewed-by: Alexander Potapenko 
Cc: Dmitry Vyukov 
Cc: Evgenii Stepanov 
Cc: Marco Elver 
Cc: Oscar Salvador 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

lib/stackdepot, kasan: add flags to __stack_depot_save and rename

2023-12-11T00:51:46+00:00

Change the bool can_alloc argument of __stack_depot_save to a u32
  argument that accepts a set of flags.

The following patch will add another flag to stack_depot_save_flags
  besides the existing STACK_DEPOT_FLAG_CAN_ALLOC.

Also rename the function to stack_depot_save_flags, as
  __stack_depot_save is a cryptic name,

Link: https://lkml.kernel.org/r/645fa15239621eebbd3a10331e5864b718839512.1700502145.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov 
Reviewed-by: Alexander Potapenko 
Cc: Dmitry Vyukov 
Cc: Evgenii Stepanov 
Cc: Marco Elver 
Cc: Oscar Salvador 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

lib/stackdepot: use list_head for stack record links

2023-12-11T00:51:46+00:00

Switch stack_record to use list_head for links in the hash table and in
  the freelist.

This will allow removing entries from the hash table buckets.

This is preparatory patch for implementing the eviction of stack records
  from the stack depot.

Link: https://lkml.kernel.org/r/4787d9a584cd33433d9ee1846b17fa3d3e1987ad.1700502145.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov 
Cc: Alexander Potapenko 
Cc: Dmitry Vyukov 
Cc: Evgenii Stepanov 
Cc: Marco Elver 
Cc: Oscar Salvador 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

lib/stackdepot: use read/write lock

2023-12-11T00:51:45+00:00

Currently, stack depot uses the following locking scheme:

1. Lock-free accesses when looking up a stack record, which allows to
   have multiple users to look up records in parallel;
2. Spinlock for protecting the stack depot pools and the hash table
   when adding a new record.

For implementing the eviction of stack traces from stack depot, the
  lock-free approach is not going to work anymore, as we will need to be
  able to also remove records from the hash table.

Convert the spinlock into a read/write lock, and drop the atomic
  accesses, as they are no longer required.

Looking up stack traces is now protected by the read lock and adding new
  records - by the write lock.  One of the following patches will add a
  new function for evicting stack records, which will be protected by the
  write lock as well.

With this change, multiple users can still look up records in parallel.

This is preparatory patch for implementing the eviction of stack records
  from the stack depot.

Link: https://lkml.kernel.org/r/9f81ffcc4bb422ebb6326a65a770bf1918634cbb.1700502145.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov 
Reviewed-by: Alexander Potapenko 
Cc: Dmitry Vyukov 
Cc: Evgenii Stepanov 
Cc: Marco Elver 
Cc: Oscar Salvador 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

lib/stackdepot: store free stack records in a freelist

2023-12-11T00:51:45+00:00

Instead of using the global pool_offset variable to find a free slot when
storing a new stack record, mainlain a freelist of free slots within the
allocated stack pools.

A global next_stack variable is used as the head of the freelist, and the
next field in the stack_record struct is reused as freelist link (when the
record is not in the freelist, this field is used as a link in the hash
table).

This is preparatory patch for implementing the eviction of stack records
from the stack depot.

Link: https://lkml.kernel.org/r/b9e4c79955c2121b69301778643b203d3fb09ccc.1700502145.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov 
Reviewed-by: Alexander Potapenko 
Cc: Dmitry Vyukov 
Cc: Evgenii Stepanov 
Cc: Marco Elver 
Cc: Oscar Salvador 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

lib/stackdepot: store next pool pointer in new_pool

2023-12-11T00:51:45+00:00

Instead of using the last pointer in stack_pools for storing the pointer
to a new pool (which does not yet store any stack records), use a new
new_pool variable.

This a purely code readability change: it seems more logical to store the
pointer to a pool with a special meaning in a dedicated variable.

Link: https://lkml.kernel.org/r/448bc18296c16bef95cb3167697be6583dcc8ce3.1700502145.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov 
Reviewed-by: Alexander Potapenko 
Cc: Dmitry Vyukov 
Cc: Evgenii Stepanov 
Cc: Marco Elver 
Cc: Oscar Salvador 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

lib/stackdepot: rename next_pool_required to new_pool_required

2023-12-11T00:51:45+00:00

Rename next_pool_required to new_pool_required.

This a purely code readability change: the following patch will change
stack depot to store the pointer to the new pool in a separate variable,
and "new" seems like a more logical name.

Link: https://lkml.kernel.org/r/fd7cd6c6eb250c13ec5d2009d75bb4ddd1470db9.1700502145.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov 
Reviewed-by: Alexander Potapenko 
Cc: Dmitry Vyukov 
Cc: Evgenii Stepanov 
Cc: Marco Elver 
Cc: Oscar Salvador 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton